Comfortaire GUH97M User manual

507028-03 Page 1 of 66 Issue 1809
This is a safety alert symbol and should never be ignored. When you see this symbol on labels or in
manuals, be alert to the potential for personal injury or death.
This manual must be left with the homeowner for future reference.
INSTALLATION INSTRUCTIONS
GUH97M
Warm Air Gas Furnace
Upow/Horizontal Left and
Right Air Discharge
(P) 507028-03
*P507028-03*
Table of Contents
Unit Dimensions ..........................................................2
Parts Arrangement.......................................................3
A97USMV Gas Furnace..............................................4
Shipping and Packing List ...........................................4
Safety Information .......................................................4
General........................................................................6
Installation – Setting Equipment..................................6
Filters.........................................................................10
Duct System ..............................................................11
Venting Practices.......................................................13
Gas Piping.................................................................27
Electrical....................................................................30
Blower Performance..................................................44
Unit Start-Up..............................................................52
High Altitude Information ...........................................54
Other Unit Adjustments..............................................55
Heating Sequence of Operation ................................55
Service.......................................................................57
Integrated Control Diagnostic Codes.........................59
Repair Parts List........................................................61
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, personal
injury or loss of life. Installation and service must be
performed by a licensed professional installer (or
equivalent), service agency or the gas supplier.
WARNING
As with any mechanical equipment, personal injury can
result from contact with sharp sheet metal edges. Be
careful when you handle this equipment.
CAUTION
In non-communicating applications, a traditional
non-communication thermostat may be used.
In all cases, setup is critical to ensure proper system
operation.
Field wiring for non-communicating applications
is illustrated in these instructions.
NOTICE
A thermostat is not included.
Manufactured By
Comfort-Aire / Century
1900 Wellworth Ave.
Jackson, MI 49203

507028-03
Page 2 of 66Issue 1809
* NOTE - C/D20 size units that require second stage air
volumes over 1800 cfm (850 L/S) must have one of the
following:
•Single side return air with transition, to accommodate 20
x 25 x 1 in. (508 x 635 x 25 mm) air lter.
•Single side return air with optional RAB Return Air Base
• Bottom return air.
• Return air from both sides.
• Bottom and one side return air.
See Blower Performance Tables for additional information.
* Optional External Side Return Air Filter Kit is not for use
with the optional RAB Return Air Base.
Unit Dimensions
Model A B C D
in. mm in. mm in. mm in. mm
GUH97M070B3M 17-1/2 446 16-3/8 416 16 406 7-5/8 194
GUH97M090C3M
21 533 19-7/8 505 19-1/2 495 9-3/8 238
GUH97M090C4M
GUH97M090C5M
GUH97M110C5M
GUH97M135D5M 24-1/2 622 23-3/8 594 23 584 11-1/8 283

507028-03 Page 3 of 66 Issue 1809
Figure 1.
Parts Arrangement

507028-03
Page 4 of 66Issue 1809
GUH97M Gas Furnace
The GUH97M Category IV gas furnace is equipped with a
variable capacity, variable speed integrated control. Each
GUH97M is shipped ready for installation in the upflow,
horizontal left air discharge or horizontal right air
discharge position.
The furnace is equipped for installation in natural
gas applications only. A change over kit must be
ordered for LP/propane applications.
The GUH97M must be installed only as a Direct Vent
gas central furnace
NOTE: In Direct Vent installations, combustion air is
taken from outdoors and flue gases are discharged
outdoors. See Figure 2 for applications including roof
termination.
Figure 2.
Shipping and Packing List
1 - Assembled GUH97M unit.
1 - Bag assembly containing the following:
1 - Snap bushing
1 - Snap Plug
1 - Wire tie
1 - Condensate trap
1 - Condensate trap cap
1 - Condensate trap cap clamp
1 - 3/4” Threaded PVC street elbow
Check equipment for shipping damage. If you nd any
damage, immediately contact the last carrier.
Please refer to specication sheets for available
accessories.
Safety Information
DANGER OF EXPLOSION!
There are circumstances in which odorant used with
LP/Propane gas can lose its scent. In case of a leak,
LP/Propane gas will settle close to the oor and may be
difcult to smell. An LP/Propane leak detector should be
installed in all LP applications.
DANGER
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, personal
injury or loss of life. Installation and service must be
performed by a licensed professional installer (or
equivalent), service agency or the gas supplier.
WARNING
As with any mechanical equipment, personal injury can
result from contact with sharp sheet metal edges. Be
careful when you handle this equipment.
CAUTION
Use only the type of gas approved for use with this furnace.
Refer to unit nameplate.
Building Codes
In the USA, installation of gas furnaces must conform with
local building codes. In the absence of local codes, units
must be installed according to the current National Fuel
Gas Code (ANSI Z223.1/NFPA 54). The National Fuel Gas
Code is available from the American National Standards
Institute, Inc., 11 West 42nd Street, New York, NY 10036.
Installed Locations
In Canada, installation must conform with current National
Standard of Canada CSA-B149 Natural Gas and Propane
Installation Codes, local plumbing or waste water codes
and other applicable local codes.
The furnace is designed for installation clearances to
combustible material as listed on the unit nameplate and
in the tables in Figure 10 and Figure 11. Accessibility
and service clearances must take precedence over re
protection clearances.
NOTE: For installation on combustible oors, the furnace
shall not be installed directly on carpeting, tile, or other
combustible material other than wood ooring.

507028-03 Page 5 of 66 Issue 1809
For installation in a residential garage, the furnace must be
installed so that the burner(s) and the ignition source are
located no less than 18 inches (457 mm) above the oor.
The furnace must be located or protected to avoid physical
damage by vehicles. When a furnace is installed in a public
garage, hangar, or other building that has a hazardous
atmosphere, the furnace must be installed according to
recommended good practice requirements and current
National Fuel Gas Code or CSA B149 standards.
NOTE: Furnace must be adjusted to obtain a temperature
rise (100% percent capacity) within the range(s) specied
on the unit nameplate. Failure to do so may cause erratic
limit operation and may also result in premature heat
exchanger failure.
This furnace must be installed so that its electrical
components are protected from water.
Installed in Combination with a Cooling Coil
When this furnace is used with cooling units, it shall be
installed in parallel with, or on the upstream side of, cooling
units to avoid condensation in the heating compartment.
With a parallel ow arrangement, a damper (or other means
to control the ow of air) must adequately prevent chilled
air from entering the furnace. If the damper is manually
operated, it must be equipped to prevent operation of
either the heating or the cooling unit, unless it is in the full
HEAT or COOL setting. See Figure 3.
Figure 3.
Heating Unit Installed Parallel to Air Handler Unit
Heating Unit Installed Upstream of Cooling Unit
When installed, this furnace must be electrically grounded
according to local codes. In addition, in the United States,
installation must conform with the current National
Electric Code, ANSI/NFPA No. 70. The National Electric
Code (ANSI/NFPA No. 70) is available from the following
address:
National Fire Protection Association
1 Battery March Park
Quincy, MA 02269
NOTE: This furnace is designed for a minimum continuous
return air temperature of 60°F (16°C) or an intermittent
operation down to 55°F (13°C) dry bulb for cases where a
night setback thermostat is used. Return air temperature
must not exceed 85°F (29°C) dry bulb.
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.
Do Not set thermostat below 60° F (16° C) in heating
mode. Setting thermostat below 60° F (16° C) reduces
the number of heating cycles. Damage to the unit may
occur that is not covered by the warranty.
CAUTION
The GUH97M furnace may be installed in alcoves,
closets, attics, basements, garages, crawl spaces and
utility rooms.
This furnace design has not been CSA Certied for
installation in mobile homes, recreational vehicles, or
outdoors.
Use of Furnace as a Construction Heater
Gas furnaces manufactured on or after May 1, 2017,
are not permitted to be used in Canada for heating of
buildings or structures under construction.
WARNING
The following statement only applies to the US.
Comfort-Aire/Century does not recommend the use of
these units as a construction heater during any phase
of construction. Very low return air temperatures, harmful
vapors, construction dust and operation of the unit with
clogged or misplaced filters may damage the unit.
However, these units may be used for heating of buildings
or structures under construction in the US if the following
conditions are met to ensure proper operation:
•The vent system must be permanently installed per
these installation instructions.

507028-03
Page 6 of 66Issue 1809
•A room thermostat must control the furnace. The use
of xed 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 lters must be installed in the system and must be
maintained during construction.
•Air lters must be replaced upon construction
completion.
•The input rate and temperature rise must be set per
the furnace rating plate.
•One hundred percent (100%) outdoor air must be
provided for combustion air requirements during
construction.
•The furnace heat exchanger, components, duct system,
air lters and evaporator coils must be thoroughly
cleaned following nal construction cleanup.
•All furnace operating conditions (including ignition,
input rate, temperature rise and venting) must be
veried according to these installation instructions.
General
These units should not be installed in areas normally
subject to freezing temperatures.
CAUTION
These instructions are intended as a general guide and do
not supersede local codes in any way. Consult authorities
having jurisdiction before installation.
In addition to the requirements outlined previously, the
following general recommendations should be considered
when installing one of these furnaces:
•Place the furnace as close to the center of the air
distribution system as possible. The furnace should
also be located close to the vent termination point.
•When the furnace is installed in an attic or other
insulated space, keep insulation away from the
furnace.
•When the furnace is installed in an unconditioned
space, consider provisions required to prevent freezing
of condensate drain system.
Installation – Setting Equipment
Do not install the furnace on its front or its back. See
Figure 4.
WARNING
Do not connect the return air ducts to the back of the
furnace. Doing so will adversely affect the operation of
the safety control devices, which could result in personal
injury or death.
WARNING
Upow Applications
This gas furnace can be installed as shipped in the upow
position. Refer to Figure 10 for clearances.
Select a location that allows for the required clearances
that are listed on the unit nameplate. Also consider gas
supply connections, electrical supply, vent connection,
condensate trap and drain connections, and installation
and service clearances (24 inches [610 mm] at unit
front). The unit must be level from side to side, for proper
operation. It is recommended to tilt the unit slightly toward
the drain to insure proper drainage. See Figure 5.
Figure 4.
GUH97M applications which include side return air and a
condensate trap installed on the same side of the cabinet
(trap can be installed remotely within 5 feet) require either a
return air base or eld fabricated transition to accommodate
an optional IAQ accessory taller than 14.5”. See Figure 6.

507028-03 Page 7 of 66 Issue 1809
Figure 5.
UNIT MUST BE LEVEL SIDE TO SIDE IN ALL APPLICATIONS FOR PROPER OPERATION.
A SLIGHT TILT TOWARD THE DRAIN IS RECOMMENDED FOR PROPER DRAINAGE.
TILT THE UNIT SLIGHTLY (MAX. 1/2”) FROM BACK TO FRONT TO AID IN THE DRAINING OF THE HEAT
EXCHANGER.
Figure 6. Side Return Air
(with transition and lter) Figure 7. Removing the Bottom Panel
1/2" Max
1/2" Max

507028-03
Page 8 of 66Issue 1809
Figure 8. Optional Return Air Base
(Upow Applications Only)
FRONT VIEW
1Unit side return air
Opening
SIDE VIEW
3−1/4
(83)
1
23 (584)
Overall
(Maximum)
(584)
23
3/4
(19)
122−7/16
(570)
Overall
(Maximum)
SIDE RETURN
AIR OPENINGS
(Either Side)
5−5/8
(143)
1Minimum
11 (279)
2Maximum
14 (356)
(683)
26−7/8
7−1/4
(184)
FURNACE
FRONT
AIR FLOW
IF BASE
IS USED
WITHOUT
IAQ CABINET,
A SINGLE
RETURN AIR
PLENUM
MUST
COVER BOTH
UNIT AND
RETURN
AIR BASE
OPENINGS
INDOOR AIR
QUALITY
CABINET
AIR BASE
OPTIONAL
RETURN
CONDENSATE
TRAP
17−1/2 (446) B Width (50W98)
21 (533) C Width (50W99)
24−1/2 (622) D Width (51W00)
NOTE: Optional side return air lter kits are not for use with return air base.
1Both 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 eld. 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.
Removing the Bottom Panel
Remove the two screws that secure the bottom cap to the
furnace. Pivot the bottom cap down to release the bottom
panel. Once the bottom panel has been removed, reinstall
the bottom cap. See Figure 7.
NOTE: Units with 1/2 hp blower motor are equipped
with three exible legs and one rigid leg. The rigid leg
is equipped with a shipping bolt and a at white plastic
washer (rather than the rubber mounting grommet used
with a exible mounting leg). See Figure 9. 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 Figure 10.
UNITS WITH 1/2 HP
BLOWER MOTOR
RIDGID LEG
(remove shipping
bolt and washer)
Figure 9.
Blower access panel must be securely in place when
blower and burners are operating. Gas fumes, which
could contain carbon monoxide, can be drawn into
living space, resulting in personal injury or death.
WARNING

507028-03 Page 9 of 66 Issue 1809
Improper installation of the furnace can result in
personal injury or death. Combustion and ue products
must never be allowed to enter the return air system or
air in the living space. Use sheet metal screws and joint
tape to seal return air system to furnace.
In platform installations with furnace return, the furnace
should be sealed airtight to the return air plenum. A door
must never be used as a portion of the return air duct
system. The base must provide a stable support and an
airtight seal to the furnace. Allow absolutely no sagging,
cracks, gaps, etc.
For no reason should return and supply air duct systems
ever be connected to or from other heating devices,
such as a replace or stove, etc. Fire, explosion, carbon
monoxide poisoning, personal injury and/or property
damage could result.
WARNING
Figure 10. Upow Application
Installation Clearances
Top/Plenum 1 in. (25 mm)
* Front 0
Back 0
Sides 0†
Vent 0
Floor 0‡
* Front clearance in alcove installation must be 24 in. (610
mm). Maintain a minimum of 24 in. (610 mm) for front service
access.
† Allow proper clearances to accommodate condensate trap
installation.
‡ For installations on a combustible oor, do not install
the furnace directly on carpeting, tile or other combustible
materials other than wood ooring.
Return Air – Upow Units
Return air can be brought in through the bottom or either
side of the furnace installed in an upow application. If the
furnace is installed on a platform with bottom return, make
an airtight seal between the bottom of the furnace and the
platform to ensure that the furnace operates properly and
safely. The furnace is equipped with a removable bottom
panel to facilitate installation.
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.
Setting an Upow Unit
When the side return air inlets are used in an upow
application, it may be necessary to install shims on the
bottom of the furnace.
Horizontal Applications
The GUH97M furnace can be installed in horizontal
applications with either right or left hand air discharge.
Refer to Figure 11 for clearances in horizontal applications.
Figure 11. Horizontal Application
Installation Clearances
Right-Hand Discharge
Top 0
* Front 0
Back 0
Ends 0
Vent 0
Floor 0‡
* Front clearance in alcove installation must be 24 in. (610
mm). Maintain a minimum of 24 in. (610 mm) for front service
access.
** An 8” service clearance must be maintained below the unit
to provide for servicing of the condensate trap. Unless the
trap is mounted remotely.
‡ For installations on a combustible oor, do not install
the furnace directly on carpeting, tile or other combustible
materials other than wood ooring.

507028-03
Page 10 of 66Issue 1809
Suspended Installation of Horizontal Unit
This furnace may be installed in either an attic or a
crawlspace. Either suspend the furnace from roof rafters or
oor joists, as shown in Figure 12 or install the furnace on
a platform, as shown in Figure 13. A horizontal suspension
kit (51W10) may be ordered or use equivalent.
NOTE: Heavy gauge sheet metal straps may be used to
suspend the unit from roof rafters or ceiling joists. When
straps are used to suspend the unit in this way, support
must be provided for both the ends. The straps must not
interfere with the plenum or exhaust piping installation.
Cooling coils and supply and return air plenums must be
supported separately.
NOTE: When the furnace is installed on a platform in a
crawlspace, it must be elevated enough to avoid water
damage and to allow the evaporator coil to drain.
Figure 12. Typical Horizontal Application
Platform Installation of Horizontal Unit
1. Select location for unit keeping in mind service and
other necessary clearances. See Figure 11.
2. Construct a raised wooden frame and cover frame
with a plywood sheet. If unit is installed above nished
space, fabricate an auxiliary drain pan to be installed
under unit. Set unit in drain pan as shown in Figure
13. Leave 8 inches for service clearance below unit
for condensate trap, unless trap is installed remotely.
3. Provide a service platform in front of unit. When
installing the unit in a crawl space, a proper support
platform may be created using cement blocks.
4. Route auxiliary drain line so that water draining from
this outlet will be easily noticed by the homeowner.
5. If necessary, run the condensate line into a condensate
pump to meet drain line slope requirements. The
pump must be rated for use with condensing furnaces.
Protect the condensate discharge line from the pump
to the outside to avoid freezing.
6. Continue with exhaust, condensate and intake piping
installation according to instructions.
Figure 13.
* Gas Connector may be used for Canadian installation if
acceptable by local authority having jurisdiction.
Return Air - Horizontal Applications
Return air must be brought in through the end of a furnace
installed in the horizontal position. The furnace is equipped
with a removable bottom panel to facilitate installation. See
Figure 7.
Filters
This unit is not equipped with a lter or rack. A eld provided
lter is required for the unit to operate properly. Table 1 lists
recommended lter sizes.
A lter must be in place when the unit is operating!
NOTE: In upow applications where side return air lter is
installed on same side as the condensate trap, make sure
that clearance is maintained to ensure future access to the
lter access panel.
Table 1.
Furnace Cabinet
Width
Minimum Filter Size
Side Return Bottom Return
17-1/2” 16 x 25 x 1 (1) 16 x 25 x 1 (1)
21” 16 x 25 x 1 (1) 20 x 25 x 1 (1)
24-1/2” 16 x 25 x 1 (1) 24 x 25 x 1 (1)

507028-03 Page 11 of 66 Issue 1809
Duct System
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.
NOTE: Operation of this furnace in heating mode (indoor
blower operating at selected heating speed) with an
external static pressure that exceeds 0.8 inches w.c. may
result in erratic limit operation.
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 reected light) of the heat exchanger for leaks after
the furnace is installed. If present, this access panel must
always be in place when the furnace is operating and it
must not allow leaks into or from the supply air duct system.
Return Air Plenum
Return air must not be drawn from a room where this
furnace, or any other gas fueled appliance (i.e., water
heater), or carbon monoxide producing device (i.e., wood
replace) 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
ue products can be pulled back down the vent pipe and
into the room. This reverse ow of the ue 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.
Return air can be brought in through the bottom or either
side of the furnace. If a furnace with bottom return air is
installed on a platform, make an airtight seal between the
bottom of the furnace and the platform to ensure that the
unit operates properly and safely. Use berglass sealing
strips, caulking, or equivalent sealing method between the
plenum and the furnace cabinet to ensure a tight seal. If
a lter is installed, size the return air duct to t the lter
frame.
Pipe and Fittings Specications
All pipe, ttings, 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 owing 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, stratication,
or separation that cannot be removed by stirring. Refer to
Table 2 for approved piping and tting materials.
Table 2.
Piping and Fittings Specications
Schedule 40 PVC (Pipe) D1785
Schedule 40 PVC (Cellular Core Pipe) F891
Schedule 40 PVC (Fittings) D2466
Schedule 40 CPVC (Pipe) F441
Schedule 40 CPVC (Fittings) F438
SDR-21 PVC or SDR-26 PVC (Pipe) D2241
SDR-21 CPVC or SDR-26 CPVC (Pipe) F442
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
Primer & Solvent Cement ASTM
Specication
PVC & CPVC Primer F656
PVC Solvent Cement D2564
CPVC Solvent Cement F493
ABS Solvent Cement D2235
PVC/CPVC/ABS All Purpose Cement For
Fittings & Pipe of the same material
D2564, D2235,
F493
ABS to PVC or CPVC Transition Solvent
Cement D3138
Canada Pipe & Fitting & Solvent
Cement Marking
PVC & CPVC Pipe and Fittings
ULCS636PVC & CPVC Solvent Cement
ABS to PVC or CPVC Transition Cement
Polypropylene Venting System
ULC-S636
PolyPro® by Duravent
InnoFlue® by Centrotherm ULC-S636
ECCO Polypropylene VentTM ULC-S636

507028-03
Page 12 of 66Issue 1809
Solvent cements for plastic pipe are ammable liquids
and should be kept away from all sources of ignition.
Do not use excessive amounts of solvent cement when
making joints. Good ventilation should be maintained to
reduce re hazard and to minimize breathing of solvent
vapors. Avoid contact of cement with skin and eyes.
CAUTION
The exhaust and intake connections are made of PVC.
Use PVC primer and solvent cement when using PVC
vent pipe. When using ABS vent pipe, use transitional
solvent cement to make connections to the PVC ttings
in the unit.
IMPORTANT
Use PVC primer and solvent cement or ABS solvent
cement meeting ