Lennox International Inc Furnace Dave Signature Collection Gas Upflow Horizontal Air Dis 506763a

Lennox International Inc. Furnace SL280UH070V36A Lennox_SL280UHV_IOM

DAVE LENNOX SIGNATURE COLLECTION GAS FURNACE UPFLOW HORIZONTAL AIR DISCHARGE to the manual 33807615-f9a6-4b72-ba73-52431e7cefef

2015-02-09

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INSTALLATION
INSTRUCTIONS
SL280UHV

2011 Lennox Industries Inc.
Dallas, Texas, USA

DAVE LENNOX SIGNATURE®
COLLECTION GAS FURNACE
UPFLOW / HORIZONTAL AIR DISCHARGE

506763−01
06/2011
Supersedes 03/2011

Litho U.S.A.

THIS MANUAL MUST BE LEFT WITH THE
HOMEOWNER FOR FUTURE REFERENCE
This a safety alert symbol and should never be ignored.
When you see this symbol on labels or in manuals, be alert
to the potential for personal injury or death.

CAUTION

UPFLOW

As with any mechanical equipment, personal injury
can result from contact with sharp sheet metal
edges. Be careful when you handle this equipment.

AIR FLOW

NOTICE
A thermostat is not included and must be ordered
separately.
AIR FLOW

HORIZONTAL LEFT

The Lennox icomfort Touch® thermostat must be
used in communicating applications.

AIR FLOW

HORIZONTAL RIGHT

In non−communicating applications, the Lennox
ComfortSense® 7000 thermostat may be used, as
well as other non−communicating thermostats.

WARNING

In all cases, setup is critical to ensure proper system operation.

Improper installation, adjustment, alteration, service
or maintenance can cause property damage, personal injury or loss of life. Installation and service must
be performed by a licensed professional installer (or
equivalent), service agency or the gas supplier.

Field wiring for both communicating and non−communicating applications is illustrated in diagrams,
which begin on Page 27.

Table of Contents
Unit Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Parts Arrangement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SL280UHV Gas Furnace . . . . . . . . . . . . . . . . . . . . . . . . .
Shipping and Packing List . . . . . . . . . . . . . . . . . . . . . . . .
Safety Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Use of Furnace as a Construction Heater . . . . . . . . . . .
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Combustion, Dilution & Ventilation Air . . . . . . . . . . . . . .
Setting Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Duct System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Gas Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2
3
4
4
4
5
5
6
9
12
12
13
23

Electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Integrated Control Settings . . . . . . . . . . . . . . . . . . . . . . .
Blower Performance Data . . . . . . . . . . . . . . . . . . . . . . . .
Unit Start−Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Gas Pressure Adjustment . . . . . . . . . . . . . . . . . . . . . . . .
Proper Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
High Altitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Other Unit Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . .
Heating Sequence of Operation . . . . . . . . . . . . . . . . . . .
Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Planned Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Repair Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Integrated Control Diagnostic Codes . . . . . . . . . . . . . . .
Program Unit Capacity/Size Mode . . . . . . . . . . . . . . . . .
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

06/11

*2P0611*

506763−01

Page 1

25
36
39
51
52
52
53
54
54
56
59
59
60
67
68

*P506763-01*

Unit Dimensions − inches (mm)
1NOTE

− 60C and 60D units that require air volumes over 1800 cfm
(850 L/s) must have one of the following:
1. Return air from single side transition will accommodate 20 x 25 x1 in.
(508 x 635 x 25) cleanable air filter. (Required to maintain proper air
D
velocity)
2. Single side return air with optional RAB Return
Air Base.
3. Return air from bottom and one side.
FLUE OUTLET
4. Return air from both sides.
(Top)
5. Return air from bottom.
See blower performance tables for additional information
2Flue outlet may be horizontal but furnace must be
vented vertically
3Optional external side return air filter kit cannot be used
3 OPTIONAL
with the optional RAB Return Air Base.

3−1/8 (79)

SUPPLY AIR
OPENING

23−3/4
(603)

EXTERNAL
SIDE RETURN
AIR FILTER KIT
(Either Side)

A
B

25
(635)

TOP VIEW
27−3/4
(705)

1−1/2 (38)
Front Panel

9/16 (14)

3−1/4 (83)

2 FLUE

OUTLET
(Either Side)

3 OPTIONAL

EXTERNAL
SIDE RETURN
AIR FILTER KIT
(Either Side)

9−1/8 (232) Right
8−5/8 (219) Left

GAS PIPING INLET
(Either Side)

33
(838)
5−3/8 (137) Right
2−3/4 (70) Left

ELECTRICAL INLET
(Either Side)

14−3/4
(375)

AIR FLOW

3/4
(19)

C
1 Bottom

Return
Air Opening

Side Return
Air Opening
(Either Side)

5/8
(16)

14
(356)

1−15/16 (49)
3−1/4
(83)

FRONT VIEW

Model No.

1−1/2
(38)

23
(584)

16
(406)

3/4
(19)

9/16
(14)

19−7/16
(494)

3 (76) Right
7 (178) Left

23−1/2
(597)
1 Bottom Return

SIDE VIEW
A

in.
14−1/2

mm,
368

in.
13−3/8

mm
340

in.
13

mm
330

in.
4−3/4

mm
121

SL280UH090V36B
SL280UH090V48B

17−1/2

446

16−3/8

416

406

6−1/4

159

SL280UH090V60C
SL280UH110V60C

533

19−7/8

504

19 1/2

495

203

SL280UH135V60D

24−1/2

622

23−3/8

546

584

9−3/4

248

SL280UH070V36A

Page 2

Parts Arrangement

HEAT EXCHANGER

COMBUSTION AIR INDUCER

COMBUSTION AIR INDUCER
PRESSURE SWITCH
ROLLOUT SWITCH GAS VALVE

CABINET

BURNER BOX
INNER BLOWER
ACCESS PANEL

SIGHT GLASS

CONTROL BOX
(Includes two−stage integrated control,
transformer and circuit breaker)

ACCESS PANEL

BLOWER
ASSEMBLY

FIGURE 1

Page 3

SL280UHV Gas Furnace

WARNING

The SL280UHV gas furnace is equipped with a two−stage,
variable speed integrated control. the control is compatible with:
Communicating thermostats − icomfort Touch®.
Non−comunicating thermostats − ComfortSense or other
conventional thermostats.
Control systems − Harmony III Zone Control System
(non−communicating).
Each SL280UHV unit is shipped ready for installation in
the upflow or horizontal position (left or right). The furnace
is shipped with the bottom panel in place. The bottom panel must be removed if the unit is to be installed in a horizontal application. The panel may also be removed in upflow
applications.

CAUTION
As with any mechanical equipment, personal injury
can result from contact with sharp sheet metal
edges. Be careful when you handle this equipment.
Certifications
SL280UHV units are CSA International certified to ANSI
Z21.47.
In the USA, installation of gas furnaces must conform with
local building codes. In the absence of local codes, units
must be installed according to the current National Fuel
Gas Code (ANSI-Z223.1). The National Fuel Gas Code is
available from the following address:
American National Standards Institute, Inc.
11 West 42nd Street
New York, NY 10036

Shipping and Packing List
Package 1 of 1 contains
1 − Assembled SL280UHV unit
1 − Bag assembly containing the following:
2 − Screws
1 − Snap bushing
1 − Snap plug
1 − Wire tie
1 − Vent warning label
1 − Owner’s manual and warranty card

Clearances
Adequate clearance must be made around the air openings into the vestibule area. In order to ensure proper unit
operation, combustion and ventilation air supply must be
provided according to the current National Fuel Gas Code.

The following items may be ordered separately:
1 − Thermostat
1 − Suspension Kit (for horizontal installations)
1 − Propane/LP changeover kit
1 − Return air base
1 − High altitude kit
1 − Side filter kit

Vent installations must be consistent with the venting
tables (in this instruction) and applicable provisions of local
building codes.

Check equipment for shipping damage. If you find any
damage, immediately contact the last carrier.

Safety Information

This furnace is CSA International certified for installation
clearances to combustible material as listed on the unit
nameplate and in the tables in figures 7 and 11. Accessibility
and service clearances must take precedence over fire
protection clearances.
NOTE − For installation on combustible floors, the furnace
shall not be installed directly on carpeting, tile, or other
combustible material other than wood flooring.
Installed Locations

DANGER
Danger of explosion.
There are circumstances in which odorant used with
LP/propane gas can lose its scent. In case of a leak,
LP/propane gas will settle close to the floor and may
be difficult to smell. An LP/propane leak detector
should be installed in all LP applications.

For installation in a residential garage, the furnace must
be installed so that the burner(s) and the ignition source
are located no less than 18 inches (457 mm) above the
floor. The furnace must be located or protected to avoid
physical damage by vehicles. When a furnace is installed
in a public garage, hangar, or other building that has a hazardous atmosphere, the furnace must be installed according to recommended good practice requirements and current National Fuel Gas Code.

Page 4

Temperature Rise
NOTE − Furnace must be adjusted to obtain a temperature
rise(high and low fire) within the range(s) specified on the unit
nameplate. Failure to do so may cause erratic limit operation
and may result in premature heat exchanger failure.
This SL280UHV furnace must be installed so that its electrical components are protected from water.
Installed in Combination with a Cooling Coil
When this furnace is used with cooling units, it shall be
installed in parallel with, or on the upstream side of, cooling
units to avoid condensation in the heating compartment.
See figure 1. With a parallel flow arrangement, a damper (or
other means to control the flow of air) must adequately prevent chilled air from entering the furnace. If the damper is
manually operated, it must be equipped to prevent operation
of either the heating or the cooling unit, unless it is in the full
HEAT or COOL setting. See figure 1.

The SL280UHV furnace may be installed in alcoves, closets, attics, basements, garages, and utility rooms in the upflow or horizontal position.
This furnace is not designed for installation in mobile
homes, recreational vehicles, or outdoors.
Never use an open flame to test for gas leaks. Check all
connections using a commercially available soap solution
made specifically for leak detection.

Use of Furnace as Construction Heater
Lennox does not recommend the use of SL280UHV units
as a construction heater during any phase of construction.
Very low return air temperatures, harmful vapors and operation of the unit with clogged or misplaced filters will damage the unit.
SL280UHV units may be used for heating of buildings or
structures under construction, if the following conditions
are met:

Heating Unit Installed Parallell to Air Handler Unit
Dampers
(open during heating operation only)

Gas Unit

Air Handler Unit

Dampers
(open during cooling operation only)

Heating Unit Installed Upstream of Cooling Unit

Gas Unit
Evaporator

FIGURE 1
When installed, this furnace must be electrically grounded
according to local codes. In addition, in the United States,
installation must conform with the current National Electric Code, ANSI/NFPA No. 70. The National Electric Code
(ANSI/NFPA No. 70) is available from the following address:
National Fire Protection Association
1 Battery March Park
Quincy, MA 02269

The vent system must be permanently installed per
these installation instructions.
A room thermostat must control the furnace. The use of
fixed jumpers that will provide continuous heating is not
allowed.
The return air duct must be provided and sealed to the
furnace.
Return air temperature range between 60°F (16°C) and
80°F (27°C) must be maintained.
Air filters must be installed in the system and must be
maintained during construction.
Air filters must be replaced upon construction completion.
The input rate and temperature rise must be set per the
furnace rating plate.
One hundred percent (100%) outdoor air must be provided for combustion air requirements during construction. Temporary ducting may supply outdoor air to the
furnace. Do not connect duct directly to the furnace.
Size the temporary duct following these instructions in
section for Combustion, Dilution and Ventilation Air in a
confined space with air from outside.
The furnace heat exchanger, components, duct system,
air filters and evaporator coils must be thoroughly
cleaned following final construction clean−up.
All furnace operating conditions (including ignition, input rate, temperature rise and venting) must be verified
according to these installation instructions.

General

NOTE − This furnace is designed for a minimum continuous return air temperature of 60°F (16°C) or an intermittent operation down to 55°F (13°C) dry bulb for cases
where a night setback thermostat is used. Return air temperature must not exceed 85°F (29°C) dry bulb.

These instructions are intended as a general guide and do
not supersede local codes in any way. Consult authorities
having jurisdiction before installation.
In addition to the requirements outlined previously, the following general recommendations must be considered
when installing a SL280UHV furnace:

Page 5

Place the furnace as close to the center of the air distribution system as possible. The furnace should also be
located close to the chimney or vent termination point.
Do not install the furnace where drafts might blow directly into it. This could cause improper combustion and unsafe operation.
Do not block the furnace combustion air openings with
clothing, boxes, doors, etc. Air is needed for proper
combustion and safe unit operation.
When the furnace is installed in an attic or other insulated space, keep insulation away from the furnace.
NOTE − The Commonwealth of Massachusetts stipulates these additional requirements:

D
D
D

needs and requirements for exhaust vents and gas piping.
A portion of this information has been reprinted with permission from the National Fuel Gas Code (ANSI-Z223.1).
This reprinted material is not the complete and official position of the ANSI on the referenced subject, which is represented only by the standard in its entirety.

CAUTION
Do not install the furnace in a corrosive or contaminated atmosphere. Meet all combustion and ventilation air requirements, as well as all local codes.

Gas furnaces shall be installed by a licensed plumber or fitter only.
The gas cock must be T handle" type.
When a furnace is installed in an attic, the passageway to and service area surrounding the equipment
shall be floored.

CAUTION
Insufficient combustion air can cause headaches,
nausea, dizziness or asphyxiation. It will also cause
excess water in the heat exchanger resulting in rusting and premature heat exchanger failure. Excessive
exposure to contaminated combustion air will result
in safety and performance related problems. Avoid
exposure to the following substances in the combustion air supply:
Permanent wave solutions
Chlorinated waxes and cleaners
Chlorine base swimming pool chemicals
Water softening chemicals
De-icing salts or chemicals
Carbon tetrachloride
Halogen type refrigerants
Cleaning solvents (such as perchloroethylene)
Printing inks, paint removers, varnishes, etc.
Hydrochloric acid
Cements and glues
Antistatic fabric softeners for clothes dryers
Masonry acid washing materials

WARNING
Product contains fiberglass wool.
Disturbing the insulation in this product during
installation, maintenance, or repair will expose you
to fiberglass wool. Breathing this may cause lung
cancer. (Fiberglass wool is known to the State of California to cause cancer.)
Fiberglass wool may also cause respiratory, skin,
and eye irritation.
To reduce exposure to this substance or for further
information, consult material safety data sheets
available from address shown below, or contact your
supervisor.
Lennox Industries Inc.
P.O. Box 799900
Dallas, TX 75379−9900

Combustion, Dilution & Ventilation Air
In the past, there was no problem in bringing in sufficient outdoor air for combustion. Infiltration provided all the air that
was needed. In today’s homes, tight construction practices
make it necessary to bring in air from outside for combustion. Take into account that exhaust fans, appliance vents,
chimneys, and fireplaces force additional air that could be
used for combustion out of the house. Unless outside air is
brought into the house for combustion, negative pressure
(outside pressure is greater than inside pressure) will build
to the point that a downdraft can occur in the furnace vent
pipe or chimney. As a result, combustion gases enter the living space creating a potentially dangerous situation.
In the absence of local codes concerning air for combustion and ventilation, use the guidelines and procedures in
this section to install SL280UHV furnaces to ensure efficient and safe operation. You must consider combustion air

All gas-fired appliances require air for the combustion process. If sufficient combustion air is not available, the furnace or other appliances will operate inefficiently and unsafely. Enough air must be provided to meet the needs of all
fuel-burning appliances and appliances such as exhaust
fans which force air out of the house. When fireplaces, exhaust fans, or clothes dryers are used at the same time as
the furnace, much more air is necessary to ensure proper
combustion and to prevent a downdraft. Insufficient air
causes incomplete combustion which can result in carbon
monoxide.
In addition to providing combustion air, fresh outdoor air
dilutes contaminants in the indoor air. These contaminants may include bleaches, adhesives, detergents, solvents and other contaminants which can corrode furnace
components.
The requirements for providing air for combustion and ventilation depend largely on whether the furnace is installed in
an unconfined or a confined space.

Page 6

Unconfined Space
An unconfined space is an area such as a basement or
large equipment room with a volume greater than 50 cubic
feet (1.42 m3) per 1,000 Btu (.29 kW) per hour of the combined input rating of all appliances installed in that space.
This space also includes adjacent rooms which are not
separated by a door. Though an area may appear to be unconfined, it might be necessary to bring in outdoor air for
combustion if the structure does not provide enough air by
infiltration. If the furnace is located in a building of tight
construction with weather stripping and caulking around
the windows and doors, follow the procedures in the air
from outside section.
Confined Space
A confined space is an area with a volume less than 50 cubic feet (1.42 m3) per 1,000 Btu (.29 kW) per hour of the
combined input rating of all appliances installed in that
space. This definition includes furnace closets or small
equipment rooms.
When the furnace is installed so that supply ducts carry air
circulated by the furnace to areas outside the space containing the furnace, the return air must be handled by ducts
which are sealed to the furnace casing and which terminate
outside the space containing the furnace. This is especially
important when the furnace is mounted on a platform in a
confined space such as a closet or small equipment room.
Even a small leak around the base of the unit at the platform
or at the return air duct connection can cause a potentially
dangerous negative pressure condition. Air for combustion
and ventilation can be brought into the confined space either
from inside the building or from outside.
EQUIPMENT IN CONFINED
SPACE ALL AIR FROM INSIDE

CHIMNEY
OR GAS
VENT

WATER
HEATER
FURNACE

Air from Inside
If the confined space that houses the furnace adjoins a
space categorized as unconfined, air can be brought in by
providing two permanent openings between the two
spaces. Each opening must have a minimum free area of 1
square inch (645 mm2) per 1,000 Btu (.29 kW) per hour of
total input rating of all gas−fired equipment in the confined
space. Each opening must be at least 100 square inches
(64516 mm2). One opening shall be within 12 inches (305
mm) of the top of the enclosure and one opening within 12
inches (305 mm) of the bottom. See figure 2.
Air from Outside
If air from outside is brought in for combustion and ventilation, the confined space must have two permanent openings. One opening shall be within 12 inches (305 mm) of the
top of the enclosure and one opening within 12 inches (305
mm) of the bottom. These openings must communicate directly or by ducts with the outdoors or spaces (crawl or attic) that freely communicate with the outdoors or indirectly
through vertical ducts. Each opening shall have a minimum
free area of 1 square inch (645 mm2) per 4,000 Btu (1.17
kW) per hour of total input rating of all equipment in the enclosure. See figures 3 and 4. When communicating with
the outdoors through horizontal ducts, each opening shall
have a minimum free area of 1 square inch (645 mm2) per
2,000 Btu (.56 kW) per total input rating of all equipment in
the enclosure. See figure 5.
When ducts are used, they shall be of the same cross−sectional area as the free area of the openings to which they
connect. The minimum dimension of rectangular air ducts
shall be no less than 3 inches (75 mm). In calculating free
area, the blocking effect of louvers, grilles, or screens must
be considered. If the design and free area of protective covering is not known for calculating the size opening required,
it may be assumed that wood louvers will have 20 to 25 percent free area and metal louvers and grilles will have 60 to
75 percent free area. Louvers and grilles must be fixed in the
open position or interlocked with the equipment so that they
are opened automatically during equipment operation.

OPENINGS
(To Adjacent
Room)
AIR FLOW

NOTE − Each opening shall have a free area of at least one square
inch (645 mm 2) per 1,000 Btu (.29 kW) per hour of the total input rating of all equipment in the enclosure, but not less than 100 square
inches (64516 mm 2).

FIGURE 2

Page 7

EQUIPMENT IN CONFINED SPACE
ALL AIR FROM OUTSIDE
(Inlet Air from Crawlspace and Outlet Air to Ventilated Attic)
CHIMNEY OR
GAS VENT

VENTILATION LOUVERS
(Each end of attic)

OUTLET
AIR

FURNACE

WATER
HEATER

INLET
AIR

VENTILATION
LOUVERS
(For unheated crawl space)

AIR FLOW

NOTE−The inlet and outlet air openings shall each have a free area of at least one square inch (645
mm2) per 4,000 Btu (1.17 kW) per hour of the total input rating of all equipment in the enclosure.

