LENNOX Furnace/Heater, Gas Manual L0806183

User Manual: LENNOX LENNOX Furnace/Heater, Gas Manual LENNOX Furnace/Heater, Gas Owner's Manual, LENNOX Furnace/Heater, Gas installation guides

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INSTALLATION
INSTRUCTIONS

E Wvm)
®
,t,: 2005 Lennox industries inc.
Dallas, Texas, USA

G51MP SERIES UNITS
GAS
U.iTS

qT_bb
Teoho,ca,

505,065M
07/07
Supersedes 07/2005

_L_ Publications
Lithe U.S.A.

Unit Dimensions ...............................
G51MP Parts Identification ......................
Shipping and Packing List .......................
Safety Information ..............................
General .......................................
Combustion, Dilution & Ventilation Air .............
Installation - Setting Equipment ..................
Filters ........................................
Duct System ..................................
Pipe & Fittings Specifications ...................
Vent Piping Guidelines .........................
Joint Cementing Procedure .....................
Venting Practices .............................
Gas Piping ...................................
Electrical .....................................
Unit Start-Up .................................
Gas Pressure Adjustment ......................
High Altitude Information .......................
Other Unit Adjustments ........................
Service ......................................
Repair Parts List ..............................
Ignition Control Board Diagnostic Codes .........
Troubleshooting ...............................
Vent Pipe Sizing Worksheet ....................
Start-Up & Performance Check List ..............

RETAIN THESE INSTRUCTIONS
FOR FUTURE REFERENCE

2
3
4
4
6
6
8
16
16
16
18
19
19
30
33
37
38
39
40
41
43
43
44
48
48

AWARNING

Do not store or use gasoline or other
flammable
vapors and liquids in the
vicinity
of this or any other appliance.
Installation
and service
must be
performed
by a qualified installer,
service agency or the gas supplier.

WHAT TO DO IF YOU SMELL

• Do not try to light any appliance.
• Do not touch any electrical switch; do not
use any phone in your building.
• Leave the building immediately.
• Immediately
call your gas supplier from a
neighbor's phone. Follow the gas supplier's
instructions.
• If you cannot reach your gas supplier, call
the fire department.

07/07

IIIlllllllllllllllllllllllllllllllllllll

GAS:

505,065M
Page 1

IIIIIIIIIIIIIIIIIIIIIIIIIIIIII

*NOTE - 60C and 60D size units installed in upflow applications that require air volumes over 1800 cfm (850 L/s) must
have one of the following:
1. Single side return air with transition, to accommodate
20 x 25 x 1 in. (508 x 635 x 25 mm) air filter.
Required to maintain proper air velocity.
2. Single side return air with optional RAB Return Air Base
3. Bottom return air.
4. Return air from both sides.
5. Bottom and one side return air.
Refer to Engineering Handbook for additional information.

1 Optional External Side Return Air Filter Kit is not for use
with the optional RAB Return Air Base.

A -_

9v-----

B -_

9-9/16

/=_-

_OPTIONAL
EXTERNAL
SIDE RETURN
AIR FILTER KIT
(Either Side)

**Consider sizing requirements for optional IAQ equipment
before cutting side return opening.

SUPPLY AIR
OPENING

(14)

5-1/2

23-3/4
I.........
I_

za _o._a/

TOP VIEW
I_

28 -1/2

(724)

_._

$
6-1/2

(803)

_._1._

r_
....

19-7/16

9/16
'q'- (14)

._1_

COMBUSTION AIR INTAKE
_
(Either Side)

11-5/8
(295) Right
9-3/4 (248)
Left

1 OPTIONAL
EXTERNAL
SIDE RETURN
AIR FILTER KIT
(Either Side)

4-1/8

( I )/
9- _/_

6-3/4

\
._

(103) (171)

EXHAUST AIR OUTLET
(Either Side)

.. GAS
PIPING
INLET

_ll_._f\_.
_)_
tJ
L

4-7/8 (124) Right
2-1/4 (57) Left -I_

40
(1016)

(Either Side)
\

.r_ CONDENSATE
TRAPCONNECTION

°Oo--___"

(Either Side)
_

ELECTRICAL

_p_.ql__

04I

-23

INLET

(Either side )

(64)
A 2-1/2
18-3/4

.__

{102

(476)

"
I
I

(584)
*OPTIONAL
RETURN CUTOUT
(Either Side)

I
14"*
(356)

AIR FLOW
1-15/16

Jl.--c
3/4 (19)

*Bottom Return
Air Opening

4-1/4
(108)

*Bottom Return
Air Opening

FRONT VIEW

SIDE VIEW

A
Model No.

(49)

5/8(16)
314(19)

in.

G51MP-24B-045
G51MP-36B-045
G51MP-36B-070

17-1/2

446

16-3/8

416

406

G51 MP-36C-090
G51MP-48C-090
G51MP-60C-090
G51MP-48C-110
G51MP-60C-110

533

19-7/8

454

19-1/2

495

G51MP-60D-135

24-1/2

622

23-3/8

546

584

Page 2

G51MP

PARTS

IDENTIFICATION

DuralokPlus TM
HEATEXCHANGER
ASSEMBLY
CABINET

GAS VALVE
AND MANIFOLD

FLUE
COLLAR

COMBUSTION
AIR PRESSURE
PROVE SWITCHES

WARM HEADER
(COLLECTOR)
BOX

CONDENSER
BURNER
ACCESS
PANEL

PRIMARY LIMIT

,/_
/
BLOWER
ACCESS
DOOR

COLD HEADER
(COLLECTOR)
BOX

DOOR
INTERLOCK
SWITCH

SECONDARY
LIMITS (2)

BLOWER
ASSEMBLY

SIGHT
GLASS
CONTROL BOX

FIGURE 1

Page 3

COIL

TheG51MPgasfurnaceisshippedreadyforinstallation
in
theupflow,downflow,
horizontal
leftairdischarge
or horizontalrightairdischargeposition.Thefurnaceis shipped
withthebottompanelin place.Thebottompanelmustbe
removedif theunitis tobeinstalledin upflowapplications
withbottomreturnair.Thebottompanelmustalsoberemovedanddiscarded
inalldownflow
orhorizontal
applications.
Thefurnaceis equippedforinstallation
in naturalgasapplications.
A conversion
kit(ordered
separately)
is required
forusein propane/LP
gasapplications.

NOTE - G51MP-48C-110 and G51MP-60C-110 units also
include a 2" diameter ABS street elbow, which is shipped
on the blower deck in the heating compartment.
G51MP-60D-135 units are shipped with a 3" to 2"ABS reducing elbow.
The following items may also be ordered separately:
1- Thermostat
1 - Propane/LP changeover kit
Check equipment for shipping damage. If you find any
damage, immediately contact the last carrier.

&WARNING

The G51MP can be installed as either a Direct Vent or a
Non-Direct Vent gas central furnace.
NOTE - In Direct Vent installations, combustion air is taken
from outdoors and flue gases are discharged outdoors. In
Non-Direct Vent installations, combustion air is taken from
indoors and flue gases are discharged outdoors. See figure 2 for applications involving roof termination.
DIRECT
VENT
COMBUSTION
AIR iNTAKE
OUTSIDE OF

INSTALLATION
I
r

&CAUTION

NON-DIRECT VENT
INSTALLATION

EXHAUST
OUTLET

'EXHAUST
OUTLET

HOUS_

COMBUSTION
AiR iNTAKE
INSIDE
OF

HOUSE

Use only the type of gas approved for use with this furnace.
Refer to unit nameplate.
G51MP units are CSA International certified to ANSI
Z21.47 and CSA 2.3 standards.
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

DRAIN
CONDENSATE
DRAIN

FIGURE 2

Gas Code (ANSl-Z223.1/NFPA
54). The National Fuel
Gas Code is available from the following address:
American National Standards Institute, Inc.
11 West 42nd Street
New York, NY 10036
In Canada, installation must conform with current National

Package 1 of 1 contains
1 - Assembled G51MP unit
1 - Bag assembly containing the following:
3 - Screws
3 -Wire nuts
1 - Snap bushing
1 - Snap plug
1 - Wire tie
1 - Condensate trap
1 - Condensate trap cap
2 -2" diameter vent / intake plugs
1 - 3" diameter cabinet plug (intake)
1 -2" diameter debris screen

Standard of Canada CSA-B149 Natural Gas and Propane
Installation Codes, local plumbing or waste water codes
and other applicable local codes.
In order to ensure proper unit operation in non-direct vent
applications, combustion and ventilation air supply must be
provided according to the current National Fuel Gas Code
or CSA-B149 standard.
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, 12 and 16. 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.
Page 4

Forinstallation
ina residential
garage,thefurnacemustbe
installedso thattheburner(s)andtheignitionsourceare
locatednolessthan18inches(457mm)abovethefloor.
Thefurnacemustbelocatedor protected
toavoidphysical
damagebyvehicles.
Whena furnaceis installed
ina public
garage,hangar,or otherbuildingthathasa hazardous
atmosphere,
thefurnacemustbeinstalled
according
torecommended
goodpracticerequirements
andcurrentNationalFuelGasCodeor CSAB149standards.
NOTE - Furnace must be adjusted to obtain a temperature
rise within the range specified on the unit nameplate. Failure to do so may cause erratic limit operation and premature heat exchanger failure.
This G51MP furnace may be used as a high-static unit
heater. The G51MP may also be installed in an aircraft
hangar in accordance with the Standard for Aircraft Hangars (ANSI/NFPA No. 408-1990).
Installation in parking structures must be in accordance
with the Standard for Parking Structures (ANSI/NFPA No.
88A-1991 ). Installation in repair garages must be in accordance with the Standard for Repair Garages (ANSI/NFPA
No. 88B-1991 ).
This G51MP furnace must be installed so that its electrical
components are protected from water.
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.
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.
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
(ANSl/NFPA No. 70) is available from the following address:
National Fire Protection Association
1 Battery March Park
Quincy, MA 02269
In Canada, all electrical wiring and grounding for the unit
must be installed according to the current regulations of the
Canadian Electrical Code Part I (CSA Standard C22.1)
and/or local codes.
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

Page 5

night setback thermostat is used. Return air temperature
must not exceed 85°F (29°C) dry bulb.
The G51MP furnace may be installed in alcoves, closets,
attics, basements, garages, and utility rooms.
This furnace design has not been CSA certified 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.
Lennox does not recommend the use of G51MP 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.
G51MP units may be used for heating of buildings or structures under construction, if the following conditions are
met:
• 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 inputrate and temperature rise mustbe setperthe
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.
NOTE - The Commonwealth
of Massachusetts
stipulates these additional requirements:
• Gas furnaces shall be installed by a licensedplumber or gas 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.

Theseinstructions
areintended
asa generalguideanddo
notsupersede
localcodesinanyway,Consultauthorities
havingjurisdictionbeforeinstallation.
Inadditiontotherequirements
outlinedpreviously,
thefollowinggeneralrecommendations
mustbe considered
wheninstallinga G51MPfurnace:
• Placethefurnaceas closeto thecenterof theairdistributionsystemaspossible.
Thefurnaceshouldalsobe
locatedclosetothechimneyorventtermination
point,
• Whenthefurnaceis installed
innon-direct
ventapplications,donotinstallthefurnacewheredraftsmightblow
directlyintoit,Thiscouldcauseimpropercombustion
andunsafeoperation,
• Whenthefurnaceis installed
innon-direct
ventapplications,donotblockthefurnacecombustion
airopening
withclothing,boxes,doors,etc.Airisneededforproper
combustion
andsafeunitoperation.
• Whenthefurnaceis installedin anatticor otherinsulatedspace,keepinsulationawayfromthefurnace,
• Whenthe furnaceis installedin an unconditioned
space,considerprovisions
requiredtopreventfreezing
ofcondensate
drainsystem,

If the G51MP is installed as a Non-Direct Vent Furnace,
follow the guidelines in this section.
NOTE- In Non-Direct Vent installations, combustion air is
taken from indoors and flue gases are discharged outdoors.

,& WARNING

,& CAUTION

-&WARNING

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 po-tentially dangerous situation,
In the absence of local codes concerning air for combustion and ventilation, use the guidelines and procedures in
this section to install G51MP furnaces to ensure efficient
and safe operation. You must consider combustion air
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-

Page 6

Z223.1/NFPA
54).Thisreprintedmaterialis notthecompleteandofficialpositionof the ANSIon thereferenced
subject,whichis represented
onlybythestandard
initsentirety.
InCanada,referto theCSAB149installation
codes.

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.

,&CAUTION

All gas-fired appliances require air for the combustion process. If sufficient combustion air is not available, the furnace or other appliance 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
same time as the furnace, much more air
sure proper combustion and to prevent a
ficient air causes incomplete combustion
in carbon monoxide.

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 airmust be handled by ducts
which are sealed to the furnace casing and which terminate
outside the space containing the furnace. This is especially

are used at the
is required to endowndraft. Insufwhich can result

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 mm 2) 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 3.

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.

EQUIPMENT

EXHAUST

IN CONFINED

SPACE - ALL AIR FROM INSIDE

PIPE

ROOF TERMINAl

_1_
ED

The requirements for providing air for combustion and ventilation depend largely on whether the furnace is installed in
an unconfined or a confined space.

__,_

f--

Unconfined

SIDE WALL
ERMINATED
EXUST PIPE (ALTER-

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
com-bined input rating of all appliances installed in that
space. This definition includes furnace closets or small
equipment rooms.

Page 7

ATE LOCATION)

Ill

,, ,,

,,
I

OPENINGS
(To Adjacent
Unconfined

__pace)

G51MP

.........
I

, ,,
I

I°

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

FIGURE 3
Air from Outside
If air from outside is brought in for combustion and ventilation, the confined space shall be provided with two permanent openings. One opening shall be within 12" (305mm) of
the top of the enclosure and one within 12" (305mm) 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 per 4,000 Btu (645mm 2 per 1.17kW) per hour
of total input rating of all equipment in the enclosure. When
communicating with the outdoors through horizontal ducts,

eachopeningshallhavea minimum
freeareaof1 square
inchper2,000Btu(645mm
2per.59kW)pertotalinputratingofallequipment
in theenclosure(Seefigure4),

EQUIPMENT

EQUIPMENT IN CONFINED SPACE - ALL AIR FROM OUTSIDE
(Inlet Air from Crawl Space and Outlet Air to Ventilated Attic)

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

7
ROOF TERMINATED
EXHAUST PIPE

VENTILATION
ROOF TERMINATED
EXHAUST PIPE

LOU-

VERS
(Each end of attic)

OUTLET
AIR

SIDE WALL
TERMINATED
EXHAUSTPIPE
(ALTERNATE
LOCATION)

VENTILATION
LOUVERS
(Each end of attic)

INLET

INLET AIR
(Ends 12"above
bottom)

TERMINATED
EXHAUSTPtPE
(ALTERNATE
LOCATION)
VENTILATION
LOUVERS
(For unheated
crawl space)

NOTE-The inlet and outlet air openings shall each have a free area of
at least one square inch per 4,000 Btu (645mm2per 1.17kW) per hour
of the total input rating of all equipment in the enclosure.

FIGURE 5
NOTE-The inlet and outlet air openings shall each have a free area
of at least one square inch per 4,000 Btu (645mm 2per 1.17kW) per
hour of the total input rating of all equipment in the enclosure.

EQUIPMENT IN CONFINED SPACE ALL AIR FROM OUTSIDE

FIGURE 4

ROOF TERMINATED
EXHAUST PIPE

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 mm 2) per 4,000 Btu (1,17
kW) per hour of total input rating of all equipment in the enclosure. See figures 4 and 5. When communicating with
the outdoors through horizontal ducts, each opening shall
have a minimum free area of 1 square inch (645 mm 2) per
2,000 Btu (.56 kW) per total input rating of all equipment in
the enclosure, See figure 6,
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,

SIDE WALL
TERMINATED
EXHAUSTPIPE
(ALTERNATE
LOCATION)

NO TE-Each air duct opening shall have a free area of at least one
square inch per 2,000 Btu (645mm2per. 59kW) 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 1 square inch per 4, 000 Btu (645mm 2per 1.17kW) per
hour of the total input rating of all other equipment in the enclosure.

FIGURE 6

Page 8

-&WARNING

Selecta locationthatallowsfor therequiredclearances
thatarelistedonthe unitnameplate.
Alsoconsidergas
supplyconnections,
electricalsupply,vent connection,
condensate
trap anddrainconnections,
andinstallation
andserviceclearances
[24inches(610mm)atunitfront].

Installation Clearances
Top

The unit must be level from front to back and side to side.
Left Side

NOTE - 1/3 hp blower motors are equipped with four flexible mounting legs, and 1/2 hp blower motors are equipped
with three flexible legs and one rigid leg. 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.
Allow for clearances to combustible materials as indicated
on the unit nameplate. Minimum clearances for closet or alcove installations are shown in figures 7, 12 and 16.

WARNING

Right Side
J

Bottom (Floor)
...............................................

T ...............................................

Top/Plenum

i
t
i

*Front

1 in. (25 ram)
O

."................... ....................
T......................
........................
,,'
.....................-.........................f...............................................
I
Vent

Floor

O:_

*Front clearance in alcove installation must be 24 in. (610 ram).
Maintain a minimum of 24 in. (610 ram) for front service access.
tAllow proper clearances to accommodate condensate trap and
vent pipe installation.
! :_For installations on a combustible floor, do not install the furi nace directly on carpeting, tile or other combustible
materials othi er than wood flooring.

=================================================================================================

FIGURE 7
Return Air -- Upflow

Units

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

A WARNING

panel to facilitate installation,
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 - When air volumes over 1800 cfm (850 L/s) are
required with 60C or 60D models in an upflow application, the following return air options are available:
1 - Return

air from

accommodate
(Required
2 - Return

Upflow

The G51MP gas furnace can be installed as shipped in the
upflow position. Refer to figure 7 for clearances.

Page 9

side

to maintain
air from

Air Base.

Applications

single

with

transition

which

will

20 x 25 x I in. (508 x 635 x 25 ram) air filter.
proper

single

See figure

side

air velocity.)
with

optional

one

side.

10.

3 - Return

air from

bottom.

4 - Return

air from

both

5 - Return

air from

bottom

sides.
and

See figure
RAB

Return

Refer to Engineering Handbook for additional information.

Removing the Bottom Panel

G51MP applications which include side return air and
a condensate trap installed on the same side of the
cabinet require either a return air base or field-fabricated transition to accommodate an optional IAQ accessory taller than 14.2".

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 9,
Removing the Bottom Panel

Side Return Air
(with transition and filter)

20" X 25" X 1"
(508mm X635mm X 25mm)
Air Filter

Screw
Return
Air
Plenum

\./
Bottom Cap
Bottom

FIGURE 8

FIGURE 9
Optional Return Air Base

-I_

4 I
(102)r 91"--

AIR FLOW
.................................................................................. FURNACE
FRONT

7-1/4

17-1/2

21 (533)
24-1/2

_
(98M60)

(446) RAB-B
RAB-C

(98M58)

(622) RAB-D

(98M59)

1 Minimu"-_

(Maximum)
11 (279) I
Maximun_
I1Unit side return air 1
6)
Opening

J,
L

5-5/8
t143_

(184)

"
_

-fL

1 23 (584)
Overall

OPTIONAL
RAB
RETURN
AiR BASE

ql_

|
_ i

(Either

(570)
Overall
Maximum)

SIDE RETURN
AiR OPENINGS
"

1 22-7-16

Side)

23 (584)

3/4
(19)

7/8

-I_

(22)

_1--

27-5/8

(702)

SIDE

VIEW

FRONT VIEW
NOTE- Optional Side Return Air Filter Kits are not for use with RAB 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.
NOTE- Optional Side Return Air Filter Kits are not for use with RAB Return Air Base.

FIGURE 10
Page 10

Levelingan

Upflow Unit

When the side return air inlets are used in an upflow application, it may be necessary to install leveling bolts on the
bottom of the furnace. Use field-supplied corrosion-resistant 5/16 inch machine bolts (4) and nuts (8). See figure 11.

Refer to figure 12 for clearances
tions.

in downflow applica-

• ...............................................................................................

Downflow Application Installation Clearances
Top

NOTE - The maximum length of the bolt is 1-1/2 inches.
1 - Lie the furnace on its back and drill a 5/16 inch diameter hole in each corner of the furnace's bottom. See figure 11 for the correct location of the holes. Drill through
the bottom panel and the bottom flange of the cabinet.
2 - Install one bolt and two nuts into each hole. Screw the
first nut onto a bolt and then insert the bolt into a hole. A

Left Side

Right Side

flat washer may be added between the nut and the bottom of the unit.
3 - Screw another nut onto the bolt on the inside of the fur-

Bottom
&
...............................................

nace base. A flat washer may be added between the
nut and the bottom of the unit.
4 - Adjust the outside nut to the appropriate height and
tighten the inside nut to secure the arrangement.

,I
T ...............................................

Top

*Front

."................... ....................
T......................
........................
Sides

NOTE - The unit may be tilted back-to-front a maximum of
1". This will ensure proper draining of the heat exchanger.

i
]
i

Vent
...............................................

Inches

Furnace Front

_¢

3/8

NC_:

*Front clearance in alcove installation must be 24 in. (616 ram).
Maintain a minimum of 24 in. (610 ram) for front service access.
tAllow proper clearances to accommodate
condensate
trap and
vent pipe installation.
_:The furnace may be installed on a combustible
wood floor if an
i optional additive base is installed between the furnace and the

Bolt Installation
3/8

t ................................................

Floor

Leveling

(mm)

1-3/4
(44)

i combustible

floor.

=================================================================================================

FIGURE 12
Installation on Non-Combustible

1-3/4
(44)

Leveling

1 - Cut floor opening keeping in mind clearances listed on
unit rating plate. Also keep in mind gas supply connec-

Leveling Bolt
Locations

Furnace
Bottom

tions, electrical supply, flue and air intake connections
and sufficient installation and servicing clearances.
See table 1 for correct floor opening size.
2 - Flange warm air plenum and lower the plenum into the
opening.
3 - Set the unit over the plenum and seal the plenum to
the unit.

3/8

Bolt

(1o)

3/8
(10)

1-3/4
(44)

3 - Ensure that the seal is adequate.
TABLE 1
NON-COMBUSTIBLE
FLOOR OPENING SIZE

I-3/4 (44)

i............................
[......
'ronno'......
e;r"
[......

FIGURE 11

Downflow

Flooring

Applications

Model No.

I_.................................
In.
I
mm
i

The unit may be installed three ways in downflow applications: on non-combustible flooring, on combustible flooring
using an additive base, or on a reverse-flow cooling cabinet. Do not drag the unit across the floor in the downflow position. Flange damage will result.

Page 11

jBCabinet(17.5")

i19-3/4,

jCCabinet(21")

,i 19-3/4

••

•

,i 16-5/8

-I.,

I_.................................
In.
I
mm
-I.,

502
502

........
i
ii

20-1/8

-I.,

422

511

i............................
[................
L................
[................
[................
i
•
• DCabmet(245)

3/4

502

, 23

5/8

600

NOTE - Floor opening dimensions listed are 1/4 inch (6 mm) larger than
the unit opening. See dimension drawing on page 2.

•

Installation on Combustible

Flooring

Installation

1 - When unit is installed on a combustible floor, an additive base must be installed between the furnace and

on Cooling

Cabinet

1 - Refer to reverse-flow coil installation instructions for

the floor. The base must be ordered separately for the
following cabinet sizes:
• B cabinet 17,5" - # 11M60
• C cabinet21"-#
11M61
• D cabinet 24,5" - # 11 M62

correctly sized opening in floor and installation of cabinet,
2 - When cooling cabinet is in place, set and secure the
furnace according to the instructions that are provided
with the cooling coil, Secure the furnace to the cabinet,
3 - Seal the cabinet and check for air leaks.

See table 2 for opening size to cut in floor.

Return Air Opening

Ak CAUTION

-- Downflow

Units

The following steps should be taken when installing plenum:
1 - Bottom edge of plenum should be flanged with a
hemmed edge (See figure 14 or 15).
2 - Sealing strips should be used to ensure an airtight seal
between the cabinet and the plenum.

TABLE 2
ADDITIVE BASE FLOOR OPENING SIZE
Frontto

Rear

Side to Side

PLENUM

Model
in.

in.

B Cabinet

(17.5")

559

18 - 3/4

476

C Cabinet

(21")

559

22 - 3/4

578

D Cabinet

(24.5")

559

25 - 3/4

654

---,,_

(Field Provided)

_11 '''_

•

SECURE FROM

_UTSIDE

SEAL,NG
STR,

2 - After opening is cut, set additive base into opening.

(Field Provided)

3 - Check fiberglass strips on additive base to make sure
they are properly glued and positioned,

CABINET

II _

CABINET

IlJ S,DE
PANEL

......

Side View

FIGURE 14

4 - Lower supply air plenum into additive base until plenum flanges seal against fiberglass strips.

PLENUM
(Field P rovided_-..h.

NOTE - Be careful not to damage fiberglass strips,
Check for a tight seal,

_'_
SEALING
,_Field

5 - Set the furnace over the plenum.
6 - Ensure that the seal between the furnace and plenum
is adequate.

j
,

SECURE FROM
INSIDE CABINET

STRIP

Provided)

CABINET
SIDE PANEL

Side View
FIGURE 15

SUPPLY AIR PLENUM
G51MP UNIT_
PROPERLY

3 - In all cases, plenum should be secured to top of furnace using sheet metal screws,
4 - Make certain that an adequate seal is made.

__T

,VE
BASE

FIGURE 13

Page 12

Horizontal

Installation of Horizontal Furnace

Applications

The G51MP furnace can be installed in horizontal applications with either right- or left-hand air discharge.
Refer to figure 16 for clearances in horizontal applications,
H===================mmmmmmHHHmmmmmmHHHmmmmmmHHHmmmmmmHHHm.

Horizontal Application
Installation Clearances

Suspended in Attic
NOTE - If unit is suspended in attic or crawl space, horizontal support kit (Cat No 56J18 ordered separately) must be
used to ensure proper unit support and coil drainage.
1 - Select location for unit keeping in mind service and
other necessary clearances, See figure 16.

Right-Hand Discharge

2 - Provide service platform in front of unit,

Top

3 - Fabricate a drain pan fitted with a 1/2 inch or 3/4 inch
N,P,T, fitting.

Left
End

Right End

Using 3/8 inch rods and support frame kit (ordered
separately), fabricate suspension hangers for unit
keeping in mind front service access clearances.

5 - Mount unit on support frame as shown in figure 17.
Unit must be level to ensure proper coil drainage,

Left-Hand Discharge
Top

6- Continue with exhaust, condensate

and intake line

piping instructions,
Left
End

Right End

BLOWER ACCESS
INTAKE/EXHAUST
CONNECTION

Top

]

Back

PAN-

3/8 in. RODS

i...................
ron;:
...................
i......................
.......................
i
".................... ....................
i"i ......................
........................
=

Vent

....................
" oor"
...................
T.....................
;;.......................
| ...............................................

_ ................................................

*Front clearance in alcove installation must be 24 in. (610 ram).
Maintain a minimum of 24 in. (610 ram) for front service access.
**A 5-1/2" service clearance must be maintained below the unit to
provide for servicing of the condensate trap.
_:For installations on a combustible floor, do not install the furnace directly on carpeting, tile or other combustible materials other than wood flooring.

FIGURE 16
This furnace may be installed in either an attic or a crawlspace. The G51MP may also be installed as a unit heater.
Either suspend the furnace from roof rafters or floor joists,
as shown in figure 17, or install the furnace on a platform,
as shown in figure 18. The unit must be supported at both
ends and beneath the blower deck to prevent sagging,
NOTE -In horizontal applications, the unit must be level side to side. The unit may be tilted back to front a maximum of 1': This willensure proper draining of the heat exchanger.

Page 13

DRAIN PAN
SUPPORT

FRAME

(to protect

finished space)

FIGURE 17
7 - Hang drain pan below support frame as shown in figure 17. Leave 5-1/2 inches for service clearance below unit for condensate trap,
8 - Route auxiliary drain line so that water draining from
this outlet will be easily noticed by the homeowner,
Platform

Installation

of Horizontal

Unit in Attic

1 - Select location for unit keeping in mind service and
other necessary clearances. See figure 16,
2 - Construct a raised wooden frame and cover frame
with a plywood sheet, Provide a service platform and
drain pan for unit,

TYPICAL

HORIZONTAL

APPLICATION

(FORCED

INTAKE

WASHER

AIR FURNACE)
\

Xx\
EXHAUST
PIPE

AND 2 NUTS

BRACED FOR
SUPPORT

DRAIN PAN
(to protect
LAG BOLT

SUPPORT

............

finished
space)

ROD

*Gas connector may be used for Canadian
installation if acceptable by the local authority that has jurisdiction.
NOTE - Condensate trap and condensate line
must be protected by self-regulating heating
cable and insulation when run through unconditioned spaces.

SUPPORT
FRAME

BLOWER ACCESS
PANEL

FIGURE 18
EXHAUST

PIPE

INTAKE

*GAS
CONNECTOR

*Gas connector ma
used
for
Canadian
installation
ff acceptable by local authority
having judsdJction.

2 - Using 3/8 inch rods and support frame kit, fabricate
suspension hangers keeping in mind service access
panel clearances,
3 - Install unit on support frame as shown in figure 20. Unit
must be level to ensure proper coil drainage, Leave
5-1/2 inches for service clearance below unit for condensate trap.

RAISED

CONDENSATE
LINE

INTAKE

SERVICE PLATFORM

SUPPORT

PIPE

FIGURE 19

FRAME

3 - Route auxiliary drain line so that water draining from
this outlet will be easily noticed by the homeowner.
4 - Set unit in drain pan as shown in figure 19. Unit must
be level to ensure proper coil drainage, Leave 5-1/2
inches for service clearance below unit for condensate
trap,
5 - Continue with exhaust, condensate and intake piping

FIGURE 20
4 - Install exhaust and intake piping according to instructions given in following section. Condensate line
should be run into condensate pump if necessary to
meet drain line slope requirements.
Platform Installation of Horizontal

installation according to instructions.
Installation of Horizontal Unit
Suspended in Crawl Space
NOTE - If unit is suspended in attic or crawl space, support
frame kit (Cat No 56J18 ordered separately) must be used
to ensure proper unit support and coil drainage.
1 - Select location for unit keeping in mind service and
other clearances, See figure 16,

Unit in Crawl Space
1 - Select location for unit, keeping in mind service and
other clearances,
2 - After positioning cement blocks, mount support frame
kit (Cat No 56J18 ordered separately) on top of blocks
and install unit on frame. Unit must be level to ensure
proper heat exchanger coil drainage. Leave 5-1/2
inches for service clearance) for condensate trap,

Page 14

ternal components of unit heater when drilling holes or
installing screws. See figure 23,
5 - Use adjustable, double-deflection grille(s) to distribute
discharge air. Adjust static pressure to be in the 0,06
inch to 0,10 inch w,c, range,

INTAKE
PIPE

EVAPORATOR

COIL

DRAIN PAN

FIGURE 21

(to protect '_
finished

3 - Install exhaust and intake piping according to information given in following section. Condensate line should
be run into condensate pump as shown in figure 21,
G51MP Installed in Unit Heater Applications
Horizontal unit heaters may be installed either suspended
from the ceiling using the support frame kit or mounted on a
field-fabricated platform. The condensate trap must be
installed where it can be serviced at a later date,
Unit Heater Discharge Duct Guidelines
A field-fabricated and installed discharge air duct and grille
cabinet is suitable for use with the G51MP heater, See figure 22. Keep the following items in mind when constructing
the cabinet.
1 - Outer dimensions of cabinet should match those of the
unit heater, so the duct/grille cabinet installs flush with
the unit heater cabinet. See figure 22.
2 - Flange both ends of duct/grille cabinet so that screws
can be used to secure cabinet to discharge end of unit
heater.
DISCHARGE AIR DUCT/GRILLE
18in. (457 mm) Ik

space)
NOTE - When installing duct/grille cabinet, take care not to damage internal unit
heater components
when dnlhng holes or installing screws.

FIGURE 23
Installation of Horizontal Unit Heater
Suspended from Ceiling
1 - Select location for unit keeping in mind service and
other clearances.
2 - Fabricate a drain pan fitted with 1/2 inch (13 mm) or
3/4 inch (19 mm) N.P.T. fitting.
3 - Using 3/8 inch (9 mm) rods and support frame kit (ordered separately), fabricate suspension hangers,
keeping in mind service access panel clearances.
4 - Hang drain pan below support frame as shown in figure 23, Route auxiliary drain line so that water draining from this outlet will be easily noticed by the homeowner,
5 - Mount unit on support frame as shown in figure 23.
Unit must be level to ensure proper coil drainage.
Leave 5-1/2 inches for service clearance below unit for
condensate trap,

CABINET

6- Continue with exhaust, condensate
piping instructions.
Platform

Installation

of Horizontal

and intake line
Unit Heater

1 - Select location for unit keeping in mind service and
other necessary clearances.
2 - Construct a raised wooden frame and cover frame
with a plywood sheet. Provide service platform and

FIELD-FABRICATE

drain pan for unit, Route auxiliary drain line so that water draining from this outlet will be easily noticed by the
homeowner,

GRILL CABINET

TO DESIRED DIMENSION

FIGURE 22
3- To ensure proper operation, the duct/grille
must be at least 18 inches long,

cabinet

3 - Set unit in drain pan as shown in figure 24, Unit must
be level to ensure proper coil drainage, Leave 5-1/2
inches for service clearance below unit for condensate
trap.

4 - Use #10-16 x 1/2 inch sheet metal screws to secure
duct/grille cabinet to unit, taking care not to damage in-

Page 15

4 - Continue with exhaust, condensate and intake piping
installation according to instructions which follow.

er), 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.

*GAS CONNECTOR
INTAKE
*Gas connector may be
used for Canadian installation ff acceptable by bca/authority
having junsdiction.

PIPE

Return air can be brought in through the bottom or either
side of the furnace, If a furnace with bottom return air is
RAISE
CONDENSATE

LINE

PLATFORM

FIGURE 24
Return Air -- Horizontal

Applications

Return air can 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 9.

This unit is not equipped with a filter or rack, A field-provided filter is required for the unit to operate properly, Table
3 lists recommended filter sizes,
A filter must be in place whenever the unit is operating,
TABLE 3
Furnace
Cabinet Size

Filter Size
Side Return

All pipe, fittings, primer and solvent cement must conform
with American National Standard Institute and the American Society for Testing and Materials (ANSI/ASTM) standards. The solvent shall be free flowing and contain no
lumps, undissolved particles or any foreign matter that adversely affects the joint strength or chemical resistance of
the cement. The cement shall show no gelation, stratification, or separation that cannot be removed by stirring. Refer to the table 4 below for approved piping and fitting materials.

Bottom Return

17-1/2"

16X25X

1(1)

16X25Xl(1)

21"

16X25X

1(1)

20X25Xl(1)

16X25X

1(2)

24X25Xl(1)

24-1/2"

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.

TABLE 4
PIPING AND FITTINGS SPECIFICATIONS
PIPE & FITTING MATERIAL
Schedule 40 PVC (Pipe)
Schedule 40 PVC (Cellular Core Pipe)

ASTM
SPECIFICATION
D1785
F891

Use industry-approved standards 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.

Schedule 40 PVC (Fittings)

D2466

SDR-21PVC

(Pipe)

D2241

SDR-26 PVC (Pipe)

D2241

NOTE - Operation of this furnace in heating mode (indoor
blower operating at selected heating speed) with an external static pressure which exceeds 0.5 inches w.c. may result in erratic limit operation.

Schedule 40 ABS Cellular Core DWV (Pipe)

F628

Schedule 40 ABS (Pipe)

D1527

Schedule 40 ABS (Fittings)

D2468

ABS-DWV (Drain Waste & Vent)
(Pipe & Fittings)

D2661

PVC-DWV (Drain Waste & Vent)
Pipe & Fittings)

D2665

Supply Air Plenum
If the furnace is installed without a cooling coil, a removable
access panel should be installed in the supply air duct, The
access panel should be large enough to permit inspection
(by 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
Return air must not be drawn from a room where this
furnace, or any other gas appliance (ie., a water heat-

Page 16

Ak CAUTION

Primersand solventsmustmeetASTMspecifications.
PVCprimeris specifiedinASTMF656.UsePVCsolvent
cementasspecified
inASTMD2564andABSsolventcementasspecifiedinASTMD 2235.Lowtemperature
solventcementis recommended.
Metalor plasticstrapping
maybe usedforventpipehangers,
WhenmakingABSjoints,piecescanbepreparedwitha
cleaner.WhenjoiningABStoPVCmaterials,
usePVCsolventcement,Referto the procedure
specifiedin ASTM
D3138,

vent cement used to vent this appliance must be certified to
ULC $636 and supplied by a single manufacturer as part of
an approved venting system. When bonding the vent system to the furnace, use ULC $636 approved One-Step
Transition Cement to bond the pipe to the flue collar, 90 °
elbow or reducing 90 ° elbow as applicable. In addition, the
first three feet of vent pipe from the furnace flue collar must
be accessible for inspection.

Table 5 lists the available exhaust termination kits, as well
as vent pipe equivalencies which must be used when sizing
Canadian Applications Only - Pipe, fittings, primer and solvent pipe. All Lennox vent terminations are PVC or ABS.
TABLE 5
OUTDOOR TERMINATION KITS AND CORRESPONDING EQUlVALENClES
Vent Pipe Length Equivalency (feet)

UNIT
MODEL

24B-045
36B-045

Outdoor
Exhaust
Accelerator
(Dia. X
Length)

1-1/2"
Concentric Kit

1-1/2" X 12"

2" X 12"

71M80

Not
Allowed

2-1/2

Outdoor
Exhaust
Accelerator
(Dia. X
Length)

2" Wall
Kit with
Vent Extension

2" Wall
Ring Kit

30G79

15F74

Not
Allowed

14"

Not
Allowed

14"

2" Concentric
Kit

3" Concentric
Kit

69M29

60L46

Not
Allowed

2-1/2

3
4

VENT
PIPE
DIA.
(in.)

36B-070

36C-090
48C-090
60C-090

48C-110
60C-110

***For

22G44
30G28

3" Wall
Plate Kit

44J40
81J20

Not
Allowed

1**

2-1/2

Not
Allowed

2**

Not
Allowed

2**

Not
Allowed

4**

Not
Allowed

1**

2-1/2

Not
Allowed

2***

Not
Allowed

2***

Not
Allowed

4***

Not
Allowed

6***

Not
Allowed

10"**

60D-135

*Requires
**Requires

2" Wall
Plate Kit

field-provided
field-provided

and installed 1-1/2" exhaust accelerator.
and installed 2" exhaust accelerator.

use only in non-direct

vent applications,

when snow riser is

Page 17

not required.
celerator.

Requires

field-provided

and installed

2" exhaust

ac-

The G51MP can be installed as either a Non-Direct Vent
or a Direct Vent gas central furnace.
NOTE - In Non-Direct Vent installations, combustion air is
taken from indoors and flue gases are discharged outdoors. In Direct Vent installations, combustion air is taken
from outdoors and flue gases are discharged outdoors.
Intake and exhaust pipe sizing in Direct Vent applications
and exhaust pipe sizing in Non-Direct Vent applications -Size pipe according to tables 6 and 7. Table 6 lists the minimum equivalent vent pipe lengths permitted. Table 7 lists
the maximum equivalent pipe lengths permitted.
Maximum vent length is defined as:
Total length (linear feet) of pipe,
Plus Equivalent length (feet) of fittings,
Plus Equivalent length (feet) of termination.
NOTE - Include ALL pipe and ALL fittings,
doors and outdoors.

both in

Regardless of the diameter of pipe used, the standard roof
and wall terminations described in section Exhaust Piping
Terminations should be used. Exhaust vent termination
pipe is sized to optimize the velocity of the exhaust gas as it
exits the termination. Refer to table 8.
*NOTE - The exhaust pipe should be offset a minimum of
12 inches to avoid the possibility of water droplets being released from the exhaust termination. The minimum exhaust vent length is 15 ft. Shorter exhaust vent lengths may
result in the discharge of water droplets from the exhaust
termination, in spite of the 12-inch vertical offset. See figure
25.
Each 90 ° elbow (including those provided with the furnace)
of any diameter is equivalent to 5 feet (1.52m) of vent pipe
of the same diameter. Two 45 ° elbows are equivalent to
one 90 ° elbow of the same diameter, One 45 ° elbow is
equal to 2,5 feet (,76m) of vent pipe of the same diameter,

In some applications which permit the use of several different sizes of vent pipe, a combination vent pipe may be
used. Contact Lennox' Application Department for assistance in sizing vent pipe in these applications,
NQ TE - The flue collar on all models is sized to accommodate 2" Schedule 40 flue pipe. When vent pipe which is
larger than 2" must be used in an upflow application, a 2"
elbow must be applied at the flue collar in order to properly
transition to the larger diameter flue pipe. This elbow must
be added to the elbow count used to determine acceptable
vent lengths. Assign an equivalent feet value to this elbow
according to the larger size pipe being used. Contact the
Application Department for more information concerning
sizing of vent systems which include multiple pipe sizes.
Use the following steps to correctly size vent pipe diameter,
Refer to Vent Pipe Size Determination
Worksheet on
page 48.
1 - Determine the vent termination and its corresponding
equivalent feet value according to table 5.
2 - Determine the number of 90° elbows required for both
indoor and outdoor (e,g. snow riser) use, Calculate the
corresponding equivalent feet of vent pipe.
3 - Determine the number of 45 ° elbows required for both
indoor and outdoor use, Calculate the corresponding
equivalent feet of vent pipe,
4 - Determine the length of straight pipe required,
5- Add the total equivalent feet calculated in steps 1
through 4 and compare that length to the maximum
values given in table 7 for the proposed vent pipe diameter. If the total equivalent length required exceeds
the maximum equivalent length listed in the appropriate table, evaluate the next larger size pipe,

Exhaust Pipe Offset

I
I
I"il" 12" Min. "_

Upflow Application
Side Wall Termination

Upflow Application
Rooftop Termination

12" Min.
12" Min. -'l_I

I
Iiill

I
_t"4'
I

Horizontal Application
Rooftop Termination

Wall Termination
I Side
orizontal
Application
FIGURE 25

Page 18

A, IMPORTANT

A, WARNING

TABLE 6
MINIMUM VENT PIPE LENGTHS
G51MP
MODEL

MIN. EQUIV.
VENT LENGTH

045,070,
O9O

1 - Measure and cut vent pipe to desired length.
2 - Debur and chamfer end of pipe, removing any ridges

EXAMPLE
5 ft. plus 2 elbows of 2", 2-1/2", 3"
or 4" diameter pipe

110"*

5 ft, plus 2 elbows of 2", 2-1/2", 3" or
4" diameter pipe

15 ft,*

5 ft. plus 2 elbows of 3" or4"
diameter pipe

135"**
*Any approved
length listed.

termination

may be added to the minimum

equivalent

***G51MP-60D-135 must have 3" to 2" reducing ell (supplied) installed directly into unit flue collar.

TABLE 7
MAXIMUM VENT PIPE LENGTHS
(2 PIPE) AND

G51MP
MODEL

ALTITUDE

0-2000
(0-609 m)

2001 -4500
(610-1371
m)

4501-7500
(1372-2286 m)

7501 -10000
(2287-3048

NON-DIRECT

(1 PIPE) APPLICATIONS

MAXIMUM EQUIVALENT
LENGTH FEET

3 - Clean and dry surfaces to be joined,
4 - Test fit joint and mark depth of fitting on outside of
pipe,

**G51MP-48C-110 and G51MP-60C-110 must have 90 ° street ell (supplied) installed directly into unit flue collar.

DIRECT

or rough edges. If end is not chamfered, edge of pipe
may remove cement from fitting socket and result in a
leaking joint,

5 - Uniformly apply liberal coat of PVC primer for PVC or
ABS cleaner for ABS to inside socket surface of fitting
and male end of pipe to depth of fitting socket,
6 - Promptly apply solvent cement to end of pipe and inside socket surface of fitting. Cement should be applied lightly but uniformly to inside of socket, Take care
to keep excess cement out of socket, Apply second
coat to end of pipe.

VENT

2" dia.

2-1/2" dia.

3" dia.

4" dia.

045
070

110
70

135
135

160
160

250
250

090
110"

50
30

100
70

125
125

225
200

135"*

n/a

**'125

180

045
070

110
70

135
135

160
160

250
250

090
110"

50
20

100
70

125
125

225
200

135"*
045

n/a
110

n/a
135

***90
160

180
250

070

135

160

250

090
110"

30
n/a

100
70

125
125

225
200

135"*
045

n/a
110

n/a
135

***90
160

180
250

070
090
110"

70
n/a
n/a

135
100
70

160
125
125

250
225
200

135"*

n/a

***90

180

NOTE - Time is critical at this stage. Do not allow primer to dry before applying cement.
7 - Immediately after applying last coat of cement to pipe,
and while both inside socket surface and end of pipe
are wet with cement, forcefully insert end of pipe into
socket until it bottoms out, Turn PVC pipe 1/4 turn during assembly (but not after pipe is fully inserted) to distribute cement evenly, DO NOT turn ABS or cellular
core pipe,
NOTE - Assembly should be completed within 20 seconds after last application of cement. Hammer blows
should not be used when inserting pipe.
8 - After assembly, wipe excess cement from pipe at end
of fitting socket, A properly made joint will show a bead
around its entire perimeter, Any gaps may indicate a
defective assembly due to insufficient solvent,
9 - Handle joints carefully until completely set,

n/a-- Notallowed.
*G51MP-48C-110 and G51MP-60C-110 must have 90 ° street ell (supplied) installed directly into unit flue collar.
**G51MP-60D-135 must have 3" to 2" reducing ell (supplied) installed directly into unit flue collar.
***90 ° elbows used in configuration of G51MP-60D-135
ited to 3" sweep elbows.

vent, must be lim-

All cementing of joints should be done according to the
specifications outlined in ASTM D 2855.

Page 19

The thickness of construction through which vent pipes
may be installed is 24" (610mm) maximum and 3/4"
(19mm) minimum. If a G51MP furnace replaces a furnace
which was commonly vented with another gas appliance,
the size of the existing vent pipe for that gas appliance must
be checked. Without the heat of the original furnace flue
products, the existing vent pipe is probably oversized for
the single water heater or other appliance. The vent should
be checked for proper draw with the remaining appliance,

1 - Userecommended
pipingmaterialsforexhaustpiping.
2 - Securealljoints,including
dripleg,gas-tight
usingapprovedcement.
Suspendpipingusinghangersata minimum
ofevery
5 feet(1.52m)for schedule40 PVCandevery3
STRAPPING
feet(.91m)forABS-DWV,
(metal,
plastic
or large wire

PVC-DWV, SPR-21 PVC,
and SDR-26 PVC piping.
A suitable
fabricated
or plastic
large wire
3-

ties)

hanger can be
by using metal
strapping or a
tie.

FIGURE 26

In areas where piping penetrates joists or interior
walls, hole must be large enough to allow clearance on
all sides of pipe through center of hole using a hanger.

5 - When furnace is installed in a residence where unit is
shut down for an extended period of time, such as a
vacation home, make provisions for draining condensate collection trap and lines.
Exhaust Piping
NOTE - A 2" diameter street ell is located on the blower
deck of 48C-110 and 60C-110 units. Street eft must be
glued with ABS solvent cement directly into the unit flue
collar. See figure 27. A 3"to 2"reducing ell is located on the
blower deck of the 60D-135 units. In upflow or downflow
applications,
the reducing ell must be glued with ABS solvent cement directly into the unit flue collar.
1 - Choose the appropriate side for venting in upflow or
downflow positions, Exhaust piping exits from the top
of the unit in horizontal air discharge applications.
Glue the field-provided exhaust vent pipe (or provided
street ell or reducing ell in upflow or downflow applications) to the flue collar. All PVC cement joints should
be made according to the specifications outlined in
ASTM D 2855. Refer to pipe and fittings specifications
and gluing procedures,

4 - Secure piping at the point where it exits the outside
wall or roof in order to prevent transmission of vibration to the structure.
TYPICAL

EXHAUST PIPE CONNECTIONS
AND CONDENSATE
TRAP INSTALLATION
IN UPFLOW OR DOWNFLOW DIRECT OR NON-DIRECT VENT APPLICATIONS
(Right-Hand Exit in Upflow Application Shown)
2-1/2",
3", OR
4"

PLUG
[2

PLUG

[_]

2"
TRANSmON

or 090 with 070
G51MP-045,
2-1/2", 3", or 4"
vent pipe

2" LJ
VENT PLUG
(Must be
glued in
place)

2" G51MP-045,
-070 or -090
ONLY

__2"

TRANSmON

3", OR
2-1/2",

PLUG

(use only if4"
pipe is
required)

TRANSmON

CONDENSATE
TRAP
(Must be installed
on same side as
exhaust piping)

_
[_

2 ..... _

* 2" diameter street elbow provided.
** 3" diameter reducing elbow provided.
*** Limit pipe length to 2".

G51MP-110 with
2" vent pipe

G51MP-110 with
2-1/2", 3", OR 4"
vent pipe

FIGURE 27

Page 20

G51MP-135 with
3" OR 4" vent pipe

TYPICAL

EXHAUST PIPE CONNECTIONS
HORIZONTAL DIRECT OR
NON-DIRECT VENT APPLICATIONS
(Horizontal Right-Hand Air Discharge Application Shown)

*Limit pipe length
in
G51MP-110

2-1/2",
3", OR
4"

to 2"
and

- 135 applications.

TRANSiTiON

2"* []

Route piping to outside of structure, Continue with
installation following instructions given in piping termination section.

A. CAUTION

G51MP-36B-045
G51MP-36B-070
G51
MP-36C-090
G51MP-24B-045
G51MP-48C-090
G51MP-60C-090
G51MP-48C-110"
G51MP-60C-110"
G51MP-60D-135*

2 _,

,A CAUTION
DO NOT transition from
smaller
to larger
pipe
size in horizontal runs.

1MP-24B-045
G51MP-36B-045
G51MP-36B-070
G51 MP-36C-090
G51 MP-48C-090
G51 MP-48C-110
G51MP-60C-090
G51MP-60C-110

Intake Piping
The G51MP furnace may be installed in either direct vent
or non-direct vent applications. In non-direct vent applications, when intake air will be drawn into the furnace from the
surrounding space, the indoor air quality must be considered and guidelines listed in Combustion, Dilution and
Ventilation Air section must be followed.
The G51MP unit is designed for either left-side or right-side
air intake connections in either upfiow or downfiow applications. In horizontal applications, air intake must be brought
in through the top. Intake air piping is independent of exhaust piping.

FIGURE 28

Follow the next four steps when installing the unit in Direct
Vent applications,
where combustion air is taken from
outdoors and flue gases are discharged outdoors. The
provided air intake screen must not be used in direct
vent applications.

,&,IMPORTANT

1 - Cement intake piping in slip connector located on the
side of the burner box.

2 - All horizontal runs of exhaust pipe must slope back toward unit. A minimum of 1/4" (6mm) drop for each 12"
(305mm) of horizontal run is mandatory for drainage.
Horizontal runs of exhaust piping must be supported
every 5 feet (1.52m) using hangers.

2 - Use a sheet metal screw to secure the intake pipe to
the connector, if desired. A pilot indentation is provided in the slip connector to assist in locating and
starting the fastener.
3 - Glue the provided 2" plug into the unused air intake
connector on the opposite side of the cabinet.

NOTE - Exhaust piping should be checked carefully to
make sure there are no sags or low spots.

Route piping to outside of structure. Continue with
installation following instructions given in general
guide lines for piping terminations and in intake and

3 - On the opposite side of the cabinet, glue the provided
2" vent plug into the unused flue collar.

exhaust piping terminations for direct vent sections.
Refer to figure 29 for pipe sizes.

Page 21

TYPICAL AIR INTAKE PIPE CONNECTIONS
UPFLOW OR DOWNFLOW DIRECT VENT APPLICATIONS
(Right-Hand Exit in Upflow Application Shown)

3" OR
2-1/2",

4 _

TRANSITION

2-1/2",
3" OR
4'

_]_
2'*_

TRANSITION
2"*X

PLUG
(Must be
glued in
place)

2"*_

....................

G51MP-24B-045
G51MP-36B-045
G51MP-36B-070
G51MP-36C-090
G51MP-48C-090
G51MP-48C-110
G51MP-60C-090
G51MP-60C-110

G51MP-24B-045
G51MP-36B-045
G51MP-36B-070
G51MP-36c-0g0
G51 MP-48C-090
G51MP-60C-090
G51 MP-48C-110"
G51M P-60C-110"

G51MP-24B-045
G51MP-36B-045
G51MP-36B-070
G51 MP-36C-090
G51 MP-48C-090
G51MP-60C-090
G51 MP-48C-110*
G51MP-60C-110*
G51MP-60D-135*

*Limit pipe length to 2"
in G51MP-110 and -135
applications.

FIGURE 29
TYPICAL AIR INTAKE PIPE CONNECTIONS
HORIZONTAL
(Horizontal

*Limit pipe
length to 2"in
G51MP-110
and -135
applications.

DIRECT

Right-Hand

VENT

APPLICATIONS

Air Discharge

Application

G51MP-36B-045
G51MP-24B-045
G51M P-36B-070
G51MP-36C-090
G51MP-48C-090
G51MP-60C-090
G51MP-48C-110"
G51 M P-60C- 110*
G51MP-60D-135*
G51 MP-24B-045
G51MP-36B-045
G51 MP-36C-090
G51MP'36B-070
G51 MP-48C-090
G51MP-60C-090

:_q_

G51MP-48C-110*
G51MP-60C-110"

G51MP-24B-045
G51MP-36B-045
G51MP-36B-070
G51MP-36C-090
G51MP-48C-090
G51MP-48C-110
G51MP-60C-090
G51MP-60C-110

Shown)

Follow the next three steps when installing the unit in NonDirect Vent applications
where combustion air is taken
from indoors and flue gases are discharged outdoors.

__T

TYPICAL
AIR INTAKE PIPE CONNECTIONS
UPFLOW OR HORIZONTAL NON-DIRECT
VENT APPLICATIONS
(Right-Hand Exit in Upflow Application Shown)

TRANSITION

2"*

2-1/2",
.........
3" OR 4"

TRAN_SlTON " t
I

PLUG
(Must be
glued in
place)

2'_

INTAKE
DEBRIS
SCREEN
(Provided)

2" _

NOTE - Debris screen and elbow may be rotated, so that
screen may be positioned to face forward, backward or
downward.

FIGURE 31
FIGURE 30
Page 22

TYPICAL AIR INTAKE PIPE CONNECTIONS
DOWNFLOW NON-DIRECT VENT APPLICATIONS
(Right-Hand Exit in Downfiow Applications Shown)

2" SWEEP
ELL

INTAKE
DEBRIS
SCREEN
(Provided)

6 in. Max.
PLUG
_[_pqU
st be
ed tn
lace)

PLUG
(gl_ust be
ed t

qaee

2_
INTAKE DEBRIS
SCREEN
(Provided)
Downflow Additive Flloor Base

Downflow
Evaporator
Coil
O

NOTE

- Debris

screen

may be positioned

screen

and sweep

ell may be rotated,

to face forward,

backward

so that

or to the side.

FIGURE 32
1 - Use field-provided materials and the factory-provided
air intake screen to route the intake piping as shown in
figures 31 and 32, Maintain a minimum clearance of 3"
(76mm) around the air intake opening. The air intake
opening (with the protective screen) should always be
directed either downward or straight out. Use 2" pipe
and fittings only and make sure that the air intake does
not extend more than 6" beyond the G51MP cabinet,
The air intake connector must not be located near

Testing for Proper Venting and Sufficient
Air
(Non-Direct Vent Applications

Combustion
Only)

WARNING

the floor. To avoid this complication
in downflow
applications
which do not include a downflow
evaporator coil, the intake air routing should be modified as shown in figure 32,
2 - Use a sheet metal screw to secure the intake pipe to
the connector, if desired, A pilot indentation is provided in the slip connector to assist in locating and
starting the fastener,
3 - Glue the provided 2" plug into the unused air intake
connector on the opposite side of the cabinet,

After the G51MP gas furnace has been started, the following test should be conducted to ensure proper venting and
sufficient combustion air has been provided to the G51MP,
as well as to other gas-fired appliances which are separately vented, The test should be conducted while all appliances (both in operation and those not in operation) are
connected to the venting system being tested, If the venting system has been installed improperly, or if provisions
have not been made for sufficient amounts of combustion
air, corrections must be made as outlined in the previous
section,

Page 23

1 - Sealanyunusedopeningsintheventingsystem.
2 - Visuallyinspect
theventingsystemforpropersizeand
horizontal
pitch.Determine
thereis noblockage
orrestriction,leakage,corrosion,or other deficiencies
whichcouldcauseanunsafecondition.
3 - Totheextentthatitispractical,
closeallbuildingdoors
andwindowsandall doorsbetweenthe spacein
whichtheappliances
connected
totheventingsystem
arelocatedandotherspacesofthebuilding.
4 - Closefireplacedampers.
5 - Turnon clothesdryersandanyappliances
notconnectedto the ventingsystem.Turnon anyexhaust
fans,suchasrangehoodsandbathroom
exhausts,
so
theywilloperateatmaximum
speed.Donotoperatea
summerexhaustfan.
6 - Followthelightinginstruction
to placetheappliance
beinginspectedintooperation.
Adjustthermostat
so
appliance
willoperatecontinuously.
7 - Usetheflameofmatchor candletotestforspillageof
fluegasesatthedrafthoodreliefopeningafter5 minutesofmainburneroperation.
8- If improperventingis observedduringany of the
abovetests,theventingsystemmustbecorrected
or
sufficientcombustion/make-up
airmustbeprovided.
Theventingsystemshouldbe re-sizedtoapproach
the minimumsize as determinedby usingthe appropriatetablesinappendix
G inthecurrentstandards
oftheNational
FuelGasCodeANSI-Z223.1/NPFA
54
in the U.S.A.,andthe appropriateNaturalGasand
Propaneappliances
ventingsizingtablesin thecurrentstandardoftheCSA-B149
NaturalGasandPropaneInstallation
Codesin Canada.
9 - Afterdetermining
thateachappliance
remaining
connectedtothecommonventingsystemproperlyvents
whentestedas indicated
instep3,returndoors,windows,exhaustfans,fireplacedampersandanyother
gas-burning
applianceto theirpreviousconditionof
use.
GeneralGuidelinesfor VentTerminationsfor Non-DirectVentInstallations.
In Non-Direct
Ventapplications,
combustion
air is taken
fromindoorsandthefluegasesaredischarged
totheoutdoors.TheG51MPisthenclassified
asa non-direct
vent,
CategoryIVgasfurnace.InNon-Direct
Ventapplications,
theventtermination
is limitedbylocalbuilding
codes.Inthe
absenceof localcodes,refertothecurrentNationalFuel
GasCodeANSIZ223-1/NFPA
54 in U.S.A.,andcurrent
CSA-B149
NaturalGasandPropaneInstallation
Codesin
Canadafordetails.

Positiontermination
endaccording
to locationgiveninfigure33. Inaddition,positiontermination
endso it is free
fromanyobstructions
andabovethe levelof snowaccumulation(whereapplicable).
Thetermination
shouldbeat
least12inches(305mm)fromanyopeningthroughwhich
flueproductscouldenterthebuilding.
At vent termination,care must be taken to maintain
protectivecoatingsover buildingmaterials(prolonged
exposureto exhaustcondensate
candestroyprotective
coatings).
It is recommended
thattheexhaust
outletnotbe
locatedwithin6 feet(1.8m)of a condensing
unitbecause
thecondensate
candamagethepaintedcoating.
NOTE - If winter design temperature is below 32°F (0°C),
exhaust piping should be insulated with 1/2" (13mm), Armaflex or equivalent when run through unheated space.
Do not leave any surface area of exhaust pipe open to outside air, exterior exhaust pipe should be insulated with 1/2"
(13mm) Armaflex or equivalent. In extreme cold climate
areas, 3/4" (f9mm) Armaflex or equivalent may be necessary. Insulation on outside runs of exhaust pipe must be
painted or wrapped to protect insulation from deterioration.
Exhaust pipe insulation may not be necessary in some
specific applications.
NOTE - During extremely cold temperatures, below
approximately 20°F (6.7°C), units with long runs of vent
pipe through unconditioned space, even when insulated,
may form ice in the exhaust termination that prevents the
unit from operating properly. Longer run times of at least 5
minutes will alleviate most icing problems. Also, a heating
cable may be installed on exhaust piping and termination to
prevent freeze-ups. Heating cable instaflation kit is available from Lennox. See Condensate Piping section for part
numbers.

Page 24

A IMPORTANT

,&IMPORTANT

VENT TERMINATION
CLEARANCES
FOR INSTALLATIONS
IN THE USA AND CANADA*

[]

- G51MP VENT TERMINATION

- AIR INLET OF OTHER APPLIANCE

!
A - Clearance above grade - 12 in, (305mm)

minimum,

B - Clearance to window or door that may be opened for vent installations
in USA - 12 in. (305mm) minimum,
for vent installations
in Canada - 12 in, (305ram) minimum for appliances _ 100,000 Btuh (30 kW);
36 in. (0.9m) minimum for appliances > 100,000 Btuh (30
kW).
C - Do notposition

terminations

directly underroofeaves.

D - Clearance to electric meters, gas meters, regulators, and
relief equipment for vent installations in USA - 48 in (1219mm) minimum,
for vent installations
in Canada - see current edition of
CSA B149 Code.

E - Clearance to non-mechanical air supply inlet or outlet
for vent installations
in USA - 48 in. (1219mm) minimum
horizontal and below, 12 in. (305ram) minimum above.
for vent installations
in Canada - 12 in. (305mm) minimum for appliances _ 100,000 Btuh (30 kW);
36 in. (0.9m) minimum for appliances > 100,000 Btuh (30
kW).
F - Clearance to mechanical air supply inlet -for vent installations
in USA - 36 in. minimum (914mm}.
G - Clearance to mechanical air supply inlet -for vent installations
in Canada - 72 in. (1829mm)
mum.

H - Do notpoint terminations into recessed areas such as window wells, stairwells or alcoves.
J - Do not position terminations

directly above a walkway.

* Note (I) Dimensions are from the current edition of The National Fuel Gas Code - ANSI-Z223.1/NFPA
54 for USA installations. In Canada, refer to current edition of CSA B149 installation codes. Local codes or regulations may require different clearances.
(11)In Non-Direct Vent installations, combustion air is taken from indoors and the flue gases are discharged to the outdoors.

FIGURE 33

Page 25

mini-

Details of Intake and Exhaust Piping Terminations for
Direct Vent Installations
NOTE - In Direct Vent installations, combustion air is taken
from outdoors and flue gases are discharged to outdoors.
Intake and exhaust pipes may be routed either horizontally
through an outside wall or vertically through the roof. In attic or closet installations, vertical termination through the
roof is preferred, Figures 34 through 42 show typical terminations.
1 - Exhaust and intake exits must be in same pressure
zone, Do not exit one through the roof and one on the
side. Also, do not exit the intake on one side and the
exhaust on another side of the house or structure.

112 (13) ARMAFLEX
INSULATION IN
UNCONDITIONED
SPACE

iiiiiiiiir...li-

FIELD-

G51MP
MODEL

Exhaust Pipe Size

045 and 070

2", 2-1/2", 3" or 4"

090

2", 2-1/2", 3" or4"

110
135

2", 2-1/2", 3" or4"
3" or4"

2"*
2"*

*Approved 3" concentric termination

Termination

Pipe Size

1-1/2"

kit terminates with 2-5/8" ID pipe.

112" (13)
' ARMAFLEX
INSULATION
--i_

...........--._

t--I-

["1"

6 (152)
MAXIMUM

SIZE
TERMINATION

li-

TABLE 8.
PIPE PER
2 (51) PVC
COUPLING

OUTSIDE

2 - intake and exhaust pipes should be placed as close
together as possible at termination end (refer to illustrations). Maximum separation is 3" (76mm) on roof
terminations and 6" (152mm) on side wall terminations.
3 - if necessary, install a field-provided reducer to adapt
larger vent pipe size to termination pipe size.
4 - On roof terminations, the intake piping should terminate straight down using two 90 ° elbows (See figure
34).
5 - Exhaust piping must terminate straight out or up as
shown, In rooftop applications, a reducer may be required on the exhaust piping at the point where it exits
the structure to improve the velocity of exhaust away
from the intake piping. See table 8.
NOTE - Care must be taken to avoid recirculation of
exhaust back into intake pipe.
TABLE 8
EXHAUST PIPE TERMINATION SIZE REDUCTION

\
_

PROVIDED
REDUCER MAY
BE REQUIRED
TO ADAPT
LARGER VENT
PIPE SIZE TO
TERMINATION

12 (305) MAX.

J
:

WALL

Inches (mm)

8 (203)

MINIMUM

TOP VIEWWALL

RING KIT

(15J74)

FIGURE 35
6 - On field supplied terminations for side wall exits, exhaust piping should extend a maximum of 12 inches
(305mm) beyond the outside wall. Intake piping
should be as short as possible, See figure 35,
7 - On field supplied terminations, a minimum separation
distance between the end of the exhaust pipe and the
end of the intake pipe is 8 inches (203mm),
8 - If intake and exhaust piping must be run up a side wall
to position above snow accumulation or other obstructions, piping must be supported every 3 ft. (.9m) as
shown in figure 26. Refer to figure 38 for proper piping
method. In addition, WTK wall termination kit must be
extended for use in this application. See figure 41.
When exhaust and intake piping must be run up an
outside wall, the exhaust piping must be terminated
with pipe sized per table 8. The intake piping may be
equipped with a 90 ° elbow turndown. Using turndown
will add 5 feet (1,5m) to the equivalent length of the
pipe.
9 - Based on the recommendation of the manufacturer, a

Inches(ram)

3(76) MAX.
_

SIZE TERMINATION
PIPE

PER

TABLE

multiple furnace installation may use a group of up to
four termination kits WTK assembled together horizontally, as shown in figure 40,

UNCONDITIONED
ATTIC SPACE

8" (203) MIN

112" (13) FOAM
INSULATION IN
UNCONDITIONED
SPACE

12" (305) ABOVE
AVERAGE SNOW
ACCUMULATION

3" (76) OR
2" (51) PVC
PROVIDESUPPORT
FORINTAKE
AND
EXHAUST LINES

DIRECT VENT ROOF TERMINATION
(15F75 or 44J41)

KIT

FIGURE 34

Page 26

EXHAUST
TERMINATION

INTAKE

EXHAUST

12" (305) ABOVE
AVERAGE SNOW
ACCUMULATION

INTAKE
VENT

Inches (mm)

__'_

Front View

1/2" (13) Foam Insulation
in Unconditioned
Space

TERM____

I I

]

Side View

FIELD-PROVIDED

[',_

EXHAUST

REDUCER MAY BE REQUIRED
TO ADAPT LARGER VENT
PIPE SIZE TO TERMINATION

EXHAUST

VENT

REDUCER MAY
BE REQUIRED
TO ADAPT
LARGER VENT
PIPE SIZE TO
TERM
NAT ON
PROVIDED
FIELD-

INTAKE

DIRECT VENT CONCENTRIC ROOFTOP TERMINATION
(71 M80, 69M29 or 60L46)

Inches

FIGURE 36

(ram)

OUTSIDE

DIRECT

VENT

(22G44,

WALL

44J40,

TERMINATION
30G28

VENT
WALL

KIT

or 81J20)

FIGURE 39
Inches (mm)

INTAKE
TERMINATION
TERMINATION
,°

,.)°

VENT

,NTAKEvENT
°

12"E_HAUST
(305) Min.
above grade.

_f
FIELD-PROVIDED
REDUCER MAY
BE REQUIRED TO
ADAPT LARGER
VENT PIPE SIZE
TO TERMINATION

18" MAX.

(4s7/ _

•

DIRECT VENT CONCENTRIC

Front View

EXHAUST

WALL TERMINATION

(71 M80, 69M29 or 60L46)

,NTAKE

Inches (ram)

VENT

FIGURE 37
_,_
Inches(ram)

12" (305) MAX. for 2"

SIZE
TERMINATION
PIPE PER
TABLE 8.

FIELD-PROVIDED
REDUCER MAY
BE REQUIRED TO
ADAPT LARGER
VENT PIPE SIZE
TO TERMINATION

12" (305) ABOVE
AVERAGE SNOW
ACCUMULATION

t/2 'I (13) FOAM
INSULATION IN
UNCONDITIONED
SPACE

DIRECT

FIGURE 40

PROVIDE SUPPORT
FOR INTAKE AND
EXHAUST LINES EVERY
36" (914)

VENT

1/2" (13) FOAM
INSULATION

SIDE
WALL

VIEW
RING

TERMINATION

(15F74)
See venting

table 7 for maximum

venting

lengths

Side View

OPTIONAL VENT TERMINATION FOR MULTIPLE UNIT
INSTALLATION OF DIRECT VENT WALL TERMINATION KIT
(22G44, 44J40, 30G28 or 81J20)

UNCONDITIONED
SPACE
OUTSIDE WALL

VENT

with this arrangement.

FIGURE 38

Page 27

12" (305) MAX. for2"

(51)

20" (508) MAX. for3"

(L)6) I

Inches

(305)
-Iq

//
INTAKE
AIR

/1[_[_1_

8"(203)

r I_1 "

x., ust

I"=-

1,7

,f l

EXHAUST
AIR

12-(305)
5"
(127)

Side View

GRADE

1/2" (13)
FOAM
INSULATION

INTAKE
AIR

Minimum

i i iI
J! il

COVER EXHAUST
VENT WITH

12"

(ram)

Iw'-,

,f l

WALL TERMINATION

,f l

12" MIN.
(305)
Above Grade

GRADE

i
i

,f l

> f

Front View

DIRECT VENT TERMINATION
KIT (22G44, 44J40, 30G28 or 81J20) EXTENDED VENT FOR GRADE CLEARANCE

FIGURE 41
G51MP DIRECT VENT APPLICATION
USING EXISTING CHIMNEY

Inches(rnrn)

ST_IGNT-COTOR

ANGLE_CUT

OF ROOF

DIRECTION

SLOPE

8
(203rr m

12
305rr m)

TERMINATION

PIPE

PER

TABLE

12" (305ram)
ABOVE AVE.
SNOW
ACCUMULATIOI

7
EXHAUST

SIZE

VENT

112" (13ram)
WEATHERPROOF

INSULATION

SHOULDER
OF FITTINGS
PROVIDE SUPPORT
OF PIPE ON TOP PLATE

_NTAKE P_PE
fNSULATfON (optioPal)
SHEET
METAL TOP
PLATE

3" (76)

2" (51) PVC

ALTERNATE
INTAKE PIPE

UNCONDITIONED
ATTIC
SPACE

PROVIDE SUPPORT
FOR EXHAUST LINES

MINIMUM
12"
(305mm) ABOVE
ROOF

03rrlm)

EXTERIOR

NON-DIRECT
*SIZE TERMINATION
PIPE PER TABLE 8.

P%,7o_
oF

VENT ROOF TERMINATION
(15F75 or 44J41)

KIT

FIGURE 43

NOTE - Do not discharge exhaust gases directly into any chimney or vent stack. If vertical discharge through an existing unused chimney or stack is required, insert piping
inside chimney until the pipe open end is above top of chimney and terminate
as illustrated.

In any exterior

portion

of chimney,

the exhaust

vent

must

be insulated.

FIGURE 42
Details of Exhaust Piping Terminations for Non-Direct

12" (305) Max. for 2" (51)

Vent Applications
Exhaust pipes may be routed either horizontally through an
outside wall or vertically through the roof. In attic or closet
installations, vertical termination through the roof is preferred. Figures 43 through 46 show typical terminations.
1 - Exhaust piping must terminate straight out or up as

1/2" (13) ARMAFLEX
INSULATION IN
UNCONDITIONED
SPACE

1/2"

(13)

I /ARMAFLEX
FIELD-PROVIDED
"_
REDUCER MAY r .........
BE REQUIRED TO
ADAPT LARGER
VENT PiPE SIZE
TO TERMINATION

shown. The termination pipe must be sized as listed in
table &The specified pipe size ensures proper velocity required to move the exhaust gases away from the
building.
2 - On field supplied terminations for side wall exits, exhaust piping should extend a maximum of 12 inches
(305mm) beyond the outside wall. See figure 44.

,,_'_

I--,--rll i
=k_

Inches

PVC
SIZE

(mm)

REDUCER
TERMINATION

PiPE PER TABLE

NON-DIRECT

TOP VIEW
VENT WALL RING KIT
(15F74)

FIGURE 44

Page 28

INSULATION

3 - If exhaustpipingmustberunupa sidewalltoposition
abovesnowaccumulation
or otherobstructions,
pipingmustbesupported
every3feet(.9m)asshownin
figure26,Refertofigure45forproperpipingmethod.
Whenexhaustpipingmustberunupanoutsidewall,
anyreduction
inexhaustpipesizemustbedoneafter
thefinalelbow,
Inches(ram)

12" (305) Max. for2"

(51)

sate trap should extend below the unit. A 5-1/2" service
clearance is required for the condensate trap. Refer to figure for condensate trap locations.
CONDENSATE TRAP LOCATIONS
(Unit shown in upflow position)
Horizontal
left and
optional
downf!ow

_--

_--_]
LLJ

Horizontal
right and
optional
downf!ow

[--_
L_

_
__

Optional
upflow

UNCONDITIONED
SPACE

OUTSIDE

WALL

SIZE TERMINATION
PIPE PER
TABLE 8.

PROVIDE SUPPORT
FOR EXHAUST LINES
EVERY 30" (914)

Optional
upflow

12" (305) ABOVE
AVERAGE SNOW
ACCUMULATION

FIELD-PROVIDED
REDUCER MAY BE
REQUIRED TO
ADAPT LARGER
VENT PIPE SIZE TO
TERMINATION
1/2" (13) FOAM
INSULATION

IN
INSULATION

NOTE - In upflow applications where side return
air filter is installed on same side as the conden-

SIDE VIEW
VENT WALL RING TERMINATION
(15F74)

sate trap, filter rack must be installed beyond
condensate trap to avoid interference.

UNCONDITIONED

1/2 l' (13) FOAM

SPACE

NON-DIRECT

FIGURE 45

FIGURE 47
_

G51MP NON-DIRECT VENT APPLICATION
USING EXISTING CHIMNEY
SIZE

TERMINATION

PIPE

PER

TABLE

ANGLE-CUT

IN DIRECTION

OF ROOF SLOPE

3 8
(76ram
203rnm)
MINIMUM
12"
(305ram) ABOVE
AVERAGE
SNOW
ACCUMULATION

NOTE - The condensate trap is factory-shipped with
two rubber O-rings and two rubber clean-out caps
installed. Check to make sure that these items are in

STRAIGHT-CUT OR
8.

place before installing the trap assembly.

1/2" (13ram)
WEATHERPROOF
INSULATION
EXHAUST
VENT

SHOULDER
OF FITTINGS
PROVIDE SUPPORT
OF PIPE ON TOP PLATE
METAL TOP
PLATE
SHEET

(76mr_

INSOLATE
TO FORM

SEAL

203rr m)
_

Determine which side condensate piping will exit the
unit. Remove plugs from the condensate collar at the
appropriate location on the side of the unit.

EXTERIOR

Install condensate trap onto the condensate collar.
Use provided HI/LO screws to secure two upper
flanges of the trap to the collar, Use provided sheet
metal screw to secure bottom trap flange to side of
unit, See figure 48,
NOTE - In upflow and downflow applications, condensate trap must be installed on the same side as
exhaust piping.

CAUTION

%T_O_OF

NOTE - Do not discharge exhaust gases directly into any chimney or vent stack. If vertica] discharge through an existing unused chimney or stack is required,
insert piping
inside chimney until the pipe open end is above top of chimney and terminate
as illustrated. In any exterior portion of chimney,
the exhaust vent must be insu]ated.

FIGURE 46
Condensate Piping
This unit is designed for either right- or left-side exit of condensate piping in either upfiow or downfiow applications;
however, it must be installed on the same side of the unit as
the exhaust piping, In horizontal applications, the conden-

Page 29

3 - Glue the field-provided coupling or pipe to the trap.
Install a tee and vent pipe near the trap.
NOTE - The condensate trap drain stubs (both sides)
have an outer diameter which will accept a standard
3/4" PVC coupling. The inner diameter of each stub
will accept standard 1/2" diameter PVC pipe.

NOTE - Vinyl tubing may be used for condensate
drain. Tubing must be 1-1/4" OD X 1" ID and should be
attached to the drain stubs on the trap using a hose
clamp.
4 - Glue the field-provided drain line to the tee. Route the
drain line to an open drain, As an alternate, clear vinyl
tubing may be used to drain condensate away from
the trap, Secure the vinyl tubing to the drain stubs on
the trap using a hose clamp, Do not overtighten the
hose clamp,
Condensate line must be sloped downward away from
condensate trap to drain, If drain level is above condensate trap, condensate pump must be used, Condensate drain line should be routed within the conditioned space to avoid freezing of condensate and
blockage of drain line, If this is not possible, a heat
cable kit may be used on the condensate trap and line.
Heating cable kit is available from Lennox in various
lengths; 6 ft, (1.8m) - kit no. 26K68; 24 ft. (7.3m) - kit
no, 26K69; and 50 ft, (15,2m) - kit no, 26K70,

-&CAUTION

_ WARNING
1 - Gas piping may be routed into the unit through either
the left- or right-hand side. Supply piping enters into
the gas valve from the side of the valve as shown in
figure 51 or 51.

AIMPORTANT

CAUTION
5 - If unit will be started immediately upon completion of
installation, prime trap per procedure outlined in Unit
Start-Up section.
6 - Glue the provided cap onto the unused condensate
drain line stub.
CONDENSATE

O-RINGS

ASSEMBLY

HI/LO SCREWS
(DO NOT use power
driver. Hand-tighten
using screw driver.)

/VENT

NIPPLE

_TEE
CAP

NIPPLE

COUPLING
_CLEAN-OUT

ACCESS
(both sides)

CONDENSATE

2 - When connecting gas supply, factors such as length of
run, number of fittings and furnace rating must be considered to avoid excessive pressure drop. Table 9 lists
recommended pipe sizes for typical applications.
NOTE - Use two wrenches when connecting gas piping to avoid transferring torque to the manifold.
3 - Gas piping must not run in or through air ducts, clothes
chutes, chimneys or gas vents, dumb waiters or elevator shafts. Center gas line through piping hole. Gas
line should not touch side of unit. See figure 51 or 51.
4 - Piping should be sloped 1/4 inch per 15 feet (6mm per
5.6m) upward toward the gas meter from the furnace.
The piping must be supported at proper intervals, every 8 to 10 feet (2.44 to 3.05m), using suitable hangers
or straps. Install a drip leg in vertical pipe runs to serve
as a trap for sediment or condensate.
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 58 and 60.
6 - In some localities, codes may require installation of a
manual main shut-off valve and union (furnished by installer) external to the unit. Union must be of the
ground joint type.

klMPORTANT

TRAP

SCREW

FIGURE 48

Page 30

MANUAL MAIN SHUT-OFF
VALVE WILL NOT HOLD

XklMPORTANT

FURNACE

ISOLATE
GAS VALVE

&WARNING

FIGURE 49
Leak Check
After gas piping is completed, carefully check all piping
connections (factory- and field-installed) for gas leaks, Use
a leak detecting solution or other preferred means,
The furnace must be isolated from the gas supply system
by closing its individual manual shut-off valve during any
pressure testing of the gas supply system at pressures less
than or equal to 1/2 psig (3.48 kPa, 14 inches w.c.).
Upflow Application
Left Side

AUTOMATIC
GAS VALVE

Piping

Upflow Application
Right Side Piping
(Alternate)

(withmanual

(Standard)

shut-off valve)

MANUAL
MAIN SHUT-OFF
VALVE

MANUAL
MAIN SHUT-OFF

VALVE

GROUND
JOINT
UNION

JOINT
UNION
DRIP

,t
DRIP LEG

FIELD
PROVIDED
AND INSTALLED

FIGURE 50

Page 31

LEG

In LP/propane applications
using a Honeywell
VR8205 gas valve, a 4" BIP nipple must be installed
to accommodate
the low inlet pressure switch.

Horizontal Applications
Possible Gas Piping Configerations
MANUAL
MAIN SHUT-OFF
VALVE

MANUAL
MAIN SHUT-OFF
VALVE

Horizontal Application
Left-Side Air Discharge

J
GROUND
JOINT
UNION

DRIP LEG

•

Horizontal Application
Right-Side Air Discharge

-q

LUlII

MANUAL
MAIN SHUT-OFF
VALVE
(With 1/8 in. NPT
Plugged Tap
Shown)

_31 II
_'-J 2-"

JOINT
UNION

In LP/propane
appfications
using
a
Honeywell
VR8205
gas valve, a 4" BIP
nipple
must be installed
to accommodate
the low inlet pressure
switch.

DRIP LEG

FIGURE 51
TABLE 9
GAS PIPE CAPACITY - FTZ/HR (kL/HR)
Nominal
Iron Pipe Size
-Inches(ram)

Internal
Diameter
-Inches(ram)

Length
10

(3.048)

(6.096)

(9.144)

40
(12.192)

of Pipe-Feet(m)

50
(15.240)

60
(18.288)

70
(21.336)

1/4
(6.35)
3/8
(9.53)

,364
(9.246)

43
(1.13)

29
(.82)

24
(.66)

20
(.57)

18
(.51)

16
(.45)

15
(.42)

.493
(12.522)

95
(2.69)

65
(1.64)

52
(1.47)

45
(1.27)

40
(1.13)

36
(1.02)

1/2
(12.7)

.622
(17.799)

175
(4.96)

120
(3.40)

97
(2.75)

82
(2.32)

73
(2.07)

3/4
(19.05)

.824
(20.930)

360
(10.19)

250
(7.06)

200
(5.66)

170
(4.61)

1
(25.4)

1.049
(26.645)

680
(19.25)

465
(13.17)

375
(10.62)

1-1/4
(31.75)

1,380
(35.052)

1400
(39.64)

950
(26.90)

1-1/2
(38.1)

1.610
(40.694)

2100
(59.46)

2
(50.8)

2,067
(52.502)

2-1/2
(63.5)

8O
(24.384)

9O
(27.432)

100
(30.480)

33
(.73)

14
(.40)
31
(.88)

13
(.37)
29
(.82)

12
(.34)
27
(.76)

66
(1.67)

61
(1.73)

57
(1.61)

53
(1.50)

50
(1.42)

151
(4.26)

138
(3.91)

125
(3.54)

118
(3.34)

110
(3.11)

103
(2.92)

320
(9.06)

265
(6.07)

260
(7.36)

240
(6.80)

22O
(6.23)

205
(5.80)

195
(5.52)

770
(21.60)

660
(16.69)

580
(16.42)

530
(15.01)

490
(13.67)

46O
(13.03)

430
(12.18)

400
(11.33)

460
(41.34)

1180
(33.41)

990
(26.03)

900
(25.46)

810
(22.94)

750
(21.24)

69O
(19.54)

650
(18.41)

620
(17.56)

3950
(111.65)

2750
(77.67)

2200
(62.30)

1900
(53.60)

1680
(47.57)

1520
(43.04)

1400
(39.64)

1300
(36.81)

1220
(34.55)

1150
(32.56)

2,469
(67.713)

6300
(176.39)

4350
(123.17)

3520
(99.67)

3000
(64.95)

2650
(75.04)

2400
(67.96)

2250
(63.71)

2050
(58.05)

1950
(55.22)

1850
(52.38)

3
(76.2)

3,066
(77.927)

11000
(311.48)

7700
(216.03)

6250
(176.98)

5300
(150.07)

4750
(134.50)

4300
(121.76)

3900
(110.43)

3700
(104.77)

3450
(97.69)

3250
(92.03)

4
(101.6)

4.026
(102.260)

23000
(651.27)

15800
(447.39)

12800
(362.44)

10900
(306.64)

9700
(274.67)

6600
(249.18)

6100
(229.36)

7500
(212.37)

7200
(203.88)

6700
(189.72)

NO TE - Capacity given in cubic feet of gas per hour (kilo liters of gas per hour) and based on O.60 specific gravity gas.

Page 32

The unit is equipped with a field make-up box. The makeup 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, the excess wire must be pulled into the blower
compartment. Secure the excess wire to the existing harn-

ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures

ACAUTION

ess to protect it from damage.
Refer to figure 55 for field wiring and figure 57 for schematic
wiring diagram and troubleshooting.
1 - Select circuit protection and wire size according to the
unit nameplate. The power supply wiring must meet
Class I restrictions.
2 - Holes are on both sides of the furnace cabinet to facilitate wiring.
3 - Install a separate disconnect switch (protected by either fuse or circuit breaker) near the furnace so that
power can be turned off for servicing.

INTERIOR MAKE-UP BOX INSTALLATION
MAKE-UP
BOX

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.
5-

ing diagram shown in figure 55. Use 18-gauge wire or
larger that is suitable for Class II rating for thermostat
connections.

Right Side

_
J

8
FIGURE 52
INTERIOR MAKE-UP BOX INSTALLATION
Left side

Complete the wiring connections to the equipment.
Use the provided unit wiring diagram and the field wir-

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) for the
USA and current Canadian Electric Code part 1 (CSA
standard C22.1) for Canada. A green ground wire is
provided in the field make-up box.
NOTE - The G51MP furnace contains electronic components that are polarity sensitive. Make sure that the
furnace is wired correctly and is properly grounded.

BOX

7 - One line voltage "EAC" accessory terminal is provided
on the furnace control board. Any electronic air cleaner
rated up to one amp can be connected to this terminal
with the neutral leg d the circuit being connected to the
any d the "NEUTRAL" terminals. See figure 56 for control board configuration. This terminal is energized
whenever the blower is operating.
8 - One line voltage "HUM" accessory terminal is provided
on the furnace control board. Any humidifier rated up
to one amp can be connected to this terminal with the
neutral leg of the circuit being connected to any of the
"NEUTRAL" terminals. See figure 56 for control board
configuration. This terminal is energized in the heating
mode whenever the combustion air inducer is operating.

FIGURE 53

Page 33

of the circuit being connected to the "C" terminal of the
thermostat terminal block, which is located on the control board.

G51MP and CONDENSING UNIT
THERMOSTAT DESIGNATIONS
(Refer to specific thermostat and outdoor unit.)

Thermostat

G51MP
Furnace

10-Install the room thermostat according to the instructions provided with the thermostat. See figure 54 for
thermostat designations. If the furnace is being
matched with a heat pump, refer to the FM21 installation instruction.

Condensing
Unit

'@t POWER
@
®t
HEAT @
_-_t
_--_t

CONDENSING

COOLING

1 - When the thermostat is set to "FAN ON," the indoor
blower will run continuously on the continuous low
speed (FAN) when there is no cooling or heating demand.

INDooRBLoWER
I_\

Indoor Blower Speeds

UNIT

CONDENSING
UNIT
COMMON

COMMON

FIGURE 54

2 - When the G51MP is running in the heating mode, the
indoor blower will run on the heating speed.

9 - One 24 volt "24V HUM" terminal is provided on the furnace control board. Any humidifier rated up to 0.5 amp
can be connected to this terminal with the common leg

3 - When there is a cooling demand, the indoor blower will
run on the cooling speed.

TYPICAL G51MP FIELD WIRING DIAGRAM
120V ACC
OR
K45 ECON
(IF USED)

547

S#7

01--I0

FLAME
SWITCH
ROLLOUT

FLAME R
--_I_sENS0

£10
PRIMARY
i
LIMIT

000

BURNERS

GAS

Oav
O_v/_

SWITCH
IGNITERRJLR_J FLAME
ROLLOU'
JI59
F:_Pi59
/ £J N

....

LINE VOLTAGE FIELD
INSTALLED
CLASS
II VOLTAGE
FIELD WIRING

-,,m--DENOTES
N
LI_

"i
_ i
c,_

LOW GAS
HONEYWELL
f"_.GAS
VALVE

....( XDB)

sB_y
Hu_
/'_

.....

D-_
) GIG
\zOyCOMBUSTION
_PROVING

{::::3
-;_RE(ALTERNATE

INDUCER
AIR
SWITCH

MOTOR

sv,

TRANSFORMER
INTERLOCK

BLOWER
A92
IGNITION

SI
ROOM THERMOSTAT

F@@@@--01
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(_
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S21
SECONDARY
GAS LIMIT

CONTROL

--m

IS REPLACED, IT
LIKE SIZE,
AND TERMINATION.

IMPORTANTTO PREVENT
MOTOR BURNOUT,NEVER
CONNECT
MORE THAN ONE MOTOR LEAD
TO ANY ONE CONNECTION

./2X PARK TERMINALS
TERMINALS.ALL
MUST BE WIRED

ARE UNPOWERED
UNUSED
MOTOR LEADS
TO A PARK TERMINAL.

ODD _'- Z_
z_DO
CIRCUIT
BREAKER
PI3S
JI3S

r-r-t

@
S2 I
SECONDARY
GAS LIMIT

LL -

IF ANY WIRE IN THIS APPLIANCE
MUST BE REPLACED
WITH WIRE OF
RATING,
INSULATION
THICKNESS,

,,_
SIB (D-i
r
COMBUSTION
AIR".,/O j
PROVING SWITCh

COMPONENTS

WARNINGELECTRIC
SHOCK HAZARD,CAN
CAUSE INJURY
OR DEATH.UNIT
MUST BE GROUNDED
IN ACCORDANCE
WITH NATIONAL
AND LOCAL CODES.

IHITE-RODGER_
GAS VALVE

[_ij8€

COMBUSTION"--IA_"=;'IR
_P84

OPTIONAL

CAP 'ITOR
MOTOR

OUTDOOR
UNIT

FIGURE 55

Page 34

NOT USE RED (LOW SPEED)
LEAD FOR HEATING.
LEAVE ON
TERMINAL
FOR GSIMP-48C-IIO
-36C-090
UNITS

Z_USE

COPPER

CONDUCTORS

MOTOR
PARK
AND

ONLY.

,/_24V
HUM IS A I/4" FEMALE
QUICK
CONNECT
TERMINAL
A
=/-_S145
IS USED WITH HONEYWELL
GAS
VALVE WHEN APPLIED
IN LP GAS UNIT

SURELIGHI'ClNTEGRATED
CONTROL
BOARD
TERMINAL
COOL
HEAT
PARK
FAN
EAC
XFMR
LINE
HUM
5 Terminals
FS
24V HUM

1/4" FEMALE
QUICK
CONNECT

DESIGNATIONS

Blower - Cooling Speed (120VAC)
Blower- Heating Speed (120VAC)
Unused Blower (Not energized)
Continuous Low Blower Speed
Accessory Terminal (120VAC)
Transformer (120VAC)
Input (120VAC)
Heat Only Accessory (120VAC)
120 Volt Neutral
Flame Sensor
Heat Only Accessory (24VAC)

Sl DIP SWITCHES
HEAT OFF DELAY
I
2
SEC
OFF
OFF
60
OFF
ON
90 *
OH
OFF
120
ON
ON
180
COOL

OFF

2 *

•Factory

FIGURE 56

Page 35

OFF DELAY

settin_

SEC

TYPICAL

WIRING

DIAGRAM
BLOWI;R SPEED CHART
FACTORY CONNECTED SPEED TAP.c

120V ACC
OR
K¢5 ECON
(IF USED)

Ol-IO
FLAME ROLLDUT
SWITCH

L
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G51MP

UNIT

000

BURNERS

_
FLAME
_.. SENSOR

IGNITER R3LR3_ FLAME ROLLDUT
SWITCH

SID
PRIMARY
GAG _

F=_

LIMIT{NV_I _',

JI59
Pt59

HONEYWELL
_--..OAS VALVE

sE_ACKUPy(J_

B6 "_

CDMBG_TION AIR
INDUCER MOTOR

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YF..Lt.U*
YELLOW

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BLACK

$21
SECONDARY
GAS LIMIT
CBB 'ICIRCUIT
BREAKER
E_
/_

It'll

---- --

$21
SECONDARY

,_.¢iiJjI

BLOWER
BAG
INDOOR
LIMIT
MOTOR

UNITS

USE COPPER

$51
INTERLOCK

Ll_.e__O

....

LINE VOLTAGE FIELD INSTALLED
CLASS II VOLTAGE FIELD WIRING

DENOTES

OPTIONAL

T_I_'I

CONDUCTORS

_R_IN_"

ICAPACITOR
DOOR

TO ANY ORE CONNECTIDN
PARK TERMINALS ARE UNPO_ERED
TERMINALS,ALL
UNUSED MOTOR LEADS

/_X_H_

OUTDOOR
UNIT

JACKPLUG CHART
CONTROL
IJACKIPLUG-COMB.AIR
INDUCER
IJACK/PLUG-SECDNDARY
LIMIT
_ACK/PLUG-INDUCER/IGNITER
UACK/PLUG-IGNITION

IMPORTANTTO PREVENT MOTOR BURROUT,NEVER
CONNECT MORE THAN ONE MDTOR LEAD

-36C-OR0

SETTINGS

IF ANY WIRE IN THIS APPLIANCE IS REPLACED,IT
MUST BE REPLACED WITH WIRE OF LIKE SIZE,
RATING, INSULATION THICKNESS, AND TERMINATION.

PISS

(Et)

•

YELLOW

BROWN

WARNINGELECTRIC SHOCK HAZARD,CAN CAUSE INJURY
OR DEATH.UNIT MUST BE GROUNDED IN ACCORDANCE
WITH NATIONAL AND LOCAL CODES.

P5B

_B_JA_
IJ.PB4
IJ,PI35
_PIS_
,P159

TRAHSPORMER
....
BLOWER
IGNITION
CDNTROL
P156
(E4)_

H_U I
RED

CD_

JI55

III

BROWN
DROWN

THERMOSTAT HEAT ANTICIPATION

COMBUSTION AIR\/OJ
PRDVING SWITCH

AIR
SWITCH

SI
ROOM THERMOSTAT

_
<_

_r_

B#o'
INTERLOCK

YAH*

RED II RRn_
BROWN
IIYELLOW
YFI I _ II t_Fr)
RED
YELLLY#
BLOWER SPEED SELECTION

WHITEGVoDGERG
6AS VALVE

JB4

360-DgO
48C-ODD

pLROEWSgRS
E
SWITCH
(ALTERNATE1

=_AN

BRD_
R_

I
_
I I I Si_

[:_.,= H_A=

2AB'04_._._55 IYELLOW I RED I
365-0'$5
IYFII _ I RFn I

ONLY,
QUICK

FEMALE

_N_I

FIELD SUPPLIED

I
I I

ACC,WIRE,

S113 USED OH DSD, I I0
AND 155 UNITS ONLY.
St
ROOMTHERMOSTAT

II M

.....

),.,''•1

--_ "_-_

_COOL/_z'_

tt%

COMPONENTS

I,_OVA_
LIIz_oE
V XFMR

JSD_

)
PIS9jI
5g

J84

_
--

SEE BLUR
SPEED CHART

_z_
.Jw

_="
_.r_

YELLOW

R33

_,?
ADZF_'N

,o,

(_'EEDUIP.ENT
I I I L----..__

_o_ND I I'

"'I

__J

WHITE

FIGURE 57

Page 36

, .

P_s,F
v

_JSB

A92

s"s_-/%j__
_I($) Qv'

FORYOURSAFETYREADBEFOREOPERATING

BEFORE LIGHTING the unit, smell all around the furnace
area for gas, Be sure to smell next to the floor because
some gas is heavier than air and will settle on the floor.
The gas valve on the G51MP may be equipped with either a
gas control lever or gas control knob. Use only your hand to
push the lever or turn the gas control knob, Never use tools.
If the the lever will not move or the knob will not push in or
turn by hand, do not try to repair it. Call a qualified service
technician. Force or attempted repair may result in a fire or
explosion.

_WARNING

Placing the furnace into operation:
G51MP units are equipped with a SureLight ¢ ignition system, Do not attempt to manually light burners on this furnace. 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 SureLight ¢ ignition
system,

,WARNING

a,WARNING
,CAUTION
Gas Valve Operation (Figures 58 and 60)
1 - STOP! Read the safety information at the beginning of
this section.
Priming

Condensate

Trap

The condensate trap should be primed with water prior to
start-up to ensure proper condensate drainage. Either pour
10 fl, oz. (300 ml) of water into the trap, or follow these steps
to prime the trap:

Set the thermostat to the lowest setting,

3- Turn off all electrical power to the unit,

1 - Follow the lighting instructions to place the unit into operation,

4- This furnace is equipped with an ignition device which
automatically lights the burners. Do not try to light the
burners by hand,

2 - Set the thermostat to initiate a heating demand.

5 - Remove the upper access panel,

3 - Allow the burners to fire for approximately 3 minutes,

6 - White Rodgers 36G Gas Valve or HoneywellVR8205
Gas Valve with ON/OFF Lever - Switch gas valve lever
to OFF. See figure 58 for the White Rodgers 36G
valve. See figure 59 for the HoneywellVR8205 valve,
Honeywell VR8205 Gas Valve with Knob - Turn knob
on gas valve clockwise _
to OFF. Do not force. See
figure 60,

Adjust the thermostat
mand,

to deactivate the heating de-

5 - Wait for the combustion air inducer to stop, Set the
thermostat to initiate a heating demand and again allow the burners to fire for approximately 3 minutes.
6-

Adjust the thermostat to deactivate the heating demand and again wait for the combustion air inducer to
stop. At this point, the trap should be primed with sufficient water to ensure proper condensate drain operation,

Page 37

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.

Turning Off Gas to Unit

White Rodgers 36G Series Gas Valve

1 - Set the thermostat to the lowest setting,
ESSURE
POST

2 - Turn off all electrical power to the unit if service is to be
performed,
3 - Remove the upper access panel.

_:::__UTLET

INLETIPRESSURE
POST

IIIHr"_q

_'>.

III

_:_

t_v_/'--"_--_

4 - White Rodgers 36G Gas Valve or HoneywellVR8205
Gas Valve with ON/OFF Lever - Switch gas valve lever
to OFF,
Honeywell VR8205 Gas Valve with Knob - Turn knob
on gas valve clockwise _lb to OFF, Do not force,

MANIFOLD
PRESSURE
ADJUSTMENT
SCREW

GAS VALVE SHOWN IN OFF POSITION

FIGURE 58

5 - Replace the upper access panel,
Honeywell

VR8205

I_J_IIFOLD _
PRESSURE _,_
ADJUSTMENT_
SCREW
_
(under
_
barbed
,

Gas Valve

with

ON/OFF

Le-

Heating Sequence

1 - When thermostat calls for heat, combustion air inducer
starts.

MANIFOLD
PRESSURE
OUTLET

2 - Combustion air pressure switch proves blower operation, Switch is factory set and requires no adjustment,

INLET
fitting) /_==_ _
PRESSURE
PORT

3 - After a 15-second prepurge, the hot surface ignitor energizes,

._--

4- After a 20-second ignitor warm-up period, the gas
valve solenoid opens.

GAS VALVE SHOWN IN ON POSITION

FIGURE 59

5 - Gas is ignited, flame sensor proves the flame, and the
combustion process continues.

Honeywell VR8205 Gas Valve with Control Knob
MANIFOLD
PRESSURE
_
ADJ USTM ENT'_.),._
I ,,'_

""_

barbedI((o'_/ 1/"
fitting),_!'k_'(_i---,
INLET /
PRESSURE

PORT

I (,(_(._

6 - If flame is not detected after first ignition trial, the ignition control will repeat steps 3 and 4 four more times
before locking out the gas valve ("WATCHGUARD"
flame failure mode), The ignition control will then automatically repeat steps 1 through 6 after 60 minutes,

MANIFOLD
_,/
_ 4_

SCREW
(under

Of Operation

_
_

t
"

\
_

/ "

L?°N/'_
_

P (_I_F_UTRE

7 - To interrupt the 60-minute "WATCHGUARD" period,
move thermostat from "Heat" to "OFF" then back to
"Heat", Heating sequence then restarts at step 1,

oF j"/

GAS VALVE SHOWN IN OFF POSITION

FIGURE 60
8 - White Rodgers 36G Gas Valve or HoneyweflVR8205
Gas Valve with ON/OFF Lever - Switch gas valve lever
to ON. See figure 58 for the White Rodgers 36G valve.
See figure 59 for the HoneyweflVR8205 valve.
Honeywell VR8205 Gas Valve with Knob - Turn knob
on gas valve counterclockwise 41_ to ON, Do not
force. See figure 60,
9 - Replace the upper access panel,
10- Turn on all electrical power to to the unit,
11- Set the thermostat to desired setting,
NOTE - When unit is initially started, steps 1 through 11
may need to be repeated to purge air from gas line,
12- If the appliance will not operate, follow the instructions
"Turning Off Gas to Unit" and call your service technician or gas supplier.

Gas Flow (Approximate)
1 - Operate unit at least 15 minutes before checking gas
flow. Determine the time in seconds for one revolutions of gas through the meter, A portable LP gas meter (17Y44) is available for LP applications,
2 - Compare the number of seconds and the gas meter
size in table 10 to determine the gas flow rate. Multiply
the gas flow rate by the heating value to determine the
unit input rate, If manifold pressure is correct and the
unit input rate is incorrect, check gas orifices for proper
size and restriction,
3 - Remove temporary gas meter if installed,
NOTE - To obtain accurate reading, shut off all other gas
appliances connected to meter,

Page 38

TABLE 10

XI,IMPORTANT

Gas Flow Rate (Ft._/Hr.)
Gas Meter Size
Seconds for 1
Revolution
1/2 cu ft Dial
1 cu ft Dial
10
18O
36O
12
15O
3OO
14
129
257
16
113
225
18
100
2OO
2O
90
180
22
82
164
24
75
15O
26
69
138
28
64
129
3O
6O
120
32
56
113
34
1O6
53
36
5O
100
38
47
95
40
45
90
42
43
86
44
41
82
46
39
78
48
38
75
5O
36
72
52
69
35
54
33
67
56
32
64
58
31
62
6O
3O
6O

NOTE - In Canada, certification for installations at elevations over 4500 feet (1372 m) is the jurisdiction of local authorities.
The manifold pressure may require adjustment to ensure
proper operation at higher altitudes. Refer to table 11 for
proper manifold pressure settings at varying altitudes.
Table 12 lists required pressure switch changes and conversion kits at varying altitudes.
The combustion air pressure switches are factory-set and
require no adjustment.
TABLE 11
Manifold Pressure (Outlet) inches w.c.
Fue
I

Model
Input
Sizes

04500

Nat.
Gas

All
sizes

3.5

3.5*

L.P.
Gas

All
sizes

10.0"*

Gas Pressure
1 - Check the gas line pressure with the unit firing at maximum rate. A minimum of 4.5 in, w,c. for natural gas or
11,0 in, w,c, for LP/propane gas should be maintained,
2-

After the line pressure has been checked and adjusted, check the regulator pressure. A natural gas to
LP/propane gas changeover kit is required to convert

750110,000

*Conversion kit required for appfications at altitudes above 7501
ft. above sea level.
**Conversion kit required for appfications at aft altitudes.

the unit, Manifold pressures are given in table 11, See
figures 58, 59 and 60 for the location of the manifold
pressure adjustment screws,
Conversion

Altitude (feet)
4501 550165015500
6500
7500

NOTE

- A natural

to L.P. propane

necessary

to convert

installation

instruction

gas changeover

this unit. Refer to the changeover
for the conversion

procedure.

TABLE 12
Kit and Pressure Switch Requirements at Varying Altitudes
Altitude

Model
Input
Size

-O45
-070
-090
-110

-135

0 - 4500 ft.
Gas

4,501 -7500 ft.
(1373-2286
m)

(0 - 1372 m)
Required
Conversion
Kit

Pressure
Switch

7501-10,000 ft.
(2287-3048
m)

Required
Conversion
Kit

Pressure
Switch

Required
Conversion
Kit

Pressure
Switch

Nat,

N/A

No Change

N/A

No Change

59M16

95M22

LPG

83M74

No Change

83M74

83M75

95M22

Nat.

N/A

No Change

N/A

No Change
56M05

59M16

56M06

LPG

83M74

56M05

83M75

56M06

Nat.

N/A

75M20

59M16

56M07

LPG

83M74

No Change
No Change
No Change

83M74

75M20

83M75

56M07

Nat.

N/A

No Change

N/A

75M20

59M16

56M07

LPG

83M74

No Change

83M74

75M20

83M75

56M07

Nat.

N/A

No Change

N/A

56M04

59M16

60M35

LPG

83M74
56M04
83M75
60M35
83M74
No Change
Pressure switch is factory set, No adjustment necessary. All models use the factory installed pressure switch from 0-4500 feet (0-1370 m).

Page 39

kit is
kit

2 - Check for the correct voltage at the furnace (furnace
operating).
Primary and Secondary

3 - Check amp-draw on the blower motor.
Motor Nameplate
Actual
NOTE - Do not secure the electrical conduit directly to the
air ducts or structure,

Limits

The primary limit is located on the heating compartment
vestibule panel, The secondary limits are located in the
blower compartment, attached to the back side of the blower, These limits are factory set and require no adjustment,
Flame Rollout Switches

Blower Speeds
NOTE - CFM readings are taken external to unit with a dry
evaporator coil and without accessories,
1 - Turn off electrical power to furnace,
2 - Remove blower access panel,
3 - Disconnect existing speed tap at control board speed
terminal.

(Two)

These manually reset switches are located on the burner
box. If tripped, check for adequate combustion air before
resetting,
Pressure Switches (Two)
The pressure switches are located in the heating compartment on the combustion air inducer, These switches check

NO TE - Termination of any unused motor leads must be insulated.

for proper combustion air inducer operation before allowing ignition trial, The switches are factory-set and require
no adjustment.
Temperature

4 - Refer to blower speed selection chart on unit wiring
diagram for desired heating or cooling speed,
5- Connect selected speed tap at control board speed
terminal.

Rise

After the furnace has been started and supply and return
air temperatures have been allowed to stabilize, check the
temperature rise. If necessary, adjust the blower speed to
maintain the temperature rise within the range shown on
the unit nameplate, Increase the blower speed to decrease
the temperature. Decrease the blower speed to increase
the temperature rise. Failure to adjust the temperature rise
may cause erratic limit operation,
Fan Control
Heating Mode -- The fan on delay of 45 seconds is not adjustable. The fan off delay (amount of time that the blower
operates after the heat demand has been satisfied) may be
adjusted by setting $1 switches 1 and 2 located on the
SureLight e control. The unit is shipped with a factory fan off
setting of 90 seconds. The fan off delay affects comfort and
is adjustable to satisfy individual applications. Adjust the
fan off delay to achieve a supply air temperature between
90 ° and 110°F at the exact moment that the blower is deenergized. Longer off delay settings provide lower return
air temperatures; shorter settings provide higher return air
temperatures. See figure 56.
Cooling Mode -- The cooling mode fan off delay (amount
of time that the blower operates after the cooling demand
has been satisfied) may be adjusted by setting $1 switch 3
located on the SureLight @control. In the off position, the
cooling fan off delay is 2 seconds. In the on position, the
cooling fan off delay is 45 seconds. See figure 56,
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.
Electrical
1 - Check all wiring for loose connections,

6 - Resecure blower access panel.
7 - Turn on electrical power to furnace,
Electronic Ignition
The SureLight ® integrated control 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. This type of lockout is usually due to low
gas line pressure, 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,
Exhaust and Air Intake Pipe
1 - Check exhaust and air intake connections for tightness
and to make sure there is no blockage,
2- Are pressure switches closed? Obstructed exhaust
pipe will cause unit to shut off at pressure switches,
Check termination for blockages,
3- Reset manual flame rollout switches on burner box
cover.
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?
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,

Page 40

If cleaning the heat exchanger becomes necessary, follow
the below procedures and refer to figure 1 when disassembling unit. Use papers or protective covering in front of furnace while removing heat exchanger assembly.

,&WARNING

1 - Turn off electrical and gas supplies to the furnace.
2 - Remove the upper and lower furnace access panels,
3 - Mark all gas valve wires and disconnect them from
valve.
4 - Remove gas supply line connected to gas valve, Remove gas valve/manifold assembly.
5 - Remove sensor wire from sensor, Disconnect 2-pin or
3-pin plug from the ignitor.
6 - Disconnect wires from flame roll-out switches.

At the beginning of each heating season, system should be
checked as follows by a qualified service technician:
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,

AWARNING

Filters
All G51MP filters are installed external to the unit. Filters
should be inspected monthly. Clean or replace the filters
when necessary to ensure proper furnace operation. Table
3 lists recommended filter sizes,
Exhaust and air intake pipes
Check the exhaust and air intake pipes and all connections
for tightness and to make sure there is no blockage,
Electrical
1 - Check all wiring for loose connections.
2 - Check for the correct voltage at the furnace (furnace
operating),

8 - Loosen three clamps and remove flexible exhaust tee,
9 - Remove 3/8 inch rubber cap from condensate drain
plug and drain, Replace cap after draining.
10 - Disconnect condensate drain line from the condensate trap, Remove condensate trap (it may be necessary to cut drain pipe), Remove screws that secure
condensate collars to either side of the furnace and remove collars. Remove drain tubes from cold end
header collector box,
11 - Disconnect condensate drain tubing from flue collar,
Remove screws that secure both flue collars into
place. Remove flue collars, It may be necessary to cut
the exiting exhaust pipe for removal of the fittings,
12 - Disconnect the 2-pin plug from the combustion air inducer, Disconnect the two wires to the secondary limit,
if applicable. Remove four screws which secure combustion air inducer to collector box Remove combustion air inducer assembly, Remove ground wire from
vest panel,
13 - Mark and disconnect all combustion air pressure tubing from cold end header collector box.
14 - Mark and remove wires from pressure switches. Remove pressure switches, Keep tubing attached to
pressure switches.
15 - Remove electrical junction box from the side of the furnace,

3 - Check amp-draw on the blower motor.
Motor Nameplate
Actual
Winterizing and Condensate Trap Care
1 - Turn off power to the unit,
2 - Have a shallow pan ready to empty condensate water.
3 - Remove the drain plug from the condensate trap and
empty water, Inspect the trap then reinstall the drain
plug,
Cleaning

7 - Remove burner box cover and remove four burner box
screws at the vestibule panel and remove burner box,
Set burner box assembly aside.
NOTE - If necessary, clean burners at this time, Follow
procedures outlined in Burner Cleaning section.

Heat Exchanger

Page 41

16 - Mark and disconnect any remaining wiring to heating
compartment components. Disengage strain relief
bushing and pull wiring and bushing through the hole
in the blower deck.
17 - Remove the primary limit from the vestibule panel,
18 - Remove two screws from the front cabinet flange at
the blower deck. Spread cabinet sides slightly to allow
clearance for removal of heat exchanger,

19- Removescrewsalongvestibulesidesand bottom
whichsecurevestibulepanelandheatexchanger
assemblyto cabinet.Removetwoscrewsfromblower
railwhichsecurebottomheatexchanger
flange,Removeheatexchanger
fromfurnacecabinet,
20- Backwashheatexchanger
withsoapywatersolution
or steam,If steamis usedit mustbe below275°F
(135°C).

38 - Secure burner box assembly to vestibule panel using
four existing screws. Make sure burners line up in
center of burner ports.
39- Reinstall gas valve manifold assembly,
gas supply line to gas valve,
40 - Reinstall burner box cover,
41 - Reconnect wires to gas valve,
42 - Replace the blower compartment

21 - Thoroughly rinse and drain the heat exchanger. Soap
solutions can be corrosive, Take care to rinse entire
assembly.

Reconnect

access panel.

43 - Refer to instruction on verifying gas and electrical connections when re-establishing supplies.

22 - Reinstall heat exchanger into cabinet making sure that
the clamshells of the heat exchanger assembly are
resting on the support located at the rear of the cabinet. Remove the indoor blower to view this area
through the blower opening,
23 - Re-secure the supporting screws along the vestibule
sides and bottom to the cabinet,

44 - Follow lighting instructions to light and operate furnace for 5 minutes to ensure that heat exchanger is
clean and dry and that furnace is operating properly,
45 - Replace heating compartment access panel,
Cleaning the Burner Assembly
1 - Turn off electrical and gas power supplies to furnace.
Remove upper and lower furnace access panels,

24- Reinstall cabinet screws on front flange at blower
deck.

2 - Mark all gas valve wires and disconnect them from the
valve.

25 - Reinstall the primary limit on the vestibule panel.

3 - Disconnect the gas supply line from the gas valve, Remove gas valve/manifold assembly.
4 - Mark and disconnect sensor wire from the sensor. Disconnect 2-pin plug from the ignitor at the burner box.
5 - Remove burner box cover and remove four screws
which secure burner box assembly to vest panel, Remove burner box from the unit,

26 - Route heating component wiring through hole in blower deck and reinsert strain relief bushing.
27 - Reinstall pressure switches and reconnect pressure
switch wiring.
28 - Carefully connect combustion air pressure switch hosing from pressure switches to proper stubs on cold end
header collector box,
29 - Reinstall condensate collars on each side of the furnace. Reconnect drain tubing to collector box,
30 - Reinstall condensate trap on same side as exhaust
pipe. Reconnect condensate drain line to the condensate trap.

7 - Reconnect the sensor wire and reconnect the 2-pin
plug to the ignitor wiring harness.

31 - Reinstall electrical junction box.
32 - Reinstall the combustion air inducer. Reconnect the
2-pin or 3-pin plug to the wire harness, Reconnect the
two wires to the secondary limit, if applicable,
33 - Use securing screws to reinstall flue collars to either
side of the furnace. Reconnect exhaust piping and exhaust drain tubing,

6 - Use the soft brush attachment on a vacuum cleaner to
gently clean the face of the burners, Visually inspect
the inside of the burners and crossovers for any blockage caused by foreign matter, Remove any blockage,

8 - Reinstall the burner box assembly using the existing
four screws. Make sure that the burners line up in the
center of the burner ports.
9 - Reinstall the gas valve manifold assembly, Reconnect
the gas supply line to the gas valve, Reinstall the burner box cover,
10 - Reconnect the gas valve wires to the gas valve.

34 - Replace flexible exhaust tee on combustion air inducer and flue collars, Secure using three existing hose
clamps,

11 - Replace the blower compartment access panel,

35 - Reinstall burner box assembly in vestibule area,
36 - Reconnect flame roll-out switch wires,

13- Follow lighting instructions to light and operate furnace for 5 minutes to ensure that heat exchanger is
clean and dry and that furnace is operating properly,

37 - Reconnect sensor wire and reconnect 2-pin plug from
ignitor,

12 - Refer to instruction on verifying gas and electrical connections when re-establishing supplies.

14 - Replace heating compartment access panel,

Page 42

ThefollowingrepairpartsareavailablethroughLennoxdealers.Whenorderingparts,includethecomplete
furnacemodel
numberlistedontheCSAnameplate
-- Example:
G51MP-24B-045-1.
CabinetParts
Heating Parts
Upperaccesspanel
Flame Sensor
Bloweraccesspanel
Heat exchanger assembly
Gas manifold
Topcap
ControlPanelParts
Combustion air inducer
Gas valve
Transformer
Main burner cluster
SureLight
_ integrated
controlboard
Main burner orifices
Doorinterlockswitch
Pressure switches
Circuitbreaker
Ignitor
Primary limit control
Secondary limit control
Flame rollout switches
Combustion air inducer auxiliary limit

Blower Parts
Blower wheel
Motor
Motor mounting frame
Motor capacitor
Blower housing cutoff plate

DIAGNOSTIC

CODES

Make sure to Identify LED'S Correctly.
Refer to Installation

DS1
(Red or Green)

Instructions

for control board layout.

DS2
(Green)

SIMULTANEOUS
SLOWFLASH

SIMULTANEOUS

FAST FLASH

SLOW FLASH

DESCRIPTION
Power on -- Normal operation.
Also signaled during cooling and continuous fan.
Normal operation

-- Signaled

when

heating

demand initiated at thermostat.

Primary or secondary limit switch open. Limit must close within 3 minutes or unit
goes into 1-hour Watchguard.
Pressure switch open;

OFF

ALTERNATING
SLOWFLASH

SLOW FLASH

OR: Blocked inlet/exhaust vent;
OR: Condensate line blocked;
OR: Pressure switch closed prior to activation of combustion air inducer.

ALTERNATING
SLOWFLASH

Watchguard

SLOW FLASH

OFF

SLOW FLASH

-- Burners failed to ignite, limit open
sense lost 5 times in one heating cycle.

longer

than 3

minutes,

flame

Flame sensed without gas valve energized.
Rollout switch open.

OFF

FAST FLASH

SLOW FLASH

Main power polarity reversed. Switch line and neutral. Improper main ground.

SLOW FLASH

FAST FLASH

Low flame signal. Check flame sensor.

ALTERNATING
FASTFLASH

The following conditions are sensed during the ignitor warm-up period only:
1) Improper main ground;
2) Broken ignitor; OR: Open ignitor circuit;
3) Line voltage below 75 volts.

Circuit board failure or control wired incorrectly. Check 24-volt and 115-volt
connections to board.

NOTE - Slow flash rate equals 1 Hz (one flash per second). Fast flash rate equals 3 Hz (three flashes per second).
Drop out flame sense current = O.15 - 0.24 microAmps.

Page 43

SURELIGHTCONTROL
HEATING SEQUENCE OF OPERATION

NORMAL HEATING MODE

CONTROL SELF'-CHECK
I
,IF
v

aYES _

IS POLARITY

DLSIEA##ADS2 FAST I
FLASH. SIGNAL
I NO
HOLDS UNTIL UNIT ISI_
PROPERLY
--

I
I,-,_
J NO |
|

ABNORMAL

POWER

OKAY'_
"

-I

GROUND.J'--_I PROPERGROUND?
ROLLOUT SWITCHES

Y SI

"i
I

IS VOLTAGE

CLOSED?

BURNER

.q
I

OFF'_

I Ni

I_1-

I SEQUENCE

DS1 -- SLOW FLASH
NORMAL
OPERATION:
DS2 -- SLOW
FLASH

I
_1

THERMOSTAT CALLS FOR HEAT:
DS1 -- FAST FLASH
DS2 -- FAST FLASH

HOLDS UNT L ROLLOUT SW TCH CLOSES

INDOOR BLOWER ON HEATING SPEED.
DSl -- SLOW FLASH
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
DS2 -- OFF

ARE COMBUSTION
PRESSURE SWITCHES

AIR

OPEN?

IS COMBUSTION
ENERGIZED?
(HUM
TERMINALS AIR
AREINDUCER
ENERGIZED
WITH CAI)

GAS VALVE OFF.
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF WITH DELAY.
DSl OFF
DS2 SLOW FLASH
(Sequence holds until pressure switch
closes or thermostat resets control.)

YES _

RISES ABOVE 75 VOLTS.

YES

GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF WITH DELAY.
DSI --ON. DS2-- SLOW FLASH.

YES

DS1 AND DS2 ALTERNATING FAST
FLASH. SIGNAL HOLDS UNTIL VOLTAGE

I_
_1
FLAME CHECK)

POLARITY REVERSED.
DSI - FAST FLASH
DS2 --SLOW FLASH

(CONTINUOUS

OSlo%"

ABOVE 75 VOLTS?
YES_I

ON.

GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER DELAY OFF.

AIR INDUCER

INDOOR BLOWER ON.
DS1 ALTERNATING FAST FLASH
DS2 ALTERNATING FAST FLASH
CHECK FOR BROKEN
IGNITOR OR

I'
,
_

HEATING MODE

OFF. COMBUSTION

I -II

REVERSED?

.[
•
ISTHERE

GAS VALVE

I PRESSURE

IN WATCHGUARD

MODE.

I I

NI___I GASVALVEOFF.COMBUSTION
AIRINDUCER
OFF.

HAVE COMBUSTION AIR PRESSURE
SWITCHES CLOSED IN 2.5 MINUTES?

YES _
15-SECOND COMBUSTION AIR INDUCER PREPURGE
N T ATED BY CLOSED PRESSURE SW TCH.

I
I
I

YES
CONTINUED

SWITCHES

Page 44

INDOOR BLOWER OFF WITH DELAY.
DSl -- OFF. DS2 -- SLOW FLASH,
S 5-M NUTE RESET PER OD COMPLETE?

NORMAL HEATING MODE

ABNORMALHEATING

5-SECOND
COMBUSTION
INDUCERSWITCH.
PREPURGE
INITIATED
BY CLOSED AIR
PRESSURE
YES
i

4-SECOND TRIAL FOR IGNITION.
GAS VALVE OPENS. IGNITOR ENERGIZED
UP TO 4 SECONDS.

4 SECONDS

,,-

YES

s, .AL

I
DS1 & DS2
I ALTERNATING
NOI FAST FLASH.

CONNECTED?_'[ ___

FOR

FLAME STABILIZATION

YES

IS IGNITOR INTACT AND

I
YES

9 '
IS VOLTAGE ABOVE 75 VOLTS.

NO
•
| YES

IGNITOR WARM-UP -- 20 SECONDS.
YES

,
&'_P1

MODE

PERIOD.

FLAME RECTIFICATION CURRENT
CHECK, CAN FLAME BE PROVEN WITHIN
4 SECONDS AFTER GAS VALVE OPENS?
( > 0.24 microamps)

GAS VALVE OFF. COMBUSTION AIR INDUCER
INDOORBLOWEROFF.

_,]

ON.

INo,HAS
CONTROL
FA
LED
TO
SENSE
FLAME
FOR
I

'1 FIVE CONSECUTIVE

' I
/

TRIES DURING A SINGLE

HEATDEMAND?
t

i i I ,GN,T,ON
WATCHGUARD
MODE
GAS
VALVE
OFF
i
t_

COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF WITH DELAY
DSl ALT. SLOW FLASH DS2 ALT. SLOW FLASH
IS 60-MINUTE RESET PERIOD COMPLETE?

YES

/
I

YES _.

YES
HAS CONTROL

FLAME PRESENT?

RESET IGNITION

I
I

_l_'

SEQUENCEFOURTIMES?

YES

FLAME SIGNAL ABOVE 0.34 MICROAMPS?
YES

INDOOR BLOWER ON DELAY BEGINS
(45 seconds.)
YES

NO
ROLLOUT SWITCHES

YES l
LIMIT SWITCH WATCHGUARD MODE. GAS
VALVE OFF. COMB. AIR
INDUCER OFF. INDOOR
BLOWER OFF WITH
DELAY. DSl - SLOW
FLASH DS2 - ON. IS
60MINUTE RESET
PERIOD COMPLETE?

YES _
HAVE PRI MARY/S ECO N DARY/CAI
AUX. LIMITS RESET (CLOSED)
WITHIN 3 MINUTES?

YES

GAS VALVE DE-ENERGIZED.
COMBUSTION AIR INDUCER
DE-ENERGIZED.INDOOR
BLOWER
ON UNTIL SWITCHES CLOSE. DS1
-- SLOW FLASH. DS2 -- ON.
IS LIMIT SWITCH CLOSED?

PRIMARY AND SECONDARY LIMIT
SWITCHES CLOSED?
COMBUSTION AIR INDUCER
AUXILIARY LIMIT SWITCH CLOSED?

LOW FLAME SIGNAL
(Does not affect operation of
control)
DSl -- SLOW FLASH
DS2 -- }-ASI FLASH

CLOSED?

NO _f
YES

GAS VALVE POWER OFF.
COMBUSTION AIR INDUCER POWER OFF.
INDOOR BLOWER OFF WITH DELAY
DSl -- ON. DS2 -- SLOW FLASH.
SEQUENCE HOLDS UNTIL ROLLOUT SWITCH IS RESET.

COMBUSTION AIR PRESSURE
SWITCH CLOSED?
I_-_
YES

THERMOSTAT

COMBUST

DEMAND SATISFIED.

YES _

DS1 & DS2 SIMULTANEOUS
YES

GAS VALVE DE-ENERGIZED.

SLOW FLASHES.

ON A R NDUCER ON

INDOOR BLOWER OFF WITH DELAY
DS1 -- OFF. DS2 -- SLOW FLASH.
HAS CAB SW TCH CLOSED

N 2.5 M NUTES?

NO_

COMB. AIR INDUCER CONTINUES 5-SECOND
POST PURGE AFTER T'STAT DEMAND IS SATISFIED,
INDOOR AIR BLOWER COMPLETES SELECTED "OFF"
DELAY BEFORE SHUTT NG OFF.

WATCHGUARD

Page 45

MODE.

YES

I
I

YES

Iii

SURELIGHT CONTROL
COOLING SEQUENCE OF OPERATION
NORMAL COOLING MODE
POWER ON.

iGNITION CONTROL

ABNORMAL

COOLING MODE

MAIN POWER ON.

GAS VALVE OFF. COMBUSTION AIR INDUCER
OFF.
INDOOR BLOWER OFF WITH NORMAL DELAY.
SIGNAL CIRCUIT BOARD FAILURE AT DSl & DS2.

CONTROL
DIAGNOSTIC
CHECK.
IS
CONTROLSELF
OPERATING
NORMALLY?

.......................................
I1"_

DS1 AND DS2
ALTERNATING

FAST

I NO ,

FLASH. SIGNAL
_
I HOLDS UNTIL UNIT IS I_1

POLARITY

REVERSED?

NO 1
•

IS THERE
PROPER GROUND?

DSl

_
I_IABOVE

ERRUr

FAST

IVl_ll_

FLASH

rUVVER

DS2

SLOW

I U

REOE

FLASH.

bUl'_

DS1 AND DS2 ALTERNATING
IS VOLTAGE
75 VOLTS?

I RUL,

FAST

FLASH. SIGNAL HOLDS UNTIL VOLTAGE
RISES ABOVE 75 VOLTS,

LPROPERLY
GROUND.
j
NO

RO LLO UATR_V_
TC LHESTMyESO_'TOHREsD
CL_)NTEI
N UO U_ LY '1--_

CHECK ISFOR
MAINMAIN
BURNER
BURNER
FLAME
FLAME
OFF?SENSE.

GAS VALVE OFF

THROUGHOUT

COOLING CYCLE.

THERMOSTAT
CALLS
FOR
COOLING.
1
COMPRESSOR
CONTACTOR AND SYSTEM FAN
ENERGIZED WITH 2-SECOND
DELAY. COOL
SPEED TERMINAL IS ENERGIZED. EAC
TERMINAL IS ENERGIZED,

THERMOSTAT

COMPRESSOR

OPENS.

OFF.

SYSTEM FAN AND EAC TERM. OFF
WITH2-OR45-SECOND
DELAY,

Page 46

AIR INDUCER OFF

S ES I_ECR_R_LL_DW EuBROi,
iFRV_o
IAiHu:RO_MwTA_:&:AY_ _ S.
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF WITH NORMAL DELAY,
SIGNAL CIRCUIT BOARD FAILURE AT DSl & DS2.
SEQUENCE HOLDS UNTIL FLAME IS NOT SENSED,

I OSl OS :S OW1AS AT
UNCHANGED

COMBUSTION

A,.S

SURELIGHT CONTROL
CONTINUOUS FAN SEQUENCE OF OPERATION

DS1 & DS2: SLOW FLASH RATE REMAINS
UNCHANGED THROUGHOUT SEQUENCE.

MANUAL FAN SELECTION MADE AT THERMOSTAT.
CONTROL (G) ENERGIZES INDOOR BLOWER AT
FAN SPEED. EAC TERM. IS ENERGIZED.

THERMOSTAT

CALLS FOR HEAT (W).

NO
THERMOSTAT

INDOOR BLOWER SWITCHES

TO COOL SPEED.

HUM (120 MAC & 24MAC)
TERMINALS ENERGIZED
WITH COMB.
+ AIR INDUCER.

INDOOR BLOWER SWITCHES TO HEAT SPEED
AFTER NORMAL DELAY.

+
I

THERMOSTAT

-4

YES

CALLS FOR COOLING.
YES

AND HUM TERMINALS ARE DE-ENERGIZED
THERMOSTAT
OPENS.
COMBUSTION
AIR INDUCER
FOLLOWING
5-SECOND
POST-PURGE.

OPENS.
m

INDOOR BLOWER SELECTED

TIME OFF DELAY BEGINS. I
m

AFTER DELAY, HEAT SPEED DE-ENERGIZED.
(Bower rema ns energ zed dur ng cont nuous fan mode).

INDOOR BLOWER SWITCHES TO FAN
SPEED. EAC TERM. REMAINS ENERGIZED.

Page 47

Step 1

Proposed

vent pipe size :

Equivalent

Step 2

Termination
kit catalog number :
Vent pipe equivalency
value from table 5 :

Step 3

Total number of 90 ° elbows required (indoors
X 5 =
equivalent feet of pipe

and outdoors)

Step 4

Total number of 45 ° elbows required (indoors
X 2.5 =
equivalent feet of pipe

and outdoors)

Step 5

Linear feet of straight

Step 6

Add equivalent feet of vent pipe listed in
steps 2 through 5.

pipe required

Feet

:
TOTAL

If the total is equal to, or less than, the allowable
maximum given in table 7, the proposed
pipe size is acceptable.
If the
total exceeds the maximum
allowed vent pipe length, repeat the process above using the next larger diameter pipe until
an acceptable
total is achieved.
NOTE - In Direct Vent systems, total the equivalent length of either the exhaust OR intake piping run, depending upon which
will be LONGER.
Intake and exhaust pipe diameter must be the same size and must be terminated
in the same pressure
zone. Intake and exhaust pipe should be roughly the same length.

Job Name

Job No,

Job Location

City

State

Installer
Unit Model No,
Serial No,

City
Technician

State

Heating

Date

Section

[]

Electrical Connections Tight?
Supply Voltage
Blower Motor Amps

Blower Motor H.P.

Gas Piping Connections
Tight & Leak-Tested?

[]

Fuel Type: Natural Gas?

[]

LP/Propane Gas?

[]

Furnace Btu Input
Line Pressure
Regulator Pressure
__
w,c, - Nat,:
Flue Connections Tight?
[]
Condensate Connections Tight? []
Combustion Gas Tested?
Fan Control Setting
(45 Seconds Fixed On)
Fan Control Off Setting
Filter Clean & Secure?

[]

CO2

w,c, - LP/Propane
Proper Draft?
[]

[]

Temperature
Vent Clear?

[]

Rise
[]

Thermostat
Calibrated?

[]

Heat Anticipator Properly Set?

[]

Page 48

Level?

[]

Source Exif Data:

File Type                       : PDF
File Type Extension             : pdf
MIME Type                       : application/pdf
PDF Version                     : 1.2
Linearized                      : No
Page Count                      : 48
Page Layout                     : SinglePage
Page Mode                       : UseNone
Producer                        : Goby Monitor Application version 4, 0, 0, 13
Create Date                     : Mon Jun 30 04:40:21 2008
Author                          : 
Title                           : 
Subject                         :

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LENNOX Furnace/Heater, Gas Manual L0806183

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