FIGURE 3

CHIMNEY
OR GAS
VENT

EQUIPMENT IN CONFINED SPACE
ALL AIR FROM OUTSIDE
(All Air Through Ventilated Attic)

CHIMNEY
OR GAS
VENT

VENTILATION LOUVERS
(Each end of attic)

EQUIPMENT IN
CONFINED SPACE
ALL AIR FROM
OUTSIDE
WATER
HEATER

OUTLET AIR

OUTLET
AIR

FURNACE
FURNACE

INLET AIR
(Ends 12 in.
above bottom)
INLET AIR
AIR FLOW

WATER
HEATER
AIR FLOW

NOTE − Each air duct opening shall have a free area of at least
one square inch (645 mm 2) per 2,000 Btu (.59 kW) per hour of
the total input rating of all equipment in the enclosure. If the
equipment room is located against an outside wall and the air
openings communicate directly with the outdoors, each opening shall have a free area of at least one square inch (645 mm2)
per 4,000 Btu (1.17 kW) per hour of the total input rating of all
other equipment in the enclosure.

NOTE−The inlet and outlet air openings shall each have a
free area of at least one square inch (645 mm 2) per 4,000
Btu (1.17 kW) per hour of the total input rating of all equipment in the enclosure.

FIGURE 4

FIGURE 5

Page 8

Upflow Applications
Allow for clearances to combustible materials as indicated
on the unit nameplate. Minimum clearances for closet or alcove installations are shown in figure 7.

Setting Equipment

WARNING
Do not install the furnace on its front or its back. Do
not connect the return air ducts to the back of the furnace. Doing so will adversely affect the operation of
the safety control devices, which could result in personal injury or death.
The SL280UHV gas furnace can be installed as shipped
in either the upflow position or the horizontal position.
Select a location that allows for the required clearances
that are listed on the unit nameplate. Also consider gas
supply connections, electrical supply, vent connection,
and installation and service clearances [24 inches (610
mm) at unit front]. The unit must be level.
NOTE − Units with 1/2 hp blower motors are equipped with
three flexible legs and one rigid leg. See figure 6. The rigid
leg is equipped with a shipping bolt and a flat white plastic
washer (rather than the rubber mounting grommet used
with a flexible mounting leg). The bolt and washer must
be removed before the furnace is placed into operation. After the bolt and washer have been removed, the rigid leg will not touch the blower housing.
SL280UHV07036A and
SL280UHV09036B WITH 1/2 HP
BLOWER MOTOR

Upflow Application Installation Clearances
Top

Left Side

Right Side

AIR FLOW

Bottom
Type of Vent
Connector

Type C

Type B1

Top

1 in. (25 mm)

*Front

2−1/4 in. (57 mm)**

2−1/4 in. (57 mm)

Back

Sides

0†

Vent

6 in. (152 mm)

1 in. (25 mm)

Floor

0‡

*Front clearance in alcove installation must be 24 in. (610 mm).
Maintain a minimum of 24 in. (610 mm) for front service access.
** 3−1/4 in. if single wall vent pipe is used.
‡For installation on a combustible floor, do not install the furnace
directly on carpeting, tile or other combustible materials other
than wood flooring.
†Left side requires 3 inches if a single wall vent is used on 14−1/2
inch cabinets, or 2 in. if a single wall vent is used on 17−1/2 in. cabinets.

RIGID LEG
remove shipping bolt and washer

FIGURE 7

FIGURE 6

Page 9

Return Air −− Upflow Applications
Single Side Return Air
(with transition and filter)

Return air can be brought in through the bottom or either
side of the furnace installed in an upflow application. If the
furnace is installed on a platform with bottom return, make
an airtight seal between the bottom of the furnace and the
platform to ensure that the furnace operates properly and
safely. The furnace is equipped with a removable bottom
panel to facilitate installation.

20” X 25” X 1”
(508mm X635mm X 25mm)
Cleanable Filter

Markings are provided on both sides of the furnace cabinet
for installations that require side return air. Cut the furnace
cabinet at the maximum dimensions shown on page 2.
NOTE − 60C and 60D units that require air volumes over 1800
cfm (850 L/s) must have one of the following:

Return Air
Plenum

1 − Return air from single side with transition which will
accommodate 20 x 25 x 1 in. (508 x 635 x 25 mm) cleanable air filter. (Required to maintain proper air velocity.)
See figure 8.

AIR FLOW

2 − Return air from single side with optional RAB Return
Air Base. See figure 9.

Transition

3 − Return air from bottom and one side.
4 − Return air from both sides.
5 − Return air from bottom.

FIGURE 8

Refer to Engineering Handbook for additional information.
Optional Return Air Base
(Upflow Applications Only −− For use with A, B, C and D cabinets)
FURNACE
FRONT

INDOOR AIR

AIR FLOW

IF BASE
IS USED
WITHOUT
IAQ CABINET,
A SINGLE
RETURN AIR
PLENUM
MUST
COVER BOTH
UNIT AND
RETURN
AIR BASE
OPENINGS

3−1/4
(83)

7−1/4
(184)

1 23

(584)
Overall
(Maximum)

Minimum
11 (279)
2 Maximum
1 Unit side return air
14 (356)
Opening

5−5/8
(143)

22−7/16
(570)
Overall
(Maximum)

SIDE RETURN
AIR OPENINGS
(Either Side)
23
(584)
26−7/8
(683)

OPTIONAL
14−1/2” (368) A Width (65W75)
17−1/2” (446) B Width (50W98) RETURN AIR BASE
21”− (533) C Width (50W99)
24−1/2”− (622) D Width (51W00)

3/4
(19)

SIDE VIEW

NOTE− Optional Side Return Air Filter Kits are not for use with Optional Return Air Base.
1 Both the unit return air opening and the base return air opening must be covered by a single plenum or IAQ cabinet.
Minimum unit side return air opening dimensions for units requiring 1800 cfm or more of air (W x H): 23 x 11 in. (584 x 279 mm).
The opening can be cut as needed to accommodate plenum or IAQ cabinet while maintaining dimensions shown.
Side return air openings must be cut in the field. There are cutting guides stenciled on the cabinet for the side return air
opening. The size of the opening must not extend beyond the markings on the furnace cabinet.
2 To minimize pressure drop, the largest opening height possible (up to 14 inches) is preferred.

FIGURE 9

Page 10

Removing the Bottom Panel
Remove the two screws that secure the bottom cap to the
furnace. Pivot the bottom cap down to release the bottom
panel. Once the bottom panel has been removed, reinstall
the bottom cap. See figure 10.
Removing the Bottom Panel

Horizontal Applications
The SL280UHV furnace can be installed in horizontal applications. Order kit number 51W10 (or use equivalent)
from Lennox.
Allow for clearances to combustible materials as indicated
on the unit nameplate. Minimum clearances for closet or alcove installations are shown in figure 11.
This furnace may be installed in either an attic or a crawlspace. Either suspend the furnace from roof rafters or
floor joists, as shown in figure 12, or install the furnace on a
platform, as shown in figure 13.
Typical Horizontal Application
Unit Suspended in Attic or Crawlspace

Bracket
Metal Strap
Bottom Cap

3/16 inch
Air Flow

Screw

Bottom Cap
FIGURE 12
NOTE − Heavy−gauge perforated sheet metal straps may
be used to suspend the unit from roof rafters or ceiling
joists. When straps are used to suspend the unit in this
way, support must be provided for both the ends. The
straps must not interfere with the plenum or exhaust piping installation. Cooling coils and supply and return air
plenums must be supported separately.
NOTE − When the furnace is installed on a platform in a
crawlspace, it must be elevated enough to avoid water
damage and to allow the evaporator coil to drain.
Return Air −− Horizontal Applications

Bottom Panel
FIGURE 10

AIR FLOW

Horizontal Application
Installation Clearances
Top

Left
End

Right
End

Bottom
Vent Connector
Type

Type C

Type B1

Top

*Front

2−1/4 in. (57 mm)**

2−14 in. (57 mm)

Back

Ends

2 in. (51 mm)

Vent

6 in. (152 mm)

1 in. (25 mm)

Floor

0‡

Return air must be brought in through the end of a furnace
installed in a horizontal application. The furnace is
equipped with a removable bottom panel to facilitate
installation. See figure 10.

FIGURE 11

Page 11

TABLE 1

Horizontal Application
Unit Installed on Platform

Furnace
Cabinet Width

Line contact is permissible
See the unit nameplate for
clearances.

GAS
ENTRY

14−1/2"
17−1/2"
21"
24−1/2"
VENT
PIPE

Filter Size
Side Return
Bottom Return
16 X 25 X 1 (1)
16 X 25 X 1 (1)
16 X 25 X 1 (1)
16 X 25 X 1 (2)

14 X 25 X 1 (1)
16 X 25 X 1 (1)
20 X 25 X 1 (1)
24 X 25 X 1 (1)

Duct System
Use industry-approved standards (such as those published by Air Conditioning Contractors of America or American Society of Heating, Refrigerating and Air Conditioning
Engineers) to size and install the supply and return air duct
system. This will result in a quiet and low-static system that
has uniform air distribution.
NOTE − Do not operate the furnace in the heating mode
with an external static pressure that exceeds 0.8 inches
w.c. Higher external static pressures may cause erratic limit operation.
Supply Air Plenum

SERVICE PLATFORM

FIGURE 13

WARNING
Improper installation of the furnace can result in personal injury or death. Combustion and flue products
must never be allowed to enter the return air system
or the living space. Use screws and joint tape to seal
the return air system to the furnace.
In platform installations with bottom return air, the
furnace should be sealed airtight to the return air plenum. A door must never be used as a portion of the
return air duct system. The base must provide a
stable support and an airtight seal to the furnace. Allow absolutely no sagging, cracks, gaps, etc.
The return and supply air duct systems must never
be connected to or from other heating devices such
as a fireplace or stove, etc. Fire, explosion, carbon
monoxide poisoning, personal injury and/or property damage could result.

WARNING
The inner blower panel must be securely in place
when the blower and burners are operating. Gas
fumes, which could contain carbon monoxide, can
be drawn into living space resulting in personal injury or death.

Filters
This unit is not equipped with a filter or rack. A field−provided high−velocity filter is required for the unit to operate
properly. Table 1 lists recommended filter sizes.
A filter must be in place any time the unit is operating.

If the furnace is installed without a cooling coil, a removable
access panel must be installed in the supply air duct. The
access panel should be large enough to permit inspection
(either by smoke or reflected light) of the heat exchanger
for leaks after the furnace is installed. The furnace access
panel must always be in place when the furnace is operating and it must not allow leaks into the supply air duct system.
Return Air Plenum
NOTE − Return air must not be drawn from a room
where this furnace, or any other gas−fueled appliance
(i.e., water heater), or carbon monoxide− producing device (i.e., wood fireplace) is installed.
When return air is drawn from a room, a negative pressure is created in the room. If a gas appliance is operating
in a room with negative pressure, the flue products can
be pulled back down the vent pipe and into the room. This
reverse flow of the flue gas may result in incomplete combustion and the formation of carbon monoxide gas. This
toxic gas might then be distributed throughout the house
by the furnace duct system.
In upflow applications, the return air can be brought in
through the bottom or either side of the furnace. If a furnace with bottom return air is installed on a platform, make
an airtight seal between the bottom of the furnace and the
platform to ensure that the unit operates properly and
safely. Use fiberglass sealing strips, caulking, or equivalent sealing method between the plenum and the furnace
cabinet to ensure a tight seal. If a filter is installed, size the
return air duct to fit the filter frame.

Page 12

Venting
A 4−inch diameter flue transition is factory-installed on the
combustion air inducer outlet of all models. Figure 15
shows the combustion air inducer as shipped from the
factory.
Mounting Screws Location
mounting screws

1 − Remove the four mounting screws (figure 14) which
secure the combustion air inducer / pressure switch
assembly to the orifice plate. Lift and rotate the assembly 90 degrees clockwise or counter clockwise to either
the 3 o’clock position or to 9 o’clock position and re−secure with four screws. Gasket should be left in place.
2 − Use tin snips to cut preferred opening on the cabinet
for repositioning the flue outlet. Use the cut out piece
as a cover plate to patch unused opening on cabinet.
UPFLOW POSITION
Left Side Vent Discharge
collector box

cover plate

pressure
switch
vent pipe

make−up
box

mounting screw
FIGURE 14

UPFlow Position

flue
transition

UPFLOW POSITION
Top Vent Discharge
vent pipe
flue
transition

AIR

collector box

pressure
switch

make−up
box

FLOW

Gas supply piping must be brought into the unit from the right
side in order to accommodate the flue pipe.
Remove make−up box assembly (2 screws) and cut wire tie to
free make−up box wires. Re−install make−up box on other side
of cabinet.
Re−secure make−up box wires, either pulling excess wires
through the blower compartment and securing with supplied
wire tie, or coil excess wire and secure to the gas manifold.

FIGURE 16
UPFLOW POSITION
Right Side Vent Discharge
cover plate
flue transition

collector box

vent pipe
pressure
switch
AIR

FLOW

FIGURE 15

IMPORTANT
The unit will not vent properly with the flue transition
pointed down in the 6 o’clock position.
The combustion air inducer may be rotated clockwise or counterclockwise by 90° to allow for top or
side vent discharge in all applications. When the unit
is installed, the flue transition must be in the 9
o’clock, 12 o’clock or 3 o’clock position.
If necessary reposition the combustion air inducer, pressure switch and or make up box as needed per the following steps and see figures 15 through 21.
Page 13

make−up
box

AIR

FLOW

Pressure switch tubing may be too long. Cut to
fit , then re−attach to barbed fitting on pressure
switch. Tubing must not be allowed to sag.

FIGURE 17

Horizontal Position
HORIZONTAL RIGHT POSITION

HORIZONTAL LEFT POSITION

Top Vent Discharge

Top Vent Discharge
vent pipe

vent pipe

pressure switch

flue transition

cover plate
flue
transition

AIR

FLOW

collector box
cover plate

make−up box
collector box
Disconnect pressure switch hose from barbed fitting on the pressure switch assembly. Remove pressure switch assembly (1
screw) and cut wire tie to free pressure switch wires. Re−install
pressure switch on the other side of orifice plate and re−connect
pressure switch hose.
Re−secure pressure switch wires by either pulling excess wires
through the blower compartment and securing with supplied wire
tie or coil excess wire and secure to the gas manifold.

FIGURE 18

make−up box
Gas supply piping must be brought into the unit from the bottom
in order to accommodate the flue pipe.
Remove make−up box assembly (2 screws) and cut wire tie to
free make−up box wires. Re−install make−up box on other side
of cabinet.
Re−secure make−up box wires by either pulling excess wires
through the blower compartment and securing with supplied
wire tie, or coil excess wire and secure to the gas manifold.

FIGURE 20

HORIZONTAL LEFT POSITION
Side Vent Discharge
pressure switch

HORIZONTAL RIGHT POSITION
Side Vent Discharge
pressure switch

AIR
FLOW
AIR

flue transition

FLOW

make−up box

flue transition

collector box
collector box

Disconnect pressure switch hose from barbed fitting on the
pressure switch assembly. Remove pressure switch assembly
(1 screw) and cut wire tie to free pressure switch wires. Re−
install pressure switch on the other side of orifice plate and re−
connect pressure switch hose.
Re−secure pressure switch wires by either pulling excess wires
through the blower compartment and securing with supplied
wire tie, or coil excess wire and secure to the gas manifold.

make up box

FIGURE 21

FIGURE 19

Page 14

The SL280UHV series units are classified as fan−assisted
Category I furnaces when vertically vented according to
the latest edition of National Fuel Gas Code (NFPA 54 /
ANSI Z223.1) in the USA. A fan−assisted Category I furnace is an appliance equipped with an integral mechanical
means to either draw or force combustion products through
the combustion chamber and/or heat exchanger. The
SL280UHV is not approved for use with horizontal venting..
NOTE − Use these instructions as a guide. They do not supersede local codes. This furnace must be vented according to all local codes these installation instructions, and the
provided venting tables in these instructions
The venting tables in this manual were extracted from the
National Fuel Gas Code (NFPA 54 / ANSI Z223.1) and are
provided as a guide for proper vent installation. Proper application, termination, construction and location of vents
must conform to local codes having jurisdiction. In the absence of local codes, the NFGC serves as the defining document.
Refer to the tables and the venting information contained in
these instructions to properly size and install the venting
system.

IMPORTANT
Once the venting system is installed, attach the Disconnected Vent" warning sticker to a visible area of
the plenum near the vent pipe. See figure 22. The
warning sticker is provided in the bag assembly. Order kit 66W04 for additional stickers.

Use self−drilling sheet metal screws or a mechanical fastener to firmly secure the vent pipe to the round collar of the
flue transition. If self−drilling screws are used to attach the
vent pipe, it is recommended that three be used. Drive one
self−drilling screw through the front and one through each
side of the vent pipe and collar. See figures 19, 21 and 22.
Install the first vent connector elbow at a minimum of six
inches (152 mm) from the furnace vent outlet. See figure
22.
Venting Using a Masonry Chimney
The following additional requirements apply when a lined
masonry chimney is used to vent this furnace.
Masonry chimneys used to vent Category I central furnaces must be either tile-lined or lined with a listed metal
lining system or dedicated gas vent. Unlined masonry
chimneys are prohibited. See figures 23 and 24 for common venting.
A chimney with one or more sides exposed to the outside of
the structure is considered to be an exterior chimney.
An exterior masonry chimney that is not tile−lined must be
lined with B1 vent or a listed insulated flexible metal vent.
An exterior tile−lined chimney that is sealed and capped
may be lined with a listed uninsulated flexible metal vent.
If the existing chimney will not accommodate a listed metal
liner, either the chimney must be rebuilt to accommodate
one of these liners or an alternate approved venting method must be found.
Insulation for the flexible vent pipe must be an encapsulated fiberglass sleeve recommended by the flexible vent
pipe manufacturer. See figure 23.
Common Venting Using Metal−Lined Masonry Chimney

WARNING

SEALED

Asphyxiation hazard. The exhaust vent for this furnace must be securely connected to the furnace flue
transition at all times.
VENT CONNECTION

“DISCONNECTED VENT”
WARNING
STICKER

5 ft. (1.5 m)
minimum

MAX. LENGTH
−− SEE NOTE 1
BELOW.
MIN. LENGTH −− AS
SHORT AS PRACTICAL

EXTERIOR
CHIMNEY WITH
METAL
LINER

VENT CONNECTOR
4 in. (102 mm)
minimum

VENT PIPE
(min. 6" length)

FURNACE

OTHER
APPLIANCE
PERMANENTLY
SEALED FIREPLACE
OPENING
AIR FLOW

FLUE TRANSITION
COLLAR

NOTE 1 − Refer to the provided venting tables for installations. Refer
to the capacity requirements shown in the provided venting tables.

FIGURE 23
FIGURE 22

Page 15

Common Venting Using Tile−Lined Interior Masonry Chimney and Combined Vent Connector
MINIMUM LENGTH = AS SHORT AS PRACTICAL.
FOR MAXIMUM LENGTH SEE NOTE TO LEFT

INTERIOR TILE−LINED
MASONRY CHIMNEY

NOTE− Refer to provided venting tables
for installations.
NOTE − the chimney must be properly
sized per provided venting tables or
lined with listed metal lining system.
VENT
CONNECTOR
OTHER
APPLIANCE

PERMANENTLY
SEALED FIREPLACE
OPENING
FURNACE
AIR FLOW

FIGURE 24
Never connect a Category I appliance to a chimney that is
DO NOT insulate the space between the liner and the
servicing a solid−fuel appliance. If a fireplace chimney flue
chimney wall with puffed mica or any other loose granis used to vent this appliance, the fireplace opening must
ular insulating material
be permanently sealed.
A type B or listed chimney lining system that passes
through an unused masonry chimney flue is not considered
to be exposed to the outdoors.
SINGLE appliance venting of a fan-assisted furnace
into a tile-lined masonry chimney (interior or outside
General Venting Requirements
wall) is PROHIBITED. The chimney must first be lined
Vent all SL280UHV furnaces according to these instrucwith either type B1 vent or an insulated single wall
tions:
flexible vent lining system which has been sized ac1 − Vent diameter recommendations and maximum allowcording to the provided venting tables and the vent
able piping runs are found in the provided venting
pipe manufacturer’s instructions.
tables.
A fan−assisted furnace may be commonly vented into an
2 − In no case should the vent or vent connector diameter
existing lined masonry chimney if the following conditions
be less than the diameter specified in the provided
are met:
venting tables.
The chimney is currently serving at least one drafthood
3 − The minimum vent capacity determined by the sizing
equipped appliance
tables must be less than the low fire input rating and the
The vent connectors and chimney are sized according
maximum vent capacity must be greater than the high
to the provided venting tables.
fire input rating.
If type B1 double-wall vent is used inside a chimney, no oth4 − Single appliance vents − If the vertical vent or tile-lined
er appliance can be vented into the chimney. The outer wall
chimney has a larger diameter or flow area than the
of type B1 vent pipe must not be exposed to flue products.
vent connector, use the vertical vent diameter to deA type B1 vent or masonry chimney liner shall terminate
termine the minimum vent capacity and the vent
above the roof surface with a listed cap or a listed roof asconnector
diameter to determine the maximum vent
sembly according to the terms of their respective listings
capacity.
The
flow area of the vertical vent, however,
and the vent manufacturer’s instructions.
shall
not
exceed
7 times the flow area of the listed apWhen inspection reveals that an existing chimney is not
pliance categorized vent area, drafthood outlet area or
safe for the intended purpose, it shall be rebuilt to conform
flue collar area unless designed according to approved
to nationally recognized standards, lined or relined with
engineering methods.
suitable materials, or replaced with a gas vent or chimney
suitable for venting SL280UHV series units. The chimney
5 − Multiple appliance vents − The flow area of the largest
passageway must be checked periodically to ensure that it
section of vertical vent or chimney shall not exceed 7
is clear and free of obstructions.
times the smallest listed appliance categorized vent
area, drafthood outlet area or flue collar area unless deDo not install a manual damper, barometric draft regulator,
signed according to approved engineering methods.
or flue restrictor between the furnace and the chimney.

IMPORTANT

Page 16

6 − The entire length of single wall metal vent connector
shall be readily accessible for inspection, cleaning,
and replacement.
7 − Single appliance venting configurations with zero lateral lengths (tables 3 and 4) are assumed to have no
elbows in the vent system. For all other vent configurations, the vent system is assumed to have two 90° elbows. For each additional 90° elbow or equivalent (for
example two 45° elbows equal one 90° elbow) beyond
two, the maximum capacity listed in the venting table
should be reduced by 10% (0.90 x maximum listed capacity).
8 − The common venting tables (5, 6, 7, and 8) were generated using a maximum horizontal vent connector
length of 1−1/2 feet (.46 m) for each inch (25 mm) of
connector diameter as follows:
TABLE 2
Connector Diameter
inches (mm)

Maximum Horizontal
Connector Length feet (m)

3 (76)

4−1/2 (1.37)

4 (102)

6 (1.83)

5 (127)

7−1/2 (2.29)

6 (152)

9 (2.74)

7 (178)

10−1/2 (3.20)

9 − If the common vertical vent is offset, the maximum
common vent capacity listed in the common venting
tables should be reduced by 20%, the equivalent of two
90° elbows (0.80 x maximum common vent capacity).
The horizontal length of the offset shall not exceed
1-1/2 feet (.46 m) for each inch (25 mm) of common
vent diameter.
10 − The vent pipe should be as short as possible with the
least number of elbows and angles required to complete the job. Route the vent connector to the vent using the shortest possible route.
11 − A vent connector shall be supported without any dips
or sags and shall slope a minimum of 1/4 inch (6.4 mm)
per linear foot (305 mm) of connector, back toward the
appliance.
12 − Vent connectors shall be firmly attached to the furnace

flue collar by self−drilling screws or other approved
means, except vent connectors of listed type B vent
material which shall be assembled according to the
manufacturer’s instructions. Joints between sections
of single wall connector piping shall be fastened by
screws or other approved means.
13 − When the vent connector used for Category I appliances must be located in or pass through a crawlspace, attic or other areas which may be cold, that portion of the vent connector shall be constructed of listed
double-wall type B vent material or material having
equivalent insulation qualities.
14 − All venting pipe passing through floors, walls, and ceilings must be installed with the listed clearance to combustible materials and be fire stopped according to local codes. In absence of local codes, refer to NFGC
(Z223.1).
15 − No portion of the venting system can extend into, or pass
through any circulation air duct or plenum.
16 − Vent connectors serving Category I appliances shall
not be connected to any portion of mechanical draft
systems operating under positive pressure such as
Category III or IV venting systems.
17 − If vent connectors are combined prior to entering the
common vent, the maximum common vent capacity
listed in the common venting tables must be reduced by
10%, the equivalent of one 90° elbow (0.90 x maximum
common vent capacity).
18 − The common vent diameter must always be at least as
large as the largest vent connector diameter.
19 − In no case, shall the vent connector be sized more than
two consecutive table size diameters over the size of
the draft hood outlet or flue collar outlet.
20 − Do not install a manual damper, barometric draft regulator or flue restrictor between the furnace and the
chimney.
21 − When connecting this appliance to an existing dedicated or common venting system, you must inspect the
venting system’s general condition and look for signs
of corrosion. The existing vent pipe size must conform
to these instructions and the provided venting tables. If
the existing venting system does not meet these requirements, it must be resized.

Page 17

TABLE 3
Capacity of Type B Double−Wall Vents with Type B Double−Wall Connectors
Serving a Single Category I Appliance
Vent and Connector Diameter − D (inches)
Height
H
(feet)

Lateral
L
(feet)

3 Inch

4 Inch

5 Inch

6 Inch

Appliance Input Rating in Thousands of Btu Per Hour
MIN

MAX

MIN

MAX

MIN

MAX

MIN

MAX

152

251

375

157

232

153

227

149

223

165

276

415

109

178

263

103

171

255

164

247

175

295

447

118

194

289

113

187

280

104

176

267

191

327

502

136

226

339

130

219

330

121

206

315

112

195

301

202

349

540

149

250

377

143

242

367

133

229

351

124

217

337

116

206

322

100

213

374

587

166

283

432

160

275

421

150

262

405

141

249

389

132

237

374

113

214

104

346

NOTE − Single appliance venting configurations with zero lateral lengths are assumed to have no elbows in the vent system. For all other
vent configurations, the vent system is assumed to have two 90° elbows. For each additional 90° elbow or equivalent (for example two 45°
elbows equal one 90° elbow) beyond two, the maximum capacity listed in the venting table should be reduced by 10 percent (0.90 x maximum listed capacity).

Page 18

TABLE 4
Capacity of Type B Double−Wall Vents with Single−Wall Metal Connectors
Serving a Single Category I Appliance
Vent and Connector Diameter − D (inches)
Height
H
(feet)

Lateral
L
(feet)

3 Inch

4 Inch

5 Inch

6 Inch

Appliance Input Rating in Thousands of Btu Per Hour
MIN

MAX

MIN

MAX

MIN

MAX

MIN

MAX

151

249

126

373

156

123

231

102

152

146

225

114

147

163

220

164

273

123

412

108

176

121

261

102

107

168

151

252

122

161

175

243

174

293

120

444

117

193

119

287

111

105

185

148

277

100

132

171

188

261

190

325

116

499

136

225

115

337

128

102

216

144

326

116

128

201

182

308

158

186

220

290

200

346

114

537

148

248

113

375

140

100

239

141

363

129

125

223

177

344

155

208

216

325

186

192

254

306

211

372

110

584

164

281

109

429

157

271

136

417

144

122

255

171

397

115

131

151

239

208

377

181

223

246

357

Page 19

TABLE 5
Vent Connector Capacity
Type B Double−Wall Vents with Type B Double−Wall Connectors
Serving Two or More Category I Appliances
Vent
Height
H
(feet)

Vent and Connector Diameter − D (inches)

Connector
Rise
R
(feet)

3 Inch

4 Inch

5 Inch

6 Inch

Appliance Input Rating in Thousands of Btu Per Hour
MIN

MAX

MIN

MAX

MIN

MAX

MIN

MAX

106

164

121

183

132

199

114

176

128

195

139

210

123

189

136

206

146

220

142

220

153

235

102

163

248

157

246

105

167

259

110

176

271

113

181

288

118

190

299

123

198

309

TABLE 6
Common Vent Capacity
Type B Double−Wall Vents with Type B Double−Wall Connectors
Serving Two or More Category I Appliances
Vent
Height
H
(feet)

Common Vent Diameter − D (inches)
4 Inch

5 Inch

6 Inch

7 Inch

Appliance Input Rating in Thousands of Btu Per Hour
FAN + FAN

FAN + NAT

FAN + FAN

FAN + NAT

FAN + FAN

FAN + NAT

FAN + FAN

FAN + NAT

101

140

116

204

161

309

248

155

129

224

178

339

110

275

169

141

243

194

367

299

15
20

125

112

195

164

283

228

427

352

136

123

215

183

314

255

475

394

152

138

244

210

361

297

547

459

Page 20

TABLE 7
Vent Connector Capacity
Type B Double−Wall Vents with Single−Wall Metal Connectors
Serving Two or More Category I Appliances
Vent and Connector Diameter − D (inches)
Height
H
(feet)

Lateral
L
(feet)

3 Inch

4 Inch

5 Inch

6 Inch

Appliance Input Rating in Thousands of Btu Per Hour
MIN

MAX

MIN

MAX

MIN

MAX

MIN

MAX
NR

168

182

121

131

175

198

125

126

184

193

130

138

191

208

119

121

182

186

124

134

189

203

129

144

197

217

116

138

177

214

121

150

185

230

100

127

160

193

243

115

152

175

238

103

120

163

182

252

107

125

172

190

264

110

112

175

169

278

115

117

185

177

290

119

122

193

185

300

TABLE 8
Common Vent Capacity
Type B Double−Wall Vents with Single−Wall Metal Connectors
Serving Two or More Category I Appliances
Vent
Height
H
(feet)

Common Vent Diameter − D (inches)
4 Inch

5 Inch

6 Inch

7 Inch

Appliance Input Rating in Thousands of Btu Per Hour
FAN + FAN

FAN + NAT

FAN + FAN

FAN + NAT

FAN + FAN

FAN + NAT

FAN + FAN

FAN + NAT

113

200

158

304

244

126

218

173

331

269

163

137

237

189

357

292

121

108

189

159

275

221

416

343

131

118

208

177

305

247

463

383

145

132

236

202

350

286

533

446

Page 21

Removal of the Furnace from Common Vent
In the event that an existing furnace is removed from a
venting system commonly run with separate gas appliances, the venting system is likely to be too large to
properly vent the remaining attached appliances.
Conduct the following test while each appliance is operating and the other appliances (which are not operating) remain connected to the common venting system. If the
venting system has been installed improperly, you must
correct the system as indicated in the general venting requirements section.

WARNING

3 − Close all building doors and windows and all doors between the space in which the appliances remaining
connected to the common venting system are located
and other spaces of the building. Turn on clothes dryers and any appliances not connected to the common
venting system. Turn on any exhaust fans, such as
range hoods and bathroom exhausts, so they will operate at maximum speed. Do not operate a summer exhaust fan. Close fireplace dampers.
4 − Follow the lighting instructions. Turn on the appliance
that is being inspected. Adjust the thermostat so that
the appliance operates continuously.
5 − After the main burner has operated for 5 minutes, test
for leaks of flue gases at the draft hood relief opening.
Use the flame of a match or candle, or smoke from a
cigarette, cigar, or pipe.

CARBON MONOXIDE POISONING HAZARD
Failure to follow the steps outlined below for each
appliance connected to the venting system being
placed into operation could result in carbon monoxide poisoning or death.
The following steps shall be followed for each appliance connected to the venting system being
placed into operation, while all other appliances
connected to the venting system are not in
operation:

6 − After determining that each appliance connected to the
common venting system is venting properly, (step 3)
return all doors, widows, exhaust fans, fireplace dampers, and any other gas−burning appliances to their previous mode of operation.

1 − Seal any unused openings in the common venting system.

7 − If a venting problem is found during any of the preceding tests, the common venting system must be modified to correct the problem.

2 − Inspect the venting system for proper size and horizontal
pitch. Determine that there is no blockage, restriction,
leakage, corrosion, or other deficiencies which could
cause an unsafe condition.

Resize the common venting system to the minimum
vent pipe size determined by using the appropriate
tables in Appendix G. (These are in the current standards of the National Fuel Gas Code ANSI Z223.1.

Page 22

Gas Piping

CAUTION
If a flexible gas connector is required or allowed by
the authority that has jurisdiction, black iron pipe
shall be installed at the gas valve and extend outside
the furnace cabinet. The flexible connector can then
be added between the black iron pipe and the gas
supply line.
Gas Supply
1 − This unit is shipped standard for left or right side installation of gas piping (or top entry in horizontal applications). Connect the gas supply to the piping assembly.
2 − When connecting the gas supply piping, consider factors such as length of run, number of fittings, and furnace rating to avoid excessive pressure drop. Table 9
lists recommended pipe sizes for typical applications.
3 − The gas piping must not run in or through air ducts,
clothes chutes, gas vents or chimneys, dumb waiters,
or elevator shafts.

4 − The piping should be sloped 1/4 inch (6.4 mm) per 15
feet (4.57 m) upward toward the meter from the furnace. The piping must be supported at proper intervals
[every 8 to 10 feet (2.44 to 3.01 m)] with suitable hangers or straps. Install a drip leg in vertical pipe runs to the
unit.
5 − A 1/8" N.P.T. plugged tap or pressure post is located
on the gas valve to facilitate test gauge connection.
See figures 35 and 36.
6 − In some localities, codes may require the installation of
a manual main shut-off valve and union (furnished by
the installer) external to the unit. The union must be of
the ground joint type.

IMPORTANT
Compounds used on threaded joints of gas piping
must be resistant to the actions of liquified petroleum gases.
NOTE − If emergency shutoff is necessary, shut off the main
manual gas valve and disconnect main power to the furnace. The installer should properly label these devices.

TABLE 9
Gas Pipe Capacity − ft3/hr (m3/hr)
Nominal
Iron Pipe
Size
inches
(mm)

Internal
Diameter
inches
(mm)

10
(3.048)

20
(6.096)

30
(9.144)

40
(12.192)

50
(15.240)

60
(18.288)

70
(21.336)

80
(24.384)

90
(27.432)

100
(30.480)

1/2
(12.7)

.622
(17.799)

175
(4.96)

120
(3.40)

97
(2.75)

82
(2.32)

73
(2.07)

66
(1.87)

61
(1.73)

57
(1.61)

53
(1.50)

50
(1.42)

3/4
(19.05)

.824
(20.930)

360
(10.19)

250
(7.08)

200
(5.66)

170
(4.81)

151
(4.28)

138
(3.91)

125
(3.54)

118
(3.34)

110
(3.11)

103
(2.92)

1
(25.4)

1.049
(26.645)

680
(919.25)

465
(13.17)

375
(10.62)

320
(9.06)

285
(8.07)

260
(7.36)

240
(6.80)

220
(6.23)

205
(5.80)

195
(5.52)

1−1/4
(31.75)

1.380
(35.052)

1400
(39.64)

950
(26.90)

770
(21.80)

660
(18.69)

580
(16.42)

530
(15.01)

490
(13.87)

460
(13.03)

430
(12.18)

400
(11.33)

1−1/2
(38.1)

1.610
(40.894)

2100
(59.46)

460
(41.34)

1180
(33.41)

990
(28.03)

900
(25.48)

810
(22.94)

750
(21.24)

690
(19.54)

650
(18.41)

620
(17.56)

2
(50.8)

2.067
(52.502)

3950
(111.85)

2750
(77.87)

2200
(62.30)

1900
(53.80)

1680
(47.57)

1520
(43.04)

1400
(39.64)

1300
(36.81)

1220
(34.55)

1150
(32.56)

2−1/2
(63.5)

2.469
(67.713)

6300
(178.39)

4350
(123.17)

3520
(99.67)

3000
(84.95

2650
(75.04)

2400
(67.96)

2250
(63.71)

2050
(58.05)

1950
(55.22)

1850
(52.38)

3
(76.2)

3.068
(77.927)

11000
(311.48)

7700
(218.03)

6250
(176.98)

5300
(150.07)

4750
(134.50)

4300
(121.76)

3900
(110.43)

3700
(104.77)

3450
(97.69)

3250
(92.03)

Length of Pipe − feet (m)

NOTE − Capacity given in cubic feet (m 3 ) of gas per hour and based on 0.60 specific gravity gas.

Page 23

Left Side Piping
(Standard)
MANUAL
MAIN SHUT−OFF
VALVE
(With 1/8 in. NPT
Plugged Tap Shown)

MANUAL
MAIN SHUT−OFF
VALVE
(With 1/8 in. NPT
Plugged Tap
Shown)
GROUND
JOINT
UNION

AUTOMATIC
GAS VALVE
AUTOMATIC
GAS VALVE

GROUND
JOINT
UNION

DRIP LEG

Right Side Piping
(Alternate)

FIELD
PROVIDED
AND INSTALLED

DRIP LEG

NOTE − BLACK IRON PIPE ONLY TO BE ROUTED INSIDE OF CABINET

FIGURE 25
Horizontal Applications
Possible Gas Piping Configurations
MANUAL
MAIN SHUT−OFF
VALVE
MANUAL
MAIN SHUT−OFF
VALVE

Horizontal Application
Left−Side Air Discharge

GROUND
JOINT
UNION

DRIP LEG

MANUAL
MAIN SHUT−OFF
VALVE

FIELD
PROVIDED
AND
INSTALLED

Horizontal Application
Right−Side Air Discharge

GROUND
JOINT
UNION

NOTE − BLACK IRON PIPE ONLY TO BE ROUTED INSIDE OF CABINET

DRIP LEG

FIGURE 26
supply system the during any pressure testing of the gas
supply system at pressures less than or equal to 1/2 psig
After gas piping is completed, carefully check all piping
(3.48 kPa, 14 inches w.c.).
connections (factory− and field−installed) for gas leaks. Use
Leak Check

a leak detecting solution or other preferred means.
NOTE − If emergency shutoff is necessary, shut off the main
manual gas valve and disconnect the main power to the
furnace. The installer should properly label these devices.

CAUTION

IMPORTANT
When testing pressure of gas lines, gas valve must
be disconnected and isolated. See figure 27. Gas
valves can be damaged if subjected to pressures
greater than 1/2 psig (3.48 kPa, 14 inches w.c.).

Some soaps used for leak detection are corrosive to
certain metals. Carefully rinse piping thoroughly after leak test has been completed. Do not use
matches, candles, flame or other sources of ignition
to check for gas leaks.
The furnace must be isolated by closing its individual
manual shut-off valve and disconnecting from from the gas

Page 24

MANUAL MAIN
SHUT−OFF VALVE
WILL NOT HOLD
NORMAL TEST
PRESSURE
1/8 NPT PLUG

ISOLATE
GAS VALVE
FURNACE

CAP

FIGURE 27

Refer to figure 33 for unit field wiring. See figures 30 and 31
for icomfort Touch® thermostat wiring in communicating
applications. Table 11 shows DIP switch and on−board link
settings for non−communicating thermostat applications.
Typical wiring schematic is shown in figure 32.

Electrical
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures

CAUTION
Electrostatic discharge can affect electronic components. Take precautions to
neutralize electrostatic charge by
touching your hand and tools to metal
prior to handling the control.
The unit is equipped with a field make−up box on the left
hand side of the cabinet. The make−up box may be moved
to the right side of the furnace to facilitate installation. If the
make−up box is moved to the right side, clip the wire ties
that bundle the wires together. The excess wire must be
pulled into the blower compartment. Secure the excess
wire to the existing harness to protect it from damage.

1 − The power supply wiring must meet Class I restrictions. Protected by either a fuse or circuit breaker, select circuit protection and wire size according to unit
nameplate.
NOTE − Unit nameplate states maximum current draw.
Maximum over−current protection allowed is shown in table
10.
TABLE 10

INTERIOR MAKE−UP BOX INSTALLATION

SL280UH Model

Maximum Over−Current
Protection (Amps)

070V36A, 09036B

090V48B, 090V60C, 110V60C,
135V60D

Left side

2 − Holes are on both sides of the furnace cabinet to facilitate wiring.
BOX

3 − Install a separate (properly sized) disconnect switch
near the furnace so that power can be turned off for
servicing.
4 − Before connecting the thermostat or the power wiring,
check to make sure the wires will be long enough for
servicing at a later date. Remove the blower access
panel to check the length of the wire.

FIGURE 28
INTERIOR MAKE−UP BOX INSTALLATION
Right Side

BOX

FIGURE 29

5 − Complete the wiring connections to the equipment.
Use the provided unit wiring diagram and the field wiring diagrams shown in table 11 and figure 33. Use
18−gauge wire or larger that is suitable for Class II rating for thermostat connections.
6 − Electrically ground the unit according to local codes or,
in the absence of local codes, according to the current
National Electric Code (ANSI/NFPA No. 70). A green
ground wire is provided in the field make−up box.
NOTE − The SL280UHV furnace contains electronic
components that are polarity sensitive. Make sure
that the furnace is wired correctly and is properly
grounded.
7 − One line voltage ACC" 1/4" spade terminal is provided
on the furnace integrated control. Any electronic air
cleaner or other accessory rated up to one amp can be
connected to this terminal with the neutral leg of the circuit being connected to the one of the provided neutral
terminals. See figure 34 for control configuration. This
terminal is energized when the indoor blower is operating.

Page 25

8 − An unpowered, normally open (dry) set of contacts with
a 1/4" spade terminal HUM" are provided for humidifier connections and may be connected to 24V or 120V.
Any humidifier rated up to one amp can be connected
to these terminals. In 120V humidifier applications the
neutral leg of the circuit can be connected to one of the
provided neutral terminals. This terminal is energized
in the heating mode.
9 − Install the room thermostat according to the instructions provided with the thermostat. See table 11 for
field wiring connections in varying applications. If the
furnace is being matched with a heat pump, refer to the
instruction packaged with the dual fuel thermostat.
Thermostat Selection

CAUTION
Field wiring for both communicating and non−communicating applications is illustrated in diagrams,
which begin on Page 27.

Indoor Blower Speeds
Non−Communicating

1 − When the thermostat is set to FAN ON," the indoor
blower will run continuously at a field selectable percentage of the second−stage cooling speed when there
is no cooling or heating demand. The factory default
setting is 38% of cool speed.
2 − When the SL280UHV is running in the heating mode,
the indoor blower will run on the heating speed designated by the positions of DIP switches 11, 12 and 13.
First stage heating will run at 91% heat speed.
3 − When there is a cooling demand, the indoor blower will
run on the cooling speed designated by the positions
of DIP switches 5 and 6. First stage cooling will run at
70% cool speed.
Communicating

NOTE − When the SL280UHV is used with icomfort
Touch® thermostat, proper indoor blower speed selections are made by the communicating thermostat.

Non−Communicating

In non−communicating applications the SL280UHV is designed to operate in a SINGLE−STAGE mode or TWO−
STAGE mode using a conventional thermostat.
For optimal performance in non−communicating applications, Lennox recommends use of a ComfortSense® 7000
high quality electronic digital thermostat or any other with
adjustable settings for 1st stage / 2nd stage on / off differentials and adjustable stage timers.
Lennox recommends the following two−stage thermostat
settings:
First heat stage differential set to 1/2 to 1 degree F; second
heat stage differential set to 1/2 or 1 degree F; second heat
stage upstage timer disabled, or set to maximum (1 hr minimum).
Communicating

In communicating applications the icomfort Touch® thermostat must be used. Refer to the instructions provided
with the thermostat for installation, set−up and operation. In
communicating system all unused thermostat wire in the
wire bundle needs to be terminated inside and out. The extra wires can terminate on the ’C" terminal of the icomfort
communication terminal strip. (RSBus). Using an additional wire come off "C" terminal and wire nut all the extra wires
together. Termination on the outdoor control must match
the indoor control.

1 − When the thermostat is set to FAN ON," the indoor
blower will run at setting determined during system
configuration.
2 − When there is a heating demand the fan will run on
heating speeds for firing rate.
3 − When there is a cooling demand, the fan will run on the
first stage and second stage cooling speed set using
the icomfort Touch® thermostat in the installer setup
mode. The factory default is based upon 400 CFM a
ton.
Generator Use − Voltage Requirements
The following requirements must be kept in mind when
specifying a generator for use with this equipment:

Page 26

The furnace requires 120 volts (Range: 102 volts to
132 volts)
The furnace operates at 60 Hz + 5% (Range: 57 Hz to
63 Hz)
The furnace integrated control requires both correct
polarity and proper ground. Both polarity and proper
grounding should be checked before attempting to operate the furnace on either permanent or temporary
power
Generator should have a wave form distortion of less
than 5% THD (total harmonic distortion)

icomfort Touch® Thermostat with SL280UHV
and Non−Communicating Outdoor Unit

icomfort Touch® Thermostat with SL280UHV
and icomfort−ENABLED Outdoor Unit

icomfort Touch® Thermostat
icomfort−Enabled SL280UHV Indoor Furnace
Non−Communicating Outdoor Air Conditioner

OPTIONAL
DISCHARGE
AIR SENSOR

icomfort Touch®
THERMOSTAT

icomfort Touch® Thermostat
icomfort−Enabled SL280UHV Indoor Furnace
icomfort−Enabled Outdoor Air Conditioner or Heat Pump

icomfort−
ENABLED
SL280UHV
FURNACE

icomfort−
ENABLED
SL280UHV
FURNACE
OPTIONAL
DISCHARGE
AIR SENSOR
OPTIONAL
OUTDOOR
AIR SENSOR

OPTIONAL
OUTDOOR
AIR SENSOR
icomfort Touch®
THERMOSTAT

icomfort− ENABLED
OUTDOOR AIR CONDITIONING
OR HEAT PUMP UNIT
NON−COMMUNICATING
OUTDOOR AIR
CONDITIONING UNIT −
1 OR 2 STAGE

CLIP ON−BOARD LINK
W915 (Y1 TO Y2) FOR
TWO−STAGE OPERATION

NOTE − On communicating systems, extra wires must terminate on the "C" icomfort terminal strip (RSBus). Use an additional wire
and come off "C" terminal and wire nut all the extra wires together. Termination on the outdoor control must match the indoor control.

icomfort Integrated Control
Outdoor Unit

icomfort Touch®

FIGURE 30

Page 27

Optional Accessories for use with any icomfort Touch® System
NOTE: icomfort Touch® THERMOSTAT SENSES HUMIDITY
& CONTROLS HUM CONTACTS TO CYCLE HUMIDIFIER
BASED ON DEMAND. NO OTHER CONTROL OR HUMIDISTAT REQUIRED.

120V CONNECTIONS
HUM" CONTACT IS
CLOSED ANYTIME
HUMIDITY DEMAND
IS PRESENT

OPTIONAL OUTDOOR AIR SENSOR FOR USE WITH HUMIDIFIER (IF NOT ALREADY IN THE SYSTEM FOR OTHER
FUNCTIONS. BUILT INTO ALL icomfort by Lennox OUTDOOR UNITS).

icomfort ENABLED
SL280UHV FURNACE

24V HUMIDIFIER CONNECTIONS

Discharge Air
Sensor (Required
for even heat)

CS 7000
THERMOSTAT

icomfort Touch®
THERMOSTAT
CONVENTIONAL
NON−COMMUNICATING SYSTEM

RSBus

COMMUNICATING SYSTEM

Maximum total
length of all connections on the
RSBus is limited
to 1500ft.
Wire gauge of
RSBus wire is 18.

*24V IN jumper not used in non−
communicating configuration
*24V IN
JUMPER

icomfort ENABLED
SL280UHV FURNACE

NOTE: 24V UV LIGHT
APPLICATIONS

icomfort
ENABLED OUTDOOR
AIR CONDITIONING OR
HEAT PUMP UNIT

icomfort Touch®
THERMOSTAT

DEHUMIDIFIER
CONTROL

(POWER COMPANY INTERRUPTION SYSTEMS
ARE WIRED SAME AS OVERFLOW SWITCH)

HVAC EQUIP
Rf Cf Gs Gh W DH

icomfort ENABLED
SL280UHV FURNACE

In an icomfort by Lennox system,
neither furnace nor air handler transformer will have adequate VA to
power 24V UV light applications. An
additional transformer for UV light
applications is required.

HVAC
EQUIPMENT

icomfort ENABLED
SL280UHV FURNACE

HEPA BYPASS FILTER X2680 HEPA INTERLOCK KIT
STANDARD 1 OR 2
STAGE AC OR HP UNIT

PASS INDOOR BLOWER
MOTOR COMMON WIRE
THROUGH CURRENT LOOP.

NON−COMMUNICATING
SYSTEM WIRING

SEE HEPA INTERLOCK KIT
FOR INSTALLATION DETAILS

icomfort ENABLED
SL280UHV FURNACE

LVCS VENTILATION CONTROL SYSTEM
SEE LVCS VENTILATION
INSTRUCTIONS FOR
DAMPER & SENSOR WIRING

2 STAGE FURNACE
DS

CUT
R−DS
W914

FIGURE 31
Page 28

COMMUNICATING
SYSTEM WIRING
R

TABLE 11
SL280 Field Wiring Applications With Conventional Thermostat
DIP Switch Settings and On−Board Links (See figure 34)

Thermostat

DIP Switch 1
Thermostat
Heating
Stages

1 Heat / 1 Cool
NOTE − Use DIP
switch 2 to set
second−stage
heat ON delay.
OFF−7 minutes.
ON−12 minutes.

1 Heat / 2 Cool
NOTE − Use DIP
switch 2 to set
second−stage
heat ON delay.
OFF−7 minutes.
ON−12 minutes.

1 Heat / 2 Cool
with t’stat with
humidity control
NOTE − Use DIP
switch 2 to set
second−stage
heat ON delay.
OFF−7 minutes.
ON−12 minutes.

On Board Links Must Be Cut To Select
System Options

Wiring Connections

S1
T’STAT

FURNACE
TERM. STRIP

OUTDOOR
UNIT

DO NOT CUT ANY
ON−BOARD LINKS

S1
T’STAT

CUT ON−BOARD LINK
W915
2 STAGE
COMPR

FURNACE
TERM. STRIP

OUTDOOR
UNIT

S1
T’STAT

CUT ON−BOARD LINK
W915
2 STAGE
COMPR

FURNACE
OUTDOOR
TERM. STRIP
UNIT

*
CUT ON−BOARD LINK
W914
DEHUM
OR
HARMONY

o
* Not required on all units.

Page 29

TABLE 11
SL280 Field Wiring Applications With Conventional Thermostat (Continued)
DIP Switch Settings and On−Board Links (See figure 34)

Thermostat

DIP Switch 1
Thermostat
Heating
Stages

2 Heat / 2 Cool

On Board Links Must Be Cut To Select
System Options

OFF

Wiring Connections

S1
T’STAT

CUT ON−BOARD LINK
W915
2 STAGE
COMPR

FURNACE
TERM. STRIP

OUTDOOR
UNIT

2 Heat / 2 Cool
with t’stat with
humidity control

OFF

S1
T’STAT

CUT ON−BOARD LINK
W915
2 STAGE
COMPR

FURNACE
OUTDOOR
TERM. STRIP
UNIT

*
CUT ON−BOARD LINK
W914
DEHUM
OR
HARMONY

o
2 Heat / 1 Cool
with t’stat with
humidity control

OFF

S1
T’STAT

FURNACE
OUTDOOR
TERM. STRIP
UNIT

CUT ON−BOARD LINK
W914
DEHUM
OR
HARMONY

o
2 Heat / 1 Cool

OFF

S1
T’STAT

DO NOT CUT ANY
ON−BOARD LINKS

* Not required on all units.

Page 30

FURNACE
TERM. STRIP

OUTDOOR
UNIT

TABLE 11
SL280 Field Wiring Applications With Conventional Thermostat (Continued)

Thermostat

Dual Fuel
Single Stage
Heat Pump

DIP Switch Settings and On−Board Links (figure 34)
DIP Switch 1
On Board Links Must Be Cut To Select
Thermostat
System Options
Heating
Stages
L7724U
T’STAT

OFF
CUT ON−BOARD LINK
W951
HEAT
PUMP

ComfortSense
7000 L7724U
thermostat w/
dual fuel capabilities
Capable of 2
stage gas heat
control

Wiring Connections

FURNACE
TERM. STRIP

HEAT PUMP

67M41*

Y
Y2
D
B

outdoor
sensor

Dual Fuel
Two Stage
Heat Pump
ComfortSense
7000 L7724U
thermostat w/
dual fuel capabilities
Capable of 2
stage gas heat
control

OFF

L7724U
T’STAT

FURNACE
TERM. STRIP

HEAT PUMP

CUT ON−BOARD LINK
W915
2 STAGE
COMPR

CUT ON−BOARD LINK
W951
HEAT
PUMP

67M41*

D
B
T
T

out blue

outdoor
sensor

* Connect W1 to W1 ONLY if using defrost tempering kit 67M41
NOTE − Do NOT make a wire connection between the room thermostat L terminal and the L terminal of the SL280
integrated control.

Page 31

TABLE 11
SL280 Field Wiring Applications With Conventional Thermostat (Continued)

Thermostat

Dual Fuel
Single Stage
Heat Pump

DIP Switch Settings and On−Board Links (figure 34)
DIP Switch 1
On Board Links Must Be Cut To Select
Thermostat
System Options
Heating
Stages
L7724U
T’STAT

OFF

ComfortSense
7000 L7724U
thermostat w/
dual fuel capabilities
Capable of 2
stage gas heat
control w/dehumidification
control

Wiring Connections

CUT ON−BOARD LINK
W951
HEAT
PUMP

CUT ON−BOARD LINK
W914
DEHUM
OR
HARMONY

FURNACE
TERM. STRIP

HEAT PUMP

67M41*

L
Y

Y2
D
B

outdoor
sensor

Dual Fuel
Two Stage
Heat Pump
ComfortSense
7000 L7724U
thermostat w/
dual fuel capabilities
Capable of 2
stage gas heat
control w/dehumidification

OFF

CUT ON−BOARD LINK
W915
2 STAGE
COMPR

L7724U
T’STAT

FURNACE
TERM. STRIP

67M41*

CUT ON−BOARD LINK
W951
HEAT
PUMP
CUT ON−BOARD LINK
W914
DEHUM
OR
HARMONY

HEAT PUMP

D
B

T
T

out blue

outdoor
sensor

* Connect W1 to W1 ONLY if using defrost tempering kit 67M41
NOTE − Do NOT make a wire connection between the room thermostat L terminal and the L terminal of the SL280
integrated control.

Page 32

SL280UHV Schematic Wiring Diagram

FIGURE 32

Page 33

TYPICAL SL280UHV FIELD WIRING DIAGRAM

FIELD INSTALLED CLASS II 24V
FIELD INSTALLED LINE VOLTAGE

FIGURE 33

Page 34

Integrated Control
ACC
HUM
HS/ CAI

LINE 1
NEUTRAL

7 SEGMENT LED

FLAME SENSE

INDOOR
BLOWER
CONNECTOR

DIAGNOSTIC
PUSH BUTTON

DIP SWITCHES
12 PIN LOW
VOLTAGE
CONNECTOR

OUTDOOR AIR
SENSOR
TERMINALS
DISCHARGE AIR
SENSOR
TERMINALS

W915 Y1 TO Y2
2 STAGE COMPR
W951 R TO O
HEAT PUMP

TB83
COMMUNICATING
OUTDOOR
EQUIPMENT
TB84
COMMUNICATING
INDOOR
THERMOSTAT

R I+ I−C R I+ I−C

W1 W2 G Y2 Y1 C

C R DH L O DS

W914 R TO DS
DEHUM OR
HARMONY

NON−COMMUNICATINGNG
24V TERMINALS

RS−BUS LINK (TB82, future use)

THERMOSTAT CONNECTIONS (TB1)

I+ = DATA HIGH CONNECTION
I − = DATA LOW CONNECTION

DS = DEHUMIDIFICATION SIGNAL
W2 = HEAT DEMAND FROM 2ND STAGE T/STAT
W1 = HEAT DEMAND FROM 1ST STAGE T/STAT
R = CLASS 2 VOLTAGE TO THERMOSTAT
G = MANUAL FAN FROM T’STAT
C = THERMOSTAT SIGNAL GROUND CONNECTED TO
TRANSFORMER GRD (TR) & CHASIS GROUND (GRD)

RS−BUS OUTDOOR (TB83)
R = 24VAC
I + = DATA HIGH CONNECTION
I − = DATA LOW CONNECTION
C = 24VAXC COMMON

RS−BUS INDOOR (TB84)

Y1 = THERMOSTAT 1ST STAGE COOL SIGNAL

R = 24VAC
I + = DATA HIGH CONNECTION
I − = DATA LOW CONNECTION
C = 24VAXC COMMON

Y2 = THERMOSTAT 2ND STAGE COOL SIGNAL
O = THERMOSTAT SIGNAL TO HEAT PUMP
REVERSING VALVE

1/4" QUICK CONNECT TERMINALS

DH = DEHUMIDIFICATION OUTPUT COMMUNICATING
THERMOSTAT ONLY

HUM = UNPOWERED NORMALLY OPEN (DRY) CONTACTS

L = USE ONLY WITH A COMMUNICATING THERMOSTAT
AND A NON−COMMUNICATING OUTDOOR UNIT

XMFR = 120 VAC OUTPUT TO TRANSFORMER
LI = 120 VAC INPUT TO CONTROL
ACC = 120 VAC OUTPUT TO OPTIONAL ACCESSORY
NEUTRALS = 120 VAC NEUTRAL

FIGURE 34
.............

Page 35

Integrated Control DIP Switch Settings −
Conventional Thermostat (non−communicating)
SL280UHV units are equipped with a two−stage, variable
speed integrated control. This control manages ignition
timing, heating mode fan off delays and indoor blower
speeds based on selections made using the control dip
switches and jumpers. The control includes an internal
watchguard feature which automatically resets the ignition
control when it has been locked out. After one hour of continuous thermostat demand for heat, the watchguard will
break and remake thermostat demand to the furnace and
automatically reset the control to relight the furnace.
Note: All icomfort settings are set at the icomfort Touch ®
thermostat. See icomfort installation instruction. In icomfort communication system all DIP switch and clippable
link settings are ignored. For conventional thermostats proceed with DIP switch and clippable link settings as outlined
in the following.
Heating Operation DIP Switch Settings
Switch 1 −− Thermostat Selection −− This unit may be used
with either a single−stage or two−stage thermostat. The
thermostat selection is made using a DIP switch which
must be properly positioned for the particular application.
The DIP switch is factory−positioned for use with a two−
stage thermostat. If a single−stage thermostat is to be used,
the DIP switch must be repositioned.
Select OFF" for two−stage heating operation controlled by a two−stage heating thermostat (factory setting);
b − Select ON" for two−stage heating operation controlled by a single−stage heating thermostat. This setting provides a timed delay before second−stage heat
is initiated.
Switch 2 −− Second Stage Delay (Used with Single−
Stage Thermostat Only) −− This switch is used to determine the second stage on delay when a single−stage thermostat is being used. The switch is factory−set in the OFF
position, which provides a 7−minute delay before second−
stage heat is initiated. If the switch is toggled to the ON
position, it will provide a 12−minute delay before second−
stage heat is initiated. This switch is only activated when
the thermostat selector jumper is positioned for SINGLE−
stage thermostat use.
Switches 3 and 4 −− Blower−Off Delay −− The blower−on
delay of 30 seconds is not adjustable. The blower−off delay
(time that the blower operates after the heating demand
has been satisfied) can be adjusted by moving switches 3
and 4 on the integrated control. The unit is shipped from the
factory with a blower−off delay of 90 seconds. The blower
off delay affects comfort and is adjustable to satisfy individual applications. Adjust the blower off delay to achieve a
supply air temperature between 90° and 110°F at the exact
moment that the blower is de−energized. Longer off delay

settings provide lower supply air temperatures; shorter settings provide higher supply air temperatures.Table 12 provides the blower off timings that will result from different
switch settings.
TABLE 12
Blower Off Delay Switch Settings
Blower Off Delay
(Seconds)
60
90 (Factory)
120
180

Switch 3

Switch 4

On
Off
Off
On

Off
Off
On
On

Indoor Blower Operation DIP Switch Settings
Switches 5 and 6 −− Cooling Mode Blower Speed −− The
unit is shipped from the factory with the dip switches positioned for high speed (4) indoor blower motor operation
during the cooling mode. Table 13 provides the cooling
mode blower speeds that will result from different switch
settings. Switches 5 and 6 set the blower cfm for second−
stage cool. The integrated control automatically ramps
down to 70% of the second−stage cfm for first−stage cfm.
Refer to tables for corresponding cfm values.
TABLE 13
Cooling Mode Blower Speeds
Speed
Low
Medium Low
Medium High
High (Factory)

Switch 5
On
Off
On
Off

Switch 6
On
On
Off
Off

Switches 7 and 8 −− Cooling Blower Speed Adjustment
−− The unit is shipped from the factory with the dip switches
positioned for NORMAL (no) adjustment. The dip switches
may be positioned to adjust the blower speed by +10% or
−10% to better suit the application. Table 14 below provides
blower speed adjustments that will result from different
switch settings. Refer to tables for corresponding cfm values.
TABLE 14
Cooling Blower Speed Adjustment
Adjustment
+10% (approx.)
Factory Default
−10% (approx.)

Switch 7
On
Off
Off

Switch 8
Off
Off
On

Switches 9 and 10 −− Cooling Mode Blower Speed
Ramping −− Blower speed ramping may be used to enhance dehumidification performance. The switches are
factory set at option A which has the greatest effect on de−
humidification performance. Table 15 provides the cooling
mode blower speed ramping options that will result from
different switch settings. The cooling mode blower speed
ramping options are detailed on the next page.
NOTE − The off portion of the selected ramp profile also applies during heat pump operation in dual fuel applications.

Page 36

TABLE 15
Cooling Mode Blower Speed Ramping
Switch 9
Switch 10
Ramping Option
A (Factory)
Off
Off
B
Off
On
C
On
Off
D
On
On

Ramping Option D
Motor runs at 100% until demand is satisfied.

Ramping Option A (Factory Selection)
Motor runs at 50% for 30 seconds.
Motor then runs at 82% for approximately 7−1/2 minutes.
If demand has not been satisfied after 7−1/2 minutes,
motor runs at 100% until demand is satisfied.
Once demand is met, motor runs at 50% for 30 seconds then ramps down to stop.

Switches 11, 12 and 13 −− Heating Mode Blower Speed −−
The switches are factory set to the OFF position which provides factory default heat speed. Refer to table 16 for
switches 11, 12 and 13 that provided the corresponding increases or decrease to both high and low heat demand.
TABLE 16
Heating Mode Blower Speeds
Switch
Switch
Switch
Heat Speed
11
12
13

7 1/2 MIN
82% CFM

OFF

100%
CFM

1/2 MIN
50% CFM

OFF

OFF
1/2 MIN
50% CFM

COMPRESSOR DEMAND

Ramping Option B
Motor runs at 82% for approximately 7−1/2 minutes. If
demand has not been satisfied after 7−1/2 minutes,
motor runs at 100% until demand is satisfied.
Once demand is met, motor ramps down to stop.

7 1/2 MIN
100% CFM
82%CFM
COMPRESSOR DEMAND

OFF

Once demand is met, motor ramps down to stop.

OFF

100% CFM

OFF

COMPRESSOR
DEMAND

Increase 24%

Increase 18%

Off

Increase 12%

Off

Increase 6%

Off

Factory Default

Off

Decrease 6%

Off

Decrease 12%

Off

Decrease18%

Off

Switches 14 and 15 −− Continuous Blower Speed −−
Table 17 provides continuous blower speed adjustments
that will result from different switch settings.
TABLE 17
Continuous Blower Speed
Continuous
Switch 14 Switch 15
Blower Speed

Ramping Option C
Motor runs at 100% until demand is satisfied.

28% of High Cool Speed

Off

Once demand is met, motor runs at 100% for 45 seconds then ramps down to stop.

38% of High Cool Speed
(Factory)

Off

70% of High Cool Speed

Off

100% of High Cool Speed

OFF

100% CFM
COMPRESSOR
DEMAND

100% CFM

OFF

45 SEC.

Page 37

On−Board Links
Note: In icomfort systems with a conventional outdoor
unit (non−communicating), the on−board clippable links
must be set to properly configure the system.

WARNING
Carefully review all configuration information provided. Failure to properly set DIP switches, jumpers
and on−board links can result in improper operation!
On−Board Link W914 Dehum or Harmony (R to DS)
On−board link W914, is a clippable connection between terminals R and DS on the integrated control. W914 must be
cut when the furnace is installed with either the Harmony
III zone control or a thermostat which features humidity
control. If the link is left intact the PMW signal from the Harmony III control will be blocked and also lead to control
damage. Refer to table 18 for operation sequence in applications including SL280UHV, a thermostat which features humidity control and a single−speed outdoor unit.
Table 19 gives the operation sequence in applications with
a two−speed outdoor unit.
On−Board Link W951 Heat Pump (R to O)
On−board link W951 is a clippable connection between terminals R and O on the integrated control. W951 must be cut
when the furnace is installed in applications which include a
heat pump unit and a thermostat which features dual fuel
use. If the link is left intact, terminal O" will remain energized eliminating the HEAT MODE in the heat pump.

On−Board Link W915 2 Stage Compr (Y1 to Y2)
On−board link W915 is a clippable connection between terminals Y1 and Y2 on the integrated control. W915 must be
cut if two−stage cooling will be used. If the Y1 to Y2 link is
not cut the outdoor unit will operate in second−stage cooling
only.
Diagnostic LED (Figure 34)
The seven−segment diagnostic LED displays operating
status, target airflow, error codes and other information.
The table beginning on Page 60 lists diagnostic LED
codes.
Diagnostic Push Button (Figure 34)
The diagnostic push button is located adjacent to the
seven−segment diagnostic LED. This button is used to enable the Error Code Recall E" mode and the Flame Signal
F" mode. Press the button and hold it to cycle through a
menu of options. Every five seconds a new menu item will
be displayed. When the button is released, the displayed
item will be selected. Once all items in the menu have been
displayed, the menu resumes from the beginning until the
button is released.
Error Code Recall Mode
Select "E" from the menu to access the most recent 10 error
codes. Select c" from the Error Code Recall menu to clear
all error codes. Button must be pressed a second time
while c" is flashing to confirm command to delete codes.
Press the button until a solid ≡" is displayed to exit the Error
Code Recall mode.
Flame Signal Mode
Select "F" from the menu to access the flame signal mode.
The integrated control will display the flame current on 7
segment LED in in micro amps (uA).
Flame signal mode is exited after the following:
Power is reset
Pressing and holding push button until 3 horizontal
lines ≡" are displayed
10 minutes of entering the flame sense mode.

Page 38

BLOWER DATA
SL280UH070V36A BLOWER PERFORMANCE (less filter)
BOTTOM RETURN AIR
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1

Heating Speed
DIP Switch
Settings

First Stage Heating Speed - cfm

Second Stage Heating Speed - cfm

+24%

1045

1145

+18%

985

1080

+12%

940

1035

+6%

880

960

Factory Default

850

925

–6%

785

875

–12%

745

815

–18%

680

745
COOLING

Cooling Speed
DIP Switch
Settings

First Stage Cooling Speed - cfm
Low

Medium-Low

Medium-High

781

819

Factory Default

695

–

645

Second Stage Cooling Speed - cfm
High

Low

Medium-Low

Medium-High

872

981

1045

1139

1219

1372

734

797

883

943

1005

1114

1260

674

720

815

847

922

991

1144

High

SINGLE SIDE RETURN AIR
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1

Heating Speed
DIP Switch
Settings

First Stage Heating Speed - cfm

Second Stage Heating Speed - cfm

+24%

1050

1165

+18%

1000

1110

+12%

940

1040

+6%

895

975

Factory Default

820

935

–6%

775

855

–12%

735

805

–18%

685

750
COOLING

Cooling Speed
DIP Switch
Settings

First Stage Cooling Speed - cfm
Low

Medium-Low

Medium-High

764

802

Factory Default

704

–

642

Second Stage Cooling Speed - cfm
High

Low

Medium-Low

Medium-High

886

977

1035

1122

1248

1360

725

793

899

949

1029

1135

1257

680

717

812

874

933

1021

1133

High

ooling and heating speeds are based on a combination of DIP switch settings on the furnace control. Refer to Installation Instructions for specific DIP Switch
C
Settings.
2
Factory default setting.
NOTES - The effect of static pressure is included in air volumes shown.
First stage HEAT is approximately 91% of the same second stage HEAT.
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan Only speed is selectable at 28%, 38%, 70% and 100% of the selected second stage cooling speed - minimum 500 cfm.
Lennox Harmony III™ Zone Control Applications - Minimum blower speed is 425 cfm.
1

Page 39

BLOWER DATA
SL280UH090V36B BLOWER PERFORMANCE (less filter)
BOTTOM RETURN AIR
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1

Heating Speed
DIP Switch
Settings

First Stage Heating Speed - cfm

Second Stage Heating Speed - cfm

+24%

1300

1420

+18%

1250

1335

+12%

1185

1285

+6%

1145

1240

Factory Default

1070

1170

–6%

1015

1100

–12%

970

1035

–18%

880

980
COOLING

Cooling Speed
DIP Switch
Settings

First Stage Cooling Speed - cfm
Low

Medium-Low

Medium-High

616

755

Factory Default

571

–

489

Second Stage Cooling Speed - cfm
High

Low

Medium-Low

Medium-High

846

980

1018

1197

1291

1399

698

767

886

909

1083

1197

1284

627

681

812

834

968

1081

1179

High

SINGLE SIDE RETURN AIR
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1

Heating Speed
DIP Switch
Settings

First Stage Heating Speed - cfm

Second Stage Heating Speed - cfm

+24%

1305

1425

+18%

1250

1350

+12%

1195

1290

+6%

1135

1230

Factory Default

1070

1165

–6%

995

1100

–12%

935

1030

–18%

870

960
COOLING

Cooling Speed
DIP Switch
Settings

First Stage Cooling Speed - cfm
Low

Medium-Low

Medium-High

611

731

Factory Default

575

–

519

Second Stage Cooling Speed - cfm
High

Low

Medium-Low

Medium-High

830

971

995

1160

1274

1376

674

748

870

889

1075

1160

1270

604

691

786

808

952

1056

1147

High

Cooling and heating speeds are based on a combination of DIP switch settings on the furnace control. Refer to Installation Instructions for specific DIP Switch
Settings.
2
Factory default setting.
NOTES - The effect of static pressure is included in air volumes shown.
First stage HEAT is approximately 91% of the same second stage HEAT.
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan Only speed is selectable at 28%, 38%, 70% and 100% of the selected second stage cooling speed - minimum 500 cfm.
Lennox Harmony III™ Zone Control Applications - Minimum blower speed is 455 cfm.
1

Page 40

BLOWER DATA
SL280UH090V48B BLOWER PERFORMANCE (less filter)
BOTTOM RETURN AIR
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1

Heating Speed
DIP Switch
Settings

First Stage Heating Speed - cfm

Second Stage Heating Speed - cfm

+24%

1280

1410

+18%

1220

1340

+12%

1155

1270

+6%

1095

1205

Factory Default

1035

1135

–6%

970

1070

–12%

910

1000

–18%

845

930
COOLING

Cooling Speed
DIP Switch
Settings

First Stage Cooling Speed - cfm
Low

Medium-Low

Medium-High

670

890

Factory Default

605

–

525

Second Stage Cooling Speed - cfm
High

Low

Medium-Low

Medium-High

1040

1210

1030

1335

1550

1755

815

965

1090

940

1205

1405

1,600

690

850

985

795

1060

1260

1435

High

SINGLE SIDE RETURN AIR
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1

Heating Speed
DIP Switch
Settings

First Stage Heating Speed - cfm

Second Stage Heating Speed - cfm

+24%

1280

1410

+18%

1220

1340

+12%

1155

1270

+6%

1095

1205

Factory Default

1035

1135

–6%

970

1070

–12%

910

1000

–18%

845

930
COOLING

Cooling Speed
DIP Switch
Settings

First Stage Cooling Speed - cfm
Low

Medium-Low

Medium-High

640

900

Factory Default

570

–

530

Second Stage Cooling Speed - cfm
High

Low

Medium-Low

Medium-High

1015

1175

1005

1295

1500

1670

780

930

1040

895

1160

1345

1500

700

810

955

795

1050

1210

1405

Page 41

High

BLOWER DATA
SL280UH090V48B BLOWER PERFORMANCE (less filter)
SIDE RETURN AIR WITH OPTIONAL RETURN AIR BASE
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1

Heating Speed
DIP Switch
Settings

First Stage Heating Speed - cfm

Second Stage Heating Speed - cfm

+24%

1295

1425

+18%

1235

1355

+12%

1170

1290

+6%

1110

1220

Factory Default

1045

1150

–6%

980

1080

–12%

920

1010

–18%

855

945
COOLING

Cooling Speed
DIP Switch
Settings

First Stage Cooling Speed - cfm
Low

Medium-Low

Medium-High

660

905

Factory Default

600

–

535

Second Stage Cooling Speed - cfm
High

Low

Medium-Low

Medium-High

1030

1175

985

1290

1495

1675

760

930

1045

905

1125

1345

1525

700

850

970

815

1040

1225

1385

Page 42

High

BLOWER DATA
SL280UH090V60C BLOWER PERFORMANCE (less filter)
BOTTOM RETURN AIR, RETURN AIR FROM BOTH SIDES OR RETURN AIR FROM BOTTOM AND ONE SIDE
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1

Heating Speed
DIP Switch
Settings

First Stage Heating Speed - cfm

Second Stage Heating Speed - cfm

+24%

1420

1565

+18%

1355

1490

+12%

1285

1415

+6%

1215

1335

Factory Default

1145

1260

–6%

1080

1185

–12%

1010

1110

–18%

940

1035
COOLING

Cooling Speed
DIP Switch
Settings

First Stage Cooling Speed - cfm
Low

Medium-Low

Medium-High

1110

1205

1420

Factory Default

1005

1100

–

890

1015

Second Stage Cooling Speed - cfm
Low

Medium-Low

Medium-High

1680

1575

1740

2000

2305

1280

1545

1440

1595

1820

2125

1125

1380

1295

1450

1610

1930

High

SINGLE SIDE RETURN AIR
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1

Heating Speed
DIP Switch
Settings

First Stage Heating Speed - cfm

Second Stage Heating Speed - cfm

+24%

1360

1500

+18%

1295

1425

+12%

1230

1355

+6%

1165

1280

Factory Default

1100

1210

–6%

1030

1135

–12%

965

1065

–18%

900

990
COOLING

Cooling Speed
DIP Switch
Settings

First Stage Cooling Speed - cfm
Low

Medium-Low

Medium-High

1050

1165

Factory Default

955

–

840

Second Stage Cooling Speed - cfm
High

Low

Medium-Low

Medium-High

1335

1620

1515

1680

1915

2225

1060

1215

1480

1390

1545

1735

2060

945

1090

1290

1220

1385

1580

1825

Page 43

High

BLOWER DATA
SL280UH090V60C BLOWER PERFORMANCE (less filter)
SIDE RETURN AIR WITH OPTIONAL RETURN AIR BASE
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1

Heating Speed
DIP Switch
Settings

First Stage Heating Speed - cfm

Second Stage Heating Speed - cfm

+24%

1360

1495

+18%

1290

1420

+12%

1225

1350

+6%

1160

1275

Factory Default

1095

1205

–6%

1030

1130

–12%

965

1060

–18%

900

990
COOLING

Cooling Speed
DIP Switch
Settings

First Stage Cooling Speed - cfm
Low

Medium-Low

Medium-High

1050

1190

Factory Default

970

–

880

Second Stage Cooling Speed - cfm
High

Low

Medium-Low

Medium-High

1380

1615

1515

1715

1930

2240

1090

1245

1485

1380

1560

1755

2070

985

1095

1285

1215

1400

1580

1830

Page 44

High

BLOWER DATA
SL280UH110V60C BLOWER PERFORMANCE (less filter)
BOTTOM RETURN AIR, RETURN AIR FROM BOTH SIDES OR RETURN AIR FROM BOTTOM AND ONE SIDE
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1

Heating Speed
DIP Switch
Settings

First Stage Heating Speed - cfm

Second Stage Heating Speed - cfm

+24%

1690

1855

+18%

1605

1765

+12%

1525

1675

+6%

1445

1585

Factory Default

1360

1495

–6%

1280

1405

–12%

1200

1315

–18%

1115

1230
COOLING

Cooling Speed
DIP Switch
Settings

First Stage Cooling Speed - cfm
Low

Medium-Low

Medium-High

1060

1220

Factory Default

970

–

875

Second Stage Cooling Speed - cfm
High

Low

Medium-Low

Medium-High

1330

1565

1535

1710

1910

2210

1075

1180

1430

1400

1565

1715

2015

980

1070

1255

1260

1400

1560

1815

High

SINGLE SIDE RETURN AIR
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1

Heating Speed
DIP Switch
Settings

First Stage Heating Speed - cfm

Second Stage Heating Speed - cfm

+24%

1640

1805

+18%

1560

1715

+12%

1480

1630

+6%

1400

1545

Factory Default

1325

1455

–6%

1245

1370

–12%

1165

1280

–18%

1085

1195
COOLING

Cooling Speed
DIP Switch
Settings

First Stage Cooling Speed - cfm
Low

Medium-Low

Medium-High

1020

1160

Factory Default

940

–

835

Second Stage Cooling Speed - cfm
High

Low

Medium-Low

Medium-High

1285

1550

1505

1690

1855

2125

1050

1155

1400

1375

1525

1685

1935

945

1020

1250

1235

1380

1505

1730

Page 45

High

BLOWER DATA
SL280UH110V60C BLOWER PERFORMANCE (less filter)
SIDE RETURN AIR WITH OPTIONAL RETURN AIR BASE
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1

Heating Speed
DIP Switch
Settings

First Stage Heating Speed - cfm

Second Stage Heating Speed - cfm

+24%

1635

1800

+18%

1555

1710

+12%

1475

1625

+6%

1395

1535

Factory Default

1320

1450

–6%

1240

1365

–12%

1160

1275

–18%

1080

1190
COOLING

Cooling Speed
DIP Switch
Settings

First Stage Cooling Speed - cfm
Low

Medium-Low

Medium-High

1085

1160

Factory Default

1010

–

900

Second Stage Cooling Speed - cfm
High

Low

Medium-Low

Medium-High

1270

1490

1595

1660

1840

2115

1040

1160

1375

1470

1535

1655

1940

955

1025

1205

1315

1365

1510

1735

High

Page 46

BLOWER DATA
SL280UH135V60D BLOWER PERFORMANCE (less filter)
BOTTOM RETURN AIR, RETURN AIR FROM BOTH SIDES OR RETURN AIR FROM BOTTOM AND ONE SIDE
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1

Heating Speed
DIP Switch
Settings

First Stage Heating Speed - cfm

Second Stage Heating Speed - cfm

+24%

1875

2065

+18%

1785

1965

+12%

1695

1865

+6%

1605

1765

Factory Default

1515

1665

–6%

1425

1565

–12%

1330

1465

–18%

1240

1365
COOLING

Cooling Speed
DIP Switch
Settings

First Stage Cooling Speed - cfm
Low

Medium-Low

Medium-High

1025

1120

Factory Default

965

–

875

Second Stage Cooling Speed - cfm
High

Low

Medium-Low

Medium-High

1325

1650

1500

1600

1840

2235

1015

1180

1490

1420

1510

1700

2110

930

1060

1350

1225

1320

1505

1840

High

SINGLE SIDE RETURN AIR
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1

Heating Speed
DIP Switch
Settings

First Stage Heating Speed - cfm

Second Stage Heating Speed - cfm

1850

2035

+24%
+18%

1760

1935

+12%

1670

1835

+6%

1580

1740

Factory Default

1490

1640

–6%

1400

1540

–12%

1310

1445

–18%

1225

1345
COOLING

Cooling Speed
DIP Switch
Settings

First Stage Cooling Speed - cfm
Low

Medium-Low

Medium-High

1030

1105

Factory Default

960

–

845

Second Stage Cooling Speed - cfm
High

Low

Medium-Low

Medium-High

1305

1635

1525

1600

1840

2255

1005

1175

1480

1355

1435

1635

2035

925

1050

1340

1240

1315

1520

1850

Page 47

High

BLOWER DATA
SL280UH135V60D BLOWER PERFORMANCE (less filter)
SIDE RETURN AIR WITH OPTIONAL RETURN AIR BASE
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1

Heating Speed
DIP Switch
Settings

First Stage Heating Speed - cfm

Second Stage Heating Speed - cfm

+24%

1840

2025

+18%

1750

1925

+12%

1660

1830

+6%

1575

1730

Factory Default

1485

1630

–6%

1395

1535

–12%

1305

1435

–18%

1215

1340
COOLING

Cooling Speed
DIP Switch
Settings

First Stage Cooling Speed - cfm
Low

Medium-Low

Medium-High

1035

1105

Factory Default

955

–

860

Second Stage Cooling Speed - cfm
High

Low

Medium-Low

Medium-High

1285

1610

1530

1610

1825

2240

1005

1145

1430

1365

1450

1650

2040

935

1050

1295

1225

1310

1515

1850

Page 48

High

TABLE 18
OPERATING SEQUENCE
SL280UHV, Non−Communicating Thermostat with Humidity Control Feature and Single−Speed Outdoor Unit
OPERATING
SEQUENCE

SYSTEM DEMAND
Thermostat Demand

System
Condition

Step

W
1

SYSTEM RESPONSE

Relative Humidity
Compressor

Blower
CFM
(COOL)

Status

Acceptable

24
VAC

High

100%

Comments

NO CALL FOR DEHUMIDIFICATION
Normal Operation

Compressor and indoor
blower follow thermostat
demand

BASIC MODE (only active on a Y1 thermostat demand)
Normal Operation

Acceptable

24
VAC

High

100%

Dehumidification
Call

Demand

0
VAC

High

70%*

ComfortSense® 7000
thermostat energizes Y1
and de−energizes D on a
call for de−humidification

PRECISION MODE (operates independent of a Y1 thermostat demand)
Normal Operation

Acceptable

24
VAC

High

100%

Dehumidification
call

Demand

0
VAC

High

70%*

Dehumidification
call ONLY

Demand

0
VAC

High

70%*

Jumpers at indoor unit with a single stage outdoor unit
With Condensing unit − Cut W914 (R to DS) on SureLight® control
With Heat Pump − Cut W914 (R to DS) & W951 (R to O) on SureLight® control

Dehumidification mode
begins when humidity is
greater than set point
ComfortSense® 7000
thermostat will try to
maintain room humidity
setpoint by allowing the
room space to maintain a
cooler room thermostat
setpoint**

Dave Lennox ComfortSense ® 7000 thermostat to use for this application − Y2081 4 heat / 2 cool
*Dehumidification blower speed is 70% of COOL speed for all units .
**In Precision mode, ComfortSense ® 7000 thermostat will maintain room temperature up to 2 °F (1.2°C) cooler than room setting.

Page 49

TABLE 19
OPERATING SEQUENCE
SL280UHV, Non−Communicating Thermostat with Humidity Control Feature and Two−Speed Outdoor Unit
OPERATING
SEQUENCE

SYSTEM DEMAND
Thermostat Demand

System
Condition

Ste
p

W
1

SYSTEM RESPONSE

Relative Humidity
W
2

Status

Compressor

Blower
CFM
(COOL)

Comments

NO CALL FOR DEHUMIDIFICATION
Normal Operation − Y1

Acceptable

24
VAC

Low

70%*

Normal Operation − Y2

On On

Acceptable

24
VAC

High

100%

Compressor and indoor
blower follow thermostat
demand

ROOM THERMOSTAT CALLS FOR FIRST STAGE COOLING
BASIC MODE (only active on a Y1 thermostat demand)
Normal Operation

Acceptable

24
VAC

Low

70%*

Dehumidification
Call

On On

Demand

0
VAC

High

70%**

ComfortSense® 7000
thermostat energizes Y2
and de−energizes D on a
call for de−humidification

PRECISION MODE (operates independent of a Y1 thermostat demand)
Normal Operation

Acceptable

24
VAC

Low

70%*

Dehumidification
call

On On

Demand

0
VAC

High

70%**

Dehumidification
call ONLY

On On

Demand

0
VAC

High

70%**

ROOM THERMOSTAT CALLS FOR FIRST AND SECOND STAGE COOLING
BASIC MODE (only active on a Y1 thermostat demand)
Normal Operation

On On

Acceptable

24
VAC

High

100%

Dehumidification
Call

On On

Demand

0
VAC

High

70%**

ComfortSense® 7000
thermostat energizes Y2
and de−energizes D on a
call for de−humidification

PRECISION MODE (operates independent of a Y1 thermostat demand)
Normal Operation

Acceptable

24
VAC

Low

70%*

Dehumidification
call

On On

Demand

0
VAC

High

70%**

Dehumidification
call ONLY

On On

Demand

0
VAC

High

70%**

Jumpers at indoor unit with a two stage outdoor unit
Cut factory jumper from Y1 to Y2 or cut W915 (Y1 to Y2)
With Condensing unit − Cut W914 (R to DS) on SureLight® control
With Heat Pump − Cut W914 (R to DS) & W951 (R to O) on SureLight® control

Dave Lennox ComfortSense ® 7000 thermostat to use for this application − Y2081 4 heat / 2 cool
*Normal operation first stage cooling blower speed is 70% COOL speed.
**Dehumidification blower speed is, reduced to 70% of COOL.
***In Precision mode, ComfortSense ® 7000 thermostat will maintain room temperature up to 2 °F (1.2°C) cooler than room setting.

Page 50

2 − Set the thermostat to the lowest setting.

Unit Start−Up
FOR YOUR SAFETY READ BEFORE LIGHTING

WARNING
Do not use this furnace if any part has been underwater. Immediately call a licensed professional service
technician (or equivalent) to inspect the furnace and
to replace any part of the control system and any gas
control which has been under water.

WARNING

3 − Turn off all electrical power to the unit.
4 − This furnace is equipped with an ignition device which
automatically lights the burners. Do not try to light the
burners by hand.
5 − Remove the upper access panel.
6 − Move gas valve switch to OFF position. Do not force.
See figure 35 or 36.
7 − Wait five minutes to clear out any gas. If you then smell
gas, STOP! Immediately call your gas supplier from a
neighbor’s phone. Follow the gas supplier’s instructions. If you do not smell gas go to next step.
WHITE RODGERS GAS VALVE

If overheating occurs or if gas supply fails to shut off,
shut off the manual gas valve to the appliance before
shutting off electrical supply.

INLET PRESSURE POST

MANIFOLD
PRESSURE TAP

HIGH FIRE ADJUSTMENT
SCREW
(under cap)

CAUTION
Before attempting to perform any service or maintenance, turn the electrical power to unit OFF at disconnect switch.

WARNING
During blower operation, the ECM motor emits energy that may interfere with pacemaker operation. Interference is reduced by both the sheet metal cabinet
and distance.
BEFORE LIGHTING smell all around the appliance area for
gas. Be sure to smell next to the floor because some gas is
heavier than air and will settle on the floor.

GAS VALVE SHOWN IN ON POSITION

FIGURE 35
HONEYWELL GAS VALVE
INLET PRESSURE TAP
ON SIDE

HIGH FIRE
ADJUSTING SCREW
(under cap)

The gas valve on the SL280UHV unit will be equipped with
a gas control switch. Use only your hand to move the
switch. Never use tools. If the switch will not turn or if the
control switch will not move by hand, do not try to repair it.
Placing the furnace into operation:
SL280UHV units are equipped with an automatic ignition
system. Do not attempt to manually light burners on these
furnaces. Each time the thermostat calls for heat, the
burners will automatically light. The ignitor does not get
hot when there is no call for heat on units with an automatic
ignition system.

GAS VALVE SHOWN IN ON POSITION

MANIFOLD
PRESSURE
TAP ON
SIDE

FIGURE 36

WARNING
If you do not follow these instructions exactly, a fire
or explosion may result causing property damage,
personal injury or death.

8 − Move gas valve switch to ON position. Do not force.
See figure 35 or 36.
9 − Replace the upper access panel.
10− Turn on all electrical power to to the unit.

Gas Valve Operation (Figures 35 and 36)

11− Set the thermostat to desired setting.

1 − STOP! Read the safety information at the beginning of
this section.

NOTE − When unit is initially started, steps 1 through 11
may need to be repeated to purge air from gas line.

Page 51

TABLE 20
GAS METER CLOCKING CHART
Seconds for One Revolution
Natural
LP
SL280
Unit
1 cu ft
2 cu ft
1 cu ft
2 cu ft
Dial
Dial
Dial
DIAL
−045
80
160
200
400
−70
55
110
136
272
−90
41
82
102
204
−110
33
66
82
164
−135
27
54
68
136

12− If the appliance will not operate, follow the instructions
Turning Off Gas to Unit" and call your service technician or gas supplier.
Turning Off Gas to Unit
1 − Set the thermostat to the lowest setting.
2 − Turn off all electrical power to the unit if service is to be
performed.
3 − Remove the upper access panel.
4 − Move gas valve switch to OFF position. Do not force.
See figure 35 or 36.
5 − Replace the upper access panel.
Failure To Operate
If the unit fails to operate, check the following:
1 − Is the thermostat calling for heat?
2 − Are access panels securely in place?
3 − Is the main disconnect switch closed?
4 − Is there a blown fuse or tripped circuit breaker?
5 − Is the filter dirty or plugged? Dirty or plugged filters will
cause the limit control to shut the unit off.
6 − Is gas turned on at the meter?
7 − Is the manual main shut-off valve open?
8 − Is the internal manual shut-off valve open?
9 − Is the unit ignition system in lock out? If the unit locks out
again, call the service technician to inspect the unit for
blockages.
10 −Is pressure switch closed? Obstructed flue will cause
unit to shut off at pressure switch. Check flue and outlet
for blockages.
11 −Are flame rollout switches tripped? If flame rollout
switches are tripped, call the service technician for inspection.

Gas Pressure Adjustment
Furnace should operate at least 5 minutes before checking gas flow. Determine time in seconds for two revolutions of gas through the meter. (Two revolutions assures a
more accurate time.) Divide by two and compare to time
in table 20 below. If manifold pressure matches table 22
and rate is incorrect, check gas orifices for proper size and
restriction. Remove temporary gas meter if installed.
NOTE − Shut unit off and remove manometer as soon as an
accurate reading has been obtained. Take care to replace
pressure tap plug.

Natural−1000 btu/cu ft

LP−2500 btu/cu ft

Supply Line Pressure
White Rodgers Gas Valve

An inlet post located on the gas valve provides access to
the supply pressure. See figure 35. Back out the 3/32 hex
screw one turn, connect a piece of 5/16 tubing and connect
to a manometer to measure supply pressure. See table 22
for supply line pressure.
Honeywell Gas Valve

A threaded plug on the inlet side of the gas valve provides
access to the supply pressure tap. Remove the threaded
plug, install a field−provided barbed fitting and connect a
manometer to measure supply pressure. See table 22 for
supply line pressure. Replace the threaded plug after measurements have been taken.
Manifold Pressure
NOTE − Pressure test adapter kit (10L34) is available from
Lennox to facilitate manifold pressure measurement.
1 − Connect test gauge to manifold pressure post (figure
35) or tap (figure 36) on gas valve.
2 − Ignite unit on high fire and let run for 5 minutes to allow
for steady state conditions.
3 − After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in table
22.
4 − If necessary, make adjustments. Figures 35 and 36
show location of high fire adjustment screw.
5 − If an adjustment is made on high fire, re−check manifold pressure on low fire. Do not adjust low fire manifold pressure. If low fire manifold pressure is more
than 1/2" above or below value specified in table 22,
replace valve.

Proper Combustion
Furnace should operate minimum 15 minutes with correct
manifold pressure and gas flow rate before checking combustion. Table 21 shows acceptable combustion for ALL
SL280UHV models. The maximum carbon monoxide reading should not exceed 50 ppm.
TABLE 21
Firing Rate
CO2% For Nat CO2% For L.P.

Page 52

High Fire

6.8 − 7.4

7.5 − 9.0

Low Fire

4.2 − 5.7

5.0 − 6.0

High Altitude
The manifold pressure, gas orifice and pressure switch
may require adjustment or replacement to ensure proper
operation at higher altitudes. Tables 22 through 25 shows
manifold pressure, pressures switch and gas conversion
kits at all altitudes.

IMPORTANT
For safety, shut unit off and remove manometer as
soon as an accurate reading has been obtained.
Take care to replace pressure tap plug.

TABLE 22
Manifold Pressure Settings

Unit
Input

070
090
110
135
1 This

Orifice Size
0 − 7500 ft.

Gas

Manifold
Pressure in.wg.
0−4500 ft.

Orifice Size
7501 −
10,000 ft.1

Manifold
Pressure in.wg.
4501−7500 ft.

Manifold
Pressure in.wg.
7501 − 10,000 ft.2

Supply Line
Pressure
in. w.g.

Low
Fire

High
Fire

Low
Fire

High
Fire

Low
Fire

High
Fire

Min

Max

Natural

.063

.055

1.7

3.5

1.6

3.4

1.7

3.5

4.5

13.0

LP/propane3

.039

.037

4.9

10.0

4.9

10.0

4.9

10.0

11.0

13.0

Natural

.063

.055

1.7

3.5

1.5

3.2

1.7

3.5

4.5

13.0

LP/propane3

.039

.037

4.9

10.0

4.9

10.0

4.9

10.0

11.0

13.0

Natural

.063

.055

1.7

3.5

1.5

3.2

1.7

3.5

4.5

13.0

LP/propane3

.039

.037

4.9

10.0

4.9

10.0

4.9

10.0

11.0

13.0

Natural

.063

.055

1.7

3.5

1.6

2.8

1.7

3.5

4.5

13.0

LP/propane3

.039

.037

4.9

10.0

4.9

10.0

4.9

10.0

11.0

13.0

is the only permissible derate for these units.

2 Natural

gas high altitude orifice kit required.

A natural to L.P. propane gas changeover kit is necessary to convert this unit. Refer to the changeover kit installation instruction for the conversion
procedure.
NOTE − Units may be installed at altitudes up to 4500 ft. above sea level without modifications.

TABLE 23
High Altitude Pressure Switch Kits
Unit
Input

High Altitude
Pressure Switch Kit
0 − 4500 ft.

4501 − 7500 ft.

7501 − 10,000 ft.

070

No Change

73W35

090

No Change

69W56

73W35

110

No Change

69W56

73W35

135

No Change

73W33

73W34

TABLE 24
Honeywell Gas Valve Conversion Kits

Unit
Input

High Altitude
Natural Gas
Orifice Kit

Natural Gas to
LP/ Propane Kit

TABLE 25
White Rodgers Gas Valve Conversion Kits

LP/Propane
to
Natural Gas
Kit

7501 −
10,000 ft.

0 − 7500 ft.

7501 −
10,000 ft.

0 − 7500 ft.

070

73W37

51W02

73W38

69W79

090

73W37

51W02

73W38

110

73W37

51W02

73W38

135

73W37

51W02

73W38

Unit
Input

High Altitude
Natural Gas
Orifice Kit

Natural Gas to
LP/ Propane Kit

LP/Propane
to
Natural Gas
Kit

7501 −
10,000 ft.

0 − 7500 ft.

7501 −
10,000 ft.

0 − 7500 ft.

070

77W05

77W07

77W11

77W09

69W79

090

77W05

77W07

77W11

77W09

69W79

110

77W05

77W07

77W11

77W09

69W79

135

77W05

77W07

77W11

77W09

Page 53

Other Unit Adjustments
Primary and Secondary Limits
The primary limit is located on the heating compartment
vestibule panel. The secondary limits (if equipped) are located in the blower compartment, attached to the back side
of the blower. These auto reset limits are factory set and require no adjustment.
Flame Rollout Switches (Two)
These manually reset switches are located on (or inside of)
the burner box. If tripped, check for adequate combustion
air before resetting.
Pressure Switches
The pressure switch assembly (includes two switches) is
located in the heating compartment adjacent to the combustion air inducer. These switches check for proper combustion air inducer operation before allowing ignition trial.
The switches are factory−set and require no adjustment.
Temperature Rise
Place the unit into operation with a second−stage heating
demand. After supply and return air temperatures have
stabilized, check the temperature rise. If necessary, adjust
the heating blower speed to maintain the temperature rise
within the range shown on the unit nameplate. Increase the
blower speed to decrease the temperature rise. Decrease
the blower speed to increase the temperature rise. Failure
to properly adjust the temperature rise may cause erratic
limit operation.
Thermostat Heat Anticipation
Set the heat anticipator setting (if adjustable) according to
the amp draw listed on the wiring diagram that is attached
to the unit.
NOTE − Do not secure the electrical conduit directly to the
air ducts or structure.

Heating Sequence of Operation
Electronic Ignition
The two−stage, variable speed integrated control used in
SL280UHV units has an added feature of an internal Watchguard control. The feature serves as an automatic reset device for ignition control lockout caused by ignition failure. After one hour of continuous thermostat demand for heat, the
Watchguard will break and remake thermostat demand to
the furnace and automatically reset the control to begin the
ignition sequence.
NOTE − The ignition control thermostat selection DIP switch is
factory−set in the TWO−STAGE" position.

Applications Using a Two−Stage Thermostat
See figure 37 for ignition control sequence
A − Heating Sequence −− Integrated Control Thermostat
Selection DIP Switch 1 OFF in Two−Stage" Position
(Factory Setting)
1 − On a call for heat, thermostat first−stage contacts close
sending a signal to the integrated control. The integrated control runs a self-diagnostic program and
checks high temperature limit switches for normally
closed contacts and pressure switches for normally
open contacts. The combustion air inducer is energized at low speed.
2 − Once the control receives a signal that the low pressure switch has closed, the combustion air inducer begins a 15−second pre−purge in low speed.
NOTE − If the low fire pressure switch does not close
the combustion air inducer will switch to high fire. After
a 15 second pre−purge the high fire pressure switch
will close and the unit will begin operation on high fire.
After 10 to 20 seconds of high fire operation the unit
will switch to low fire..
3 − After the pre−purge is complete, a 20−second initial ignitor warm−up period begins. The combustion air inducer continues to operate at low speed.
4 − After the 20−second warm−up period has ended, the gas
valve is energized on low fire (first stage) and ignition occurs. At the same time, the control module sends a signal to begin an indoor blower 30−second ON−delay.
When the delay ends, the indoor blower motor is energized on the low fire heating speed, the HUM contacts
close energizing the humidifier and 120V ACC terminal is energized. The furnace will continue this operation as long as the thermostat has a first−stage heating
demand.
5 − If second−stage heat is required, the thermostat second−stage heat contacts close and send a signal to the
integrated control. The integrated control initiates a
30−second second−stage recognition delay.
6 − At the end of the recognition delay, the integrated control energizes the combustion air inducer at high
speed. The control also checks the high fire (second
stage) pressure switch to make sure it is closed. The
high fire (second stage) gas valve is energized and the
indoor blower motor is energized for operation at the
high fire heating speed.
7 − When the demand for high fire (second stage) heat is
satisfied, the combustion air inducer is switched to the
low−fire heating speed and the high−fire (second
stage) gas valve is de−energized. The low−fire (first
stage) gas valve continues operation. The indoor
blower motor is switched to the low−fire heating speed.
8 − When the thermostat demand for low−fire (first stage)
heat is satisfied, the gas valve is de−energized and the
field−selected indoor blower off delay begins. The
combustion air inducer begins a 5−second post−purge
period.
9 − When the combustion air post−purge period is complete, the inducer, the HUM contacts as well as the
120V ACC terminals are de−energized. The indoor
blower is de−energized at the end of the off delay.

Page 54

4 − After the 20−second warm−up period has ended, the gas
valve is energized on low fire (first stage) and ignition occurs. At the same time, the control module sends a signal to begin an indoor blower 30−second ON−delay.
When the delay ends, the indoor blower motor is energized on the low fire heating speed and the HUM contacts are energized. The integrated control also initiates a second−stage on delay (factory−set at 7
minutes; adjustable to 12 minutes).
5 − If the heating demand continues beyond the second−
stage on delay, the integrated control energizes the
combustion air inducer at high speed. The control also
checks the high fire (second stage) pressure switch to
make sure it is closed. The high fire (second stage)
gas valve is energized and the indoor blower motor is
energized for operation at the high fire heating speed.
6 − When the thermostat heating demand is satisfied, the
combustion air inducer begins a 5−second low speed
post−purge. The field−selected indoor blower off delay
begins. The indoor blower operates at the low−fire
heating speed.
7 − When the combustion air post−purge period is complete, the inducer, the HUM contacts as well as the
120V ACC terminals are de−energized. The indoor
blower is de−energized at the end of the off delay.

Applications Using A Single−Stage Thermostat
See figure 38 for ignition control sequence
B − Heating Sequence −− Integrated Control Thermostat
Selection DIP Switch 1 ON in Single−Stage" Position
NOTE − In these applications, two−stage heat will be initiated by the integrated control if heating demand has not
been satisfied after the field adjustable period (7 or 12 minutes).
1 − On a call for heat, thermostat first−stage contacts close
sending a signal to the integrated control. The integrated control runs a self-diagnostic program and
checks high temperature limit switches for normally
closed contacts and pressure switches for normally
open contacts. The combustion air inducer is energized at low speed.
2 − Once the control receives a signal that the low pressure switch has closed, the combustion air inducer begins a 15−second pre−purge in low speed.
NOTE − If the low fire pressure switch does not close
the combustion air inducer will switch to high fire. After
a 15 second pre−purge the high fire pressure switch
will close and the unit will begin operation on high fire.
After 10 to 20 seconds of high fire operation the unit
will switch to low fire.
3 − After the pre−purge is complete, a 20−second initial ignitor warm−up period begins. The combustion air inducer continues to operate at low speed.

HEATING OPERATION WITH TWO−STAGE THERMOSTAT
1

ÉÉ

ON
OFF
1 stg heat demand
low speed CAI
ignitor
low fire gas valve
indoor blower low heat

Pre−Purge

Ignitor Warm−up

30* second
blower
Trial For
Ignition on" delay

5 SEC
Post
Purge

blower
off"
delay

30 seconds RECOGNITION PERIOD

2 stg heat demand
high speed CAI
high fire gas valve
indoor blower high heat

* Conventional thermostat 30 seconds, icomfort Touch® thermostat set for 30 adjustable 15 to 45 seconds.

FIGURE 37
HEATING OPERATION WITH SINGLE STAGE THERMOSTAT

ÉÉ

ON
OFF

Pre−Purge

Ignitor Warm−up

39
80
30* second
Trial For
blower
Ignition on" delay

5 SEC
Post
Purge

heat demand
low speed CAI
ignitor
low fire gas valve
indoor blower low heat
7 or 12 minutes after heating demand begins, furnace switches to high fire (depends on setting)
high speed CAI
high fire gas valve
indoor blower high heat
* Conventional thermostat 30 seconds, icomfort Touch® thermostat set for 30 adjustable 15 to 45 seconds.

FIGURE 38

Page 55

blower
off"
delay

Flue And Chimney
1 − Check flue pipe, chimney and all connections for tightness and to make sure there is no blockage.
2 − Check unit for proper draft.
Electrical

Service

WARNING
ELECTRICAL SHOCK, FIRE,
OR EXPLOSION HAZARD.
Failure to follow safety warnings exactly could result
in dangerous operation, serious injury, death or
property damage.
Improper servicing could result in dangerous operation, serious injury, death, or property damage.
Before servicing, disconnect all electrical power to
furnace.
When servicing controls, label all wires prior to disconnecting. Take care to reconnect wires correctly.
Verify proper operation after servicing.
At the beginning of each heating season, a qualified technician should check the system as follows:
Blower
Check the blower wheel for debris and clean if necessary.
The blower motors are prelubricated for extended bearing
life. No further lubrication is needed.

WARNING
The blower access panel must be securely in place
when the blower and burners are operating. Gas
fumes, which could contain carbon monoxide, can
be drawn into living space resulting in personal injury or death.
Filters
All SL280UHV filters are installed external to the unit. Filters should be inspected monthly. Clean or replace the filters when necessary to ensure that the furnace operates
properly. Replacement filters must be rated for high velocity airflow. Table 1 lists recommended filter sizes.

1 − Check all wiring for loose connections.
2 − Check for the correct voltage at the furnace (furnace
operating). Correct voltage is 120VAC + 10%.
3 − Check amp−draw on the blower motor with inner blower panel in place.
Unit Nameplate__________Actual__________
Cleaning the Heat Exchanger and Burners
NOTE − Use papers or protective covering in front of the furnace during cleaning.
1 − Turn off both electrical and gas power supplies to furnace.
2 − Remove flue pipe and top cap (some applications top
cap can remain) from the unit.
3 − Label the wires from gas valve, rollout switches, primary limit switch and make−up box then disconnect them.
4 − Remove the screws that secure the combustion air inducer/pressure switch assembly to the collector box.
Carefully remove the combustion air inducer to avoid
damaging blower gasket. If gasket is damaged, it must
be replaced to prevent leakage.
5 − Remove the collector box located behind the combustion air inducer. Be careful with the collector box gasket. If the gasket is damaged, it must be replaced to
prevent leakage.
6 − Disconnect gas supply piping. Remove the screw securing the burner box cover and remove cover. Remove the four screws securing the burner manifold assembly to the vestibule panel and remove the
assembly from the unit.
7 − Remove screws securing burner box and remove
burner box.
8 − NOX units only − Remove screw securing NOX insert.
Remove NOX insert. See figure 40.

Page 56

SL280UHV BURNER, COMBUSTION AIR INDUCER ASSEMBLY &
HEAT EXCHANGER REMOVAL

gasket
pressure switch
rollout switch flue transition
burner box assembly

ignitor

collector box

heat exchanger

orifice plate
sensor
combustion air inducer

gasket

burners
manifold and gas valve

retention rings

burner box cover plate

cross over

FIGURE 39
13− To clean the combustion air inducer visually inspect and
9 − Remove screws from both sides, top and bottom of
using a wire brush clean where necessary. Use comvestibule panel.
pressed air to clean off debris and any rust.
10− Remove heat exchanger. It may be necessary to
spread cabinet side to allow more room. If so, remove
14− Reinstall heat exchanger in vestibule. (Replace the
five screws from the left side or right side of cabinet.
five screws in the cabinet from step 10 if removed).
See figure 41.
15− NOX units only − replace NOX inserst.
11− Back wash using steam. Begin from the burner opening
16− Reinstall collector box and combustion air assembly.
on each clam. Steam must not exceed 275°F.
Reinstall all screws to the collector box and combustion
12− To clean burners, run a vacuum cleaner with a soft brush
attachment over the face of burners. Visually inspect inside the burners and crossovers for any blockage
caused by foreign matter. Remove any blockage. Figure
39 shows burner detail.

air inducer. Failure to replace all screws may cause
leaks. Inspect gaskets for any damage and replace if
necessary.
17− Reinstall burner box, manifold assembly and burner box
cover.

Page 57

SL280UHV NOX INSERTS

18− Reconnect all wires.
19− Reconnect top cap and vent pipe to combustion air inducer outlet.
20− Reconnect gas supply piping.
21− Turn on power and gas supply to unit.
22− Set thermostat and check for proper operation.
23− Check all piping connections, factory and field, for gas
leaks. Use a leak detecting solution or other preferred
means.

CAUTION
Some soaps used for leak detection are corrosive to
certain metals. Carefully rinse piping thoroughly after leak test has been completed. Do not use
matches, candles, flame or other sources of ignition
to check for gas leaks.
24− If a leak is detected, shut gas and electricity off and
repair leak.
25− Repeat steps 24 and 26 until no leaks are detected.

FIGURE 40
Remove 5 screws if necessary
(either side of cabinet)

26− Replace access panel.

1
2
3
4
5

FIGURE 41

Page 58

Planned Service
The following items should be checked during an annual inspection. Power to the unit must be shut off for the service technician’s safety.
Fresh air grilles and louvers (on the unit and in the room
where the furnace is installed) − Must be open and unobstructed to provide combustion air.

Operating performance − Unit must be observed during
operation to monitor proper performance of the unit and the
vent system.

Burners − Must be inspected for rust, dirt, or signs of water.

Combustion gases − Flue products must be analyzed and
compared to the unit specifications.

Vent pipe − Must be inspected for signs of water, damaged
or sagging pipe, or disconnected joints.
Unit appearance − Must be inspected for rust, dirt, signs
of water, burnt or damaged wires, or components.
Blower access panel − Must be properly in place and provide a seal between the return air and the room where the
furnace is installed.
Return air duct − Must be properly attached and provide
an air seal to the unit.

Problems detected during the inspection may make it necessary to temporarily shut down the furnace until the items
can be repaired or replaced.
Instruct the homeowners to pay attention to their
furnace. Situations can arise between annual furnace inspections that may result in unsafe operation. For instance,
items innocently stored next to the furnace may obstruct
the combustion air supply. This could cause incomplete
combustion and the production of carbon monoxide gas.

Repair Parts List
The following repair parts are available through independent Lennox dealers. When ordering parts, include the complete
furnace model number listed on the CSA International nameplate −− Example: SL280UH070V36A. All service must be
performed by a licensed professional installer (or equivalent), service agency, or gas supplier.
Heating Parts
Cabinet Parts
Upper access panel
Flame Sensor
Blower panel
Heat exchanger assembly
Top cap
Gas manifold
Control Panel Parts
Two−speed combustion air inducer
Transformer
Two−stage gas valve
Two−stage, variable speed integrated control
Main burner cluster
Door interlock switch
Main burner orifices
Circuit breaker
Pressure switch
Blower Parts
Ignitor
Blower wheel
Primary limit control
Blower housing
Flame rollout switch
Motor
Secondary limit
Motor electronics
Power choke (1 hp only)
Motor mounting frame
Motor capacitor
Blower housing cutoff plate

Page 59

Integrated Control Diagnostic Modes
Display

Action (when button released)

No change (idle)*

Remain in idle mode

Solid E"

Enter diagnostic recall mode

Solid D"

Discharge Air Installed

Solid F"

Enter flame signal mode

Solid P" (variable speed only)

Program unit capacity/size (Unit Code)**

* No change implies the display will continue to show whatever is currently being displayed for normal operation (blinking
decimal, active error code, heat state, etc..)
** After the P" is selected (by releasing the push button) the integrated control will start flashing the P" on display for 90
seconds. If push button is pressed again and held during that time, the control will start to display characters corresponding
to different variable speed furnace models for 3 seconds each. While the wanted character−model is displayed push button
has to be released. Selected option will flash display for 10 seconds and during that time push button has to be pressed
and held for 5 seconds. Once control accepts new setting it will store data in non−volatile memory and reset itself. If 10 seconds expires or push button is held less than 5 seconds, control will exit filed test mode and go in idle without programming
the unit size.

Integrated Control Diagnostic Codes
Press the diagnostic push button and hold it to cycle through a menu of options. Every five seconds a new menu item will be
displayed. Release the button when the desired mode is displayed.
When a solid "P" is displayed, the furnace capacity / size is programmed.
When the solid E" is displayed, the control enters the Diagnostic Recall (Alarm History). Diagnostic Recall mode menu
options: No change (displaying error history) remains in Diagnostic Recall mode; solid = " exits Diagnostic Recall mode;
and solid c" clears the error history. Must press button while flashing c" is displayed to clear error codes.
When the solid F" is displayed, the control enters the Flame Signal Mode. The Flame Signal Mode is exited: with power
cycle/reset, by pressing and holding the push button until 3 horizontal line are displayed = , after 10 minutes of entering
flame signal mode.
Code

Diagnostic Codes/Status of Equipment

Idle mode (Decimal blinks at 1 Hertz −− 0.5 second ON, 0.5 second OFF).
Cubic feet per minute (cfm) setting for indoor blower (1 second ON, 0.5
second OFF) / cfm setting for current mode displayed.

A
C

Cooling stage (1 second ON, 0.5 second OFF) / 1 or 2 displayed / Pause
/ cfm setting displayed / Pause / Repeat codes).

Dehumidification mode (1 second ON) / 1 second OFF) / cfm setting displayed / Pause / Repeat Codes).

Heat pump stage (1 second ON, 0.5 second OFF) / % of input rate displayed / Pause / cfm setting / Pause / Repeat codes.

Gas Heat Stage (1 second ON, 0.5 second OFF) / 1 or 2 displayed /
Pause / cfm
setting displayed / Pause / Repeat codes. Blinking during ignition.

dF
U

Defrost mode.
Discharge Air Temperature

Page 60

Action Required to Clear and Recover

Integrated Control Diagnostic Codes (continued)
Code

Diagnostic Codes/Status of Equipment

Action Required to Clear and Recover

E 105 Device communication problem − No other devices on RS BUS (Communication
system).

Equipment is unable to communicate. Indicates
numerous message errors. In most cases errors are
related to electrical noise. Make sure high voltage
power is separated from RSBus. Check for mis−
wired and/or loose connections between the stat,
indoor unit and outdoor unit. Check for a high voltage source of noise close to the system. Fault
clears after communication is restored.

E 110 Low line voltage.

Line Voltage Low (Voltage lower than nameplate
rating). Check power line voltage and correct. Alarm
clears 5 seconds after fault recovered.

E 111

Reverse line power voltage wiring. System resumes
normal operation 5 seconds after fault recovered.

Line voltage polarity reversed.

E 112 Ground not detected

System shuts down. Provide proper earth ground.
System resumes normal operation 5 seconds after
fault recovered.

E 113 High line voltage.

Line Voltage High (Voltage higher than nameplate
rating). Provide power voltage within proper range.
System resumes normal operation 5 seconds after
fault recovered.

E 114 Line voltage frequency out−of−range.

No 60 Hertz Power. Check voltage and line power
frequency. Correct voltage and frequency problems.
System resumes normal operation 5 seconds after
fault recovered.

E 115 Low 24V − Control will restart if the error recovers.

24−Volt Power Low (Range is 18 to 30 volts). Check
and correct voltage. Check for additional power−robbing equipment connected to system. May require
installation of larger VA transformer to be installed in
furnace / air handler. Clears after fault recovered.

E 116 High 24V.

24 Volt Power High (Range is 18 to 30 volts). Check
and correct voltage. Check for proper line voltage
(120V, 240V, etc.) to equipment. Clears when control senses proper voltage.

E 117 Poor ground detected (Warning only)

Provide proper grounding for unit. Check for proper
earth ground to the system. Warning only will clear
30 seconds after fault recovered.

E 120 Unresponsive device. Communication only.

Usually caused by delay in outdoor unit responding
to indoor unit poling. Recycle power. Check all wiring connections. Cleared after unresponsive device
responds to any inquiry.

E 124 Active communicating thermostat signal missing for more than 3 minutes.

Equipment lost communication with the thermostat.
Check four wiring connections, ohm wires and cycle
power at the thermostat. Alert stops all services and
waits for heartbeat message from thermostat (subnet controller). Cleared after valid thermostat (subnet controller) message is received.

E 125 Control failed self−check, internal error, failed hardware. Will restart if
error
recovers. Integrated control not communicating. Covers hardware errors
(flame sense circuit faults, pin shorts, etc.).

Hardware problem on the control. Cycle power on
control. Replace if problem prevents service and is
persistent. Critical alert. Cleared 300 seconds after
fault recovered.

E 126 Control internal communication problem.

Hardware problem on the control. Cycle power on
control. Replace if problem prevents service and is
persistent. Cleared 300 seconds after fault recovered.

Page 61

Integrated Control Diagnostic Codes (continued)
E 131 Corrupted control parameters (Verify configuration of system). Communicating only.

Reconfigure the system. Replace control if heating
or cooling is not available. Only applicable in the
communicating mode, not in startup. Exit from Commissioning and Execute ’Set Factory Default mode’.
Control will still operate on default parameter settings.

E 180 Outdoor air temperature sensor failure. Only shown if shorted or out−of−
range.

Compare outdoor sensor resistance to temperature/
resistance charts in unit installation instructions.
Replace sensor pack if necessary. At beginning of
(any) configuration, furnace or air handler control
will sense outdoor air and discharge air temperature
sensor(s). If detected (reading in range), appropriate feature will be set as ’installed’ and that could
be seen in ’About’ screen. In normal operation after
control recognizes sensors, alarm will be sent if
valid temperature reading is lost. To get rid of setting and alarm, redo configuration and make sure
that temperature sensor is marked as ’not installed’
in Indoor Unit ’About’ screen. When Indoor unit control is replaced, thermostat will ’tell’ new control if
temperature sensor is in system or not. Clears 30
seconds after fault recovered.

E 200 Hard lockout − Rollout circuit open or previously open.

Correct cause of rollout trip, or replace flame rollout
switch. Test furnace operation. Cleared after fault
recovered.

E 201 Indoor blower communication failure − Unable to communicate with blower motor.

Indoor blower communication failure (including power outage). Lost communication with indoor blower
motor. Possible causes: motor not powered, loose
wiring. Problem may be on control or motor side.
Cleared after fault recovered.

E 202 Indoor blower motor mis−match − Indoor motor horsepower does not
match unit capacity. See Page 67.

Incorrect appliance capacity code selected. Check
for proper configuring under: Unit Size Codes for
Furnace/Air Handler on configuration guide or in
installation instructions. Cleared after the correct
match is detected following a reset. (Remove thermostat from system while applying power and reprogramming.)

E 203 Appliance capacity / size is NOT programmed. Invalid unit codes refer to
configuration flow chart. See Page 67.

No appliance capacity code selected. Check for
proper configuring under: Unit Size Codes for Furnace on configuration guide or in installation instructions. Critical Alert. Cleared after valid unit code is
read following a reset. (Remove thermostat from
system while applying power and reprogramming.)

E 204 Gas valve mis−wired.

Check gas valve operation and wiring. Clears when
repaired.

E 205 Gas valve control relay contact shorted.

Check wiring on control and gas valve. If wiring is
correct, replace control.

E 206 Gas valve second−stage relay failure

Furnace will operate on 1st stage for remainder of
the heating demand. Will clear after fault recovered.
If unable to operate 2nd stage, replace control.

E 207 Hot surface ignitor sensed open − Refer to troubleshooting. See Page 68. Measure resistance of hot surface ignitor. Replace if
open or not within specified range found in IOM.
Resumes normal operation after fault is cleared.

Page 62

Integrated Control Diagnostic Codes (continued)
Code

Diagnostic Codes/Status of Equipment

Action Required to Clear and Recover

E 223

Low pressure switch failed open.

Check pressure (inches w.c.) of low pressure switch
closing on heat call. Measure operating pressure
(inches w.c.). Inspect vent and combustion air inducer for correct operation and restriction. Resumes normal operation after fault is cleared

E 224

Low pressure switch failed closed − Refer to troubleshooting. See
Page 68.

Check operation of low pressure switch to see if it is
stuck closed on heat call longer than 150 seconds.
Measure operating pressure (inches w.c.). Inspect
vent and combustion air inducer for correct operation and restriction. Resumes normal operation after
fault is cleared.

E 225

High pressure switch failed open − Refer to troubleshooting. See
Page 68.

Check pressure (inches w.c.) of high pressure
switch closing on heat call. Measure operating pressure (inches w.c.). Inspect vent and combustion air
inducer for correct operation and restriction. Resumes normal operation after fault is cleared.

E 226

High pressure switch failed closed − Refer to troubleshooting. See
Page 68.

Check operation of high pressure switch closing on
heat call. Measure operating pressure (inches w.c.).
Inspect vent and combustion air inducer for correct
operation and restriction. Resumes normal operation after fault is cleared.

E 227

Low pressure switch open during trial for ignition or run mode. Refer to
troubleshooting. See Page 68.

E 228

Combustion air inducer calibration failure

Unable to perform pressure switch calibration.
Check vent system and pressure switch wiring connections. Resumes normal operation after fault is
cleared.

E 229

Ignition on high fire

IFC switched to high fire ignition because low fire
pressure switch did not close in allowed time. No
action is needed.

E 240

Low flame current − Run mode − Refer to troubleshooting. See Page 68.

Check micro−amperes of flame sensor using control
diagnostics or field−installed mode. Clean or replace
sensor. Measure voltage of neutral to ground to ensure good unit ground. Alert clears after current
heat call has been completed.

E 241

Flame sensed out of sequence − Flame still present.

Shut off gas. Check for gas valve leak. Replace, if
necessary. Alert clears when fault is recovered.

E 250

Limit switch circuit open − Refer to troubleshooting.

Check for proper firing rate on furnace. Ensure
there is no blockage in heater. Check for proper air
flow. If limit not closed within 3 minutes, unit will go
into 1−hour soft lockout. Resumes normal operation
after fault is cleared.

E 252

Discharge air temperature too high (gas heat only).

Check temperature rise, air flow and input rate.
Cleared when heat call is finished.

E 270

Soft lockout − Exceeded maximum number of retries. No flame current
sensed.

Check for proper gas flow. Ensure that ignitor is
lighting burner. Check flame sensor current. Clears
when heat call finishes successfully.

E 271

Soft lockout − Exceeded maximum number of retries. Last retry failed due Check pressure (inches w.c.) of low pressure switch
to the pressure switch opening.
closing on heat call. Measure operating pressure
(inches w.c.). Inspect vent and combustion air inducer for correct operation and restriction. Clears
when heat call finishes successfully.

Page 63

Integrated Control Diagnostic Codes (continued)
E 272

Soft lockout − Exceeded maximum number of recycles. Last recycle due
to the pressure switch opening.

Check operation of low pressure switch to see if it is
stuck closed on heat call. Check pressure (inches
w.c.) of high pressure switch closing on heat call.
Measure operating pressure (inches w.c.). Inspect
vent and combustion air inducer for correct operation and restriction. Clears when heat call finishes
successfully.

E 273

Soft lockout − Exceeded maximum number of recycles. Last recycle due
to flame failure.

E 274

Soft lockout − Exceeded maximum number of recycles. Last recycle
failed due to the limit circuit opening or limit remained open longer than
3 minutes.

Shut down system. 1−hour soft lockout. Check firing
rate and air flow. Check for blockage. Clears when
heat call finishes successfully.

E 275

Soft lockout − Flame sensed out of sequence. Flame signal is gone.

Shut off gas. Check for gas valve leak. 1−hour soft
lockout. Clears when flame has been proven stable.

E 276

Watchguard calibration failure.

Unable to perform pressure switch calibration.
Check vent system and pressure switch wiring connections. 1−hour soft lockout. Clears when calibration has finished successfully.

E 290

Ignitor circuit fault − Failed ignitor or triggering circuitry.

Measure resistance of hot surface ignitor. Replace if
open or not within specifications. 1−hour soft lockout. Clears when flame has been proven stable.

E 291

Heat air flow restricted below the minimum.

Check for dirty filter and air flow restriction. Check
blower performance. 1−hour soft lockout. Cleared
when heat call finishes successfully.

E 292

Indoor blower motor unable to start due to obstructed wheel, seized
bearings.

Indoor blower motor unable to start (seized bearing, stuck wheel, etc.). Replace motor or wheel if
assembly does not operate or meet performance
standards. 1−hour soft lockout. Clears after circulator successfully starts.

E 294

Combustion air inducer over current.

Check combustion blower bearings, wiring and
amps. Replace if does not operate or does not meet
performance standards. Clears after inducer current
is sensed to be in−range after the ignition following
the soft lockout or reset.

E 295

Indoor blower motor temperature is too high.

Indoor blower motor over temperature (motor
tripped on internal protector). Check motor bearings
and amps. Replace if necessary. Cleared after
blower demand is satisfied.

E 310

Discharge error temperature sensor failure. Only shown if shorted or
out of range.

Compare outdoor sensor resistance to temperature/
resistance charts in installation instructions. Replace sensor if necessary. Cleared in Communicating mode: 30 seconds after fault recovered. In Non−
Communicating mode: Cleared after the current
heat call is completed.

E 311

Heat rate reduced to match indoor blower air flow.

Warning Only. Furnace blower in cutback mode due
to restricted airflow. Reduce firing rate every 60
seconds to match available CFM. Check filter and
duct system. To clear, replace filter if needed or repair/add duct. 2−stage controls will reduce firing rate
to 1st stage. Clears when heat call finishes successfully.

Page 64

Integrated Control Diagnostic Codes (continued)
Code

Diagnostic Codes/Status of Equipment

Action Required to Clear and Recover

E 312

Restricted air flow in cooling or continuous fan mode is lower than cfm
setting.

Warning Only. Restricted airflow − Indoor blower is
running at a reduced CFM (Cutback Mode − The
variable speed motor has pre−set speed and torque
limiters to protect the motor from damage caused
by operating outside of design parameters (0 to 0.8"
W.C.. total external static pressure). Check filter and
duct system. To clear, replace filter if needed or repair/add duct. Cleared after the current service demand is satisfied.

E 313

Indoor or outdoor unit capacity mismatch. Communication only.

Incorrect indoor/outdoor capacity code selected.
Check for proper configuring in installation instructions. Alarm is just a warning. The system will operate, but might not meet efficiency and capacity parameters. Alarm will clear when commissioning is
exited. Cleared after commissioning is complete.

E 331

Global network connection − Communication link problem.

For Future Use.

E 334

Relay Y1" stuck on interated control.

Replace integrated control.

E 347

No 24 Volt output on Y1 of "integrated control" with non communicating
outdoor unit.

Operation stopped. Y1 relay / Stage 1 failed. (Pilot
relay contacts did not close or the relay coil did not
energize; no input back to IFC chip). Critical Alert.
Cleared after reset and Y1 input sensed.

E 348

No 24 Volt output on Y2 of "integrated control" with non?communicating
outdoor unit.

Y2 relay / Stage 2 failed. (Pilot relay contacts did
not close or the relay coil did not energize; no input
back to IFC chip). Critical Alert. Cleared after reset
and Y1 input sensed.

E 349

No 24 Volts between R & O on "integrated control" with non communiConfiguration link R to O needs to be restored. Recating outdoor unit (Dual fuel module required for heat pump application). place link or hard−wire. Applicable in non communicating mode. Critical Alert.

E 370

Interlock switch sensed open for 2 minutes.

Control sees the loss of 24VAC for 2 minutes .Terminate all services and wait for interlock switch to
close. The alarm will clear when 24VAC is continuously sensed on DS terminal for a minimum of 10
seconds or on a power reset.

E 400

LSOM − Compressor internal overload tripped.

Thermostat demand Y1 is present; but, compressor
is not running. Check power to outdoor unit. Clears
the error after current is sensed in both RUN and
START sensors for at least 2 seconds, or after service is removed, or after power reset.

E 401

LSOM Compressor long run cycle or low system pressure.

Compressor ran more than 18 hours to satisfy a
single thermostat demand. Critical Alert. Clears the
error after 30 consecutive normal run cycles or
power reset. Also monitors low pressure switch
trips.

E 402

LSOM − Outdoor unit system pressure trip.

Discharge or suction pressure out−of−limits, or compressor overloaded. Clears the error after 4 consecutive normal compressor run cycles.

E 403

LSOM − Compressor short−cycling. .(Running less than 4 minutes). Outdoor unit pressure trip

Compressor runs less than 3 minutes to satisfy a
thermostat demand. Clears the error after 4 consecutive normal run cycles or power reset.

E 404

LSOM − Compressor rotor locked. Compressor short−cycling. (Running
less than 4 minutes).

Compressor rotor locked up due to run capacitor
short, bearings are seized, excessive liquid refrigerant, etc. Clears the error after 4 consecutive normal
run cycles or after power reset.

E 405

LSOM − Compressor open circuit.

Compressor circuit open (due to power disconnection, open fuse, etc.) Clears the error after 1 normal
compressor run cycle.

Page 65

Integrated Control Diagnostic Codes (continued)
E 406

LSOM − Compressor open start circuit.

Required amount of current is not passing through
Start current transformer. Clears the error after current is sensed in START sensor, or after power reset.

E 407

LSOM − Compressor open run circuit.

Required amount of current is not passing through
Run current transformer. Clears the error after current is sensed in RUN sensor, or 1 normal compressor run cycle, or after power reset.

E 408

LSOM − Compressor contactor is welded.

Compressor runs continuously. Clears the error
after 1 normal compressor run cycle or after power
reset.

E 409

LSOM − Compressor low voltage.

Secondary voltage is below 18VAC. After 10 minutes, operation is discontinued. Clears the code
after voltage is higher than 20 VAC for 2 seconds or
after power reset.

Page 66

Program Unit Capacity/Size Mode

−
−
−

Power−Up − Number displayed represents by integrated control unit size code (furnace model
and capacity). If three horizontal bars are displayed followed by continuous E203, furnace
control does not recognize unit size code. Configure per the following:

Furnace control in IDLE mode
No heating, cooling or indoor fan
operation)

Yes

To enter Program Unit
Capacity/Size: push
and hold button next to
7−segment LED display
until solid P" symbol
appears.
Release
button.

_
Turn room thermostat to OFF

IMPORTANT: Field replacement controls may
need to be manually configured to validate
furnace unit size code.
UNIT SIZE
CODE FURNACE MODEL

Solid P starts
blinking
on
7−Segment LED

UNIT SIZE
CODE FURNACE MODEL

SL280UH070V36A

SL280UH090V36B

SL280DF090V48B

SL280UH090V48B

SL280DF090V60C

SL280DF110V60C

SL280UH090V60C

SL280UH110V60C

SL280UH135V60D

SL280DF070V36A

When the correct unit size code is displayed, release
button. Selected code will flash for 10−second period.
During that period, press and hold push button for 5
seconds. Integrated control will store code in
memory and will automatically exit Program Unit
Capacity/Size Mode and reset. (If second period
expires or push button is held less than five seconds,
control
will
automatically
exit
Program
Capacity/Size Mode and go into IDLE mode without
storing unit size code. If this happens, programming
function must be repeated).

Push and hold button. Integrated control will
display unit size code number for each
furnace model for three seconds.

Verify that the selected unit size code is correct
and stored in non−volatile memory by cycling
the 24 volt power to the furnace control. (At 24
volt power−up of the furnace control, the
7−segment LED will display a unit size code. If
three horizontal bars display, board does not
recognize unit size code. Programming
function must be repeated)

FINISHED

Page 67

−
−
−

Troubleshooting: Heating Sequence of Operation

CALL FOR FIRST−STAGE HEAT
1

CALL FOR
1ST STAGE HEAT
(LOW FIRE)

NO
INDOOR BLOWER OFF AFTER
HEAT FAN OFF DELAY
(LOW HEAT SPEED)

HIGH
LIMIT SWITCH
CLOSED?

ERROR
CODE
FLASHES

YES
LIMIT
SWITCH
CLOSED WITHIN 3
MINUTES?

INDOOR
BLOWER
ON(LOW HEAT
SPEED)

INDOOR
BLOWER OFF
AFTER HEAT FAN
OFF DELAY (LOW
HEAT SPEED)

WATCHGUARD −
ERROR CODE
1
FLASHES
NO

YES

ROLLOUT
CIRCUITS
CLOSED?

DE−ENERGIZE
GAS VALVE

YES
LOW
PRESSURE
SWITCH
OPEN?

INDUCER ON
(HIGH SPEED)
INDOOR BLOWER
ON (LOW HEAT
SPEED)

ROLLOUT
CIRCUIT
CLOSES
(MANUAL
RE−SET)

ERROR
CODE
FLASHES

YES

NO
INDUCER OFF
AFTER POST
PURGE

ERROR CODE
FLASHES (AFTER
5 SECONDS)

INDOOR BLOWER
OFF AFTER HEAT
OFF DELAY

LOW PRESSURE
SWITCH OPENS

YES
INDUCER ON
LOW SPEED

LOW
PRESSURE SWITCH
CLOSED WITHIN 120
SECONDS?

HIGH
PRESSURE
SWITCH
OPEN
BEFORE
INDUCER WAS
TURNED ON?

CALL
FOR HEAT
ENDS?

YES

HARD LOCKOUT −
ERROR CODE
2
FLASHES

YES

INDUCER TO
HIGH SPEED−
ERROR CODE
FLASHES

LOW & HIGH
PRESSURE SWITCH
CLOSED WITHIN 30
SECONDS?

INDOOR
BLOWER
ON?

YES

YES
YES

PRE−PURGE
(15 SECONDS)

NO
INTERPURGE
(15 SECONDS)

H.S.I. ON
(20 SECONDS)
1ST STAGE GAS
VALVE ENERGIZED

YES
INDUCER OFF−
WAIT
5 MINUTES
ERROR CODE
FLASHES

INDOOR
BLOWER
OFF AFTER
HEAT FAN
OFF DELAY

3
1

NO
IGNITION TRIAL
BEGINS (H.S.I. ON)

HEAT FAN ON DELAY
TIMER STARTED

FLAME
SENSED WITHIN
4 SECONDS?

GAS VALVE
DE−ENERGIZED
H.S.I. OFF

5TH
UNSUCCESSFUL
TRIAL?

YES

POSTPURGE
(5 SECONDS)

INDUCER
OFF

WATCHGUARD −
ERROR CODE
1
FLASHES

YES
H.S.I. OFF
INDOOR
BLOWER ON 30 SEC.
(LOW HEAT SPEED)
2

WATCHGUARD LOCKOUT AUTOMATICALLY RESETS AFTER ONE HOUR

HARD LOCKOUT REQUIRES THERMOSTAT RESET OR CYCLING OF POWER TO RESET THE LOCKOUT.

IN CASE HIGH SPEED INDUCER IS RUNNING AT THE TIME THE GAS VALVE GETS ENERGIZED,
2ND STAGE GAS VALVE IS ENERGIZED INSTEAD OF 1ST STAGE. 20 SECONDS AFTER FLAME
IS SENSED, INDUCER SWITCHES TO LOW SPEED, AND GAS VALVE SWITCHES TO 1ST STAGE.

CALL FOR HEAT SATISFIED

Page 68

Troubleshooting: Heating Sequence of Operation (Continued)

CALL FOR SECOND−STAGE HEAT
2
CALL FOR 2ND STAGE HEAT
1
(HIGH FIRE)

SINGLE STAGE
THERMOSTAT 2

2 STAGE THERMOSTAT

2ND STAGE
ON DELAY
EXPIRED?

RECOGNITION DELAY
(30 SECONDS)
EXPIRED?
ONLY FOR 1ST
REQUEST FOR
2ND STAGE HEAT
YES

YES

INDUCER SWITCHED
TO HIGH SPEED

HIGH
PRESSURE SWITCH
CLOSED WITHIN 10
SECONDS?

INDUCER SWITCHED
TO LOW SPEED

5 MINUTE DELAY
(ERROR CODE FLASHES)

YES

2ND STAGE GAS VALVE
ENERGIZED

INDOOR BLOWER ENERGIZED
ON HIGH HEAT SPEED

3
CALL FOR HEAT SATISFIED

SYSTEM WILL ALWAYS LIGHT ON LOW FIIRE, EVEN IF 2ND STAGE HEAT IS IN PLACE.

WHEN USED WITH A SINGLE STAGE THERMOSTAT, SET SW1 TO THE ON POSITION IN DIP SWITCH S4.

IF THE HIGH FIRE PRESSURE SWITCH DOES NOT CLOSE WITHIN 5 ATTEMPTS, THE SYSTEM WILL OPERATE AT
LOW FIRE FOR THE REMAINDER OF THE CALL FOR HEAT REQUEST.

Page 69

Troubleshooting: Heating Sequence of Operation (Continued)

CALL FOR HEAT SATISFIED
FIRST−STAGE HEAT

SECOND−STAGE HEAT

3
RUN MODE:
1ST OR 2ND STAGE CALL FOR HEAT.
ALL INPUTS MONITORED (LIMIT, PRESSURE,
CALL FOR HEAT/COOL, FLAME LEVEL)

2ND STAGE HEAT
NO
2ND STAGE
CALL FOR HEAT
SATISFIED?

YES
DE−ENERGIZE 2ND STAGE
GAS VALVE

INDUCER SPEED SWITCHED
TO LOW SPEED

INDOOR BLOWER SWITCHED
TO LOW HEAT SPEED

1ST STAGE HEAT
NO
1ST STAGE
CALL FOR HEAT
SATISFIED?

YES
GAS VALVE
DE−ENERGIZED

INDUCER OFF AFTER
5 SECOND POST PURGE

INDOOR BLOWER OFF
AFTER FIELD SELECTABLE
OFF DELAY

Page 70

Troubleshooting: Cooling Sequence of Operation (Continued)
CALL FOR COOLING
1
1ST STAGE COOLING
REQUEST RECEIVED 1

WAIT FOR COMPRESSOR TIMED
OFF DELAY TO EXPIRE

ENERGIZE 1ST STAGE
COOLING CONTACTOR
(COMPRESSOR & FAN)
INDOOR BLOWER 2
SECOND ON DELAY
ENERGIZE INDOOR BLOWER
2
(LOW COOLING MODE)

MAINTAIN INDOOR
BLOWER
(LOW COOLING MODE)
1
2ND STAGE
COOLING
REQUEST?
YES
ENERGIZE 2ND STAGE
COOLING CONTACTOR
(COMPRESSOR & FAN)

YES
YES
1ST STAGE
COOLING REQUEST
STILL ACTIVE?

YES
ENERGIZE INDOOR BLOWER
2
(HIGH COOLING MODE)
NO

2ND STAGE
COOLING REQUEST
STILL ACTIVE?

YES

MAINTAIN INDOOR BLOWER
(HIGH COOLING MODE)

YES

ENERGIZE AND MAINTAIN
INDOOR BLOWER AT
(LOW COOLING MODE)

NO
DE−ENERGIZE 2ND
STAGE COOLING
CONTACTOR
(COMPRESSOR & FAN)

1ST STAGE
COOLING REQUEST
STILL ACTIVE?

DE−ENERGIZE 1ST
STAGE COOLING
CONTACTOR
(COMPRESSOR & FAN)

1 CONTROL WILL NOT RESPOND TO A 2ND STAGE COOLING REQUEST UNLESS A 1ST STAGE
COOLING REQUEST IS ACTIVE.

2
DE−ENERGIZE INDOOR
2
BLOWER

INDOOR BLOWER LOW COOLING MODE AND HIGH COOLING MODE HAVE SPECIFIC ON, OFF
AND SPEED RAMPING PROFILES. THE SPECIFIC PROFILE IS SELECTED USING THE
DIP SWITCHES ON THE CONROL.

Page 71

Troubleshooting: Continuous Fan Sequence of Operation
CALL FOR FAN
1

CALL FOR FAN

INDOOR BLOWER ON
CONTINUOUS FAN
SPEED

CALL FOR FAN
REMOVED?

MAINTAIN INDOOR
BLOWER AT
CONTINUOUS FAN

YES

REQUEST
FOR COOLING
RECEIVED?

YES

MAINTAIN INDOOR
BLOWER AT
CONTINUOUS FAN

GO TO CALL FOR COOLING

INDOOR BLOWER OFF

GO TO CALL FOR 1ST STAGE HEAT

REQUEST
FOR HEAT
RECEIVED?

YES

DE−ENERGIZE INDOOR
BLOWER

Page 72

Source Exif Data:

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Author                          : tjp
Create Date                     : 2011:06:16 14:42:30-05:00
Modify Date                     : 2011:06:16 14:47:15-05:00
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Metadata Date                   : 2011:06:16 14:47:15-05:00
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Title                           : 506763a
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Instance ID                     : uuid:3a68e103-c3ee-48a4-8aaa-e7dbb78ba389
Page Count                      : 72

EXIF Metadata provided by EXIF.tools

Lennox International Inc Furnace Dave Signature Collection Gas Upflow Horizontal Air Dis 506763a

Lennox International Inc. Furnace SL280UH070V36A Lennox_SL280UHV_IOM

DAVE LENNOX SIGNATURE COLLECTION GAS FURNACE UPFLOW HORIZONTAL AIR DISCHARGE to the manual 33807615-f9a6-4b72-ba73-52431e7cefef

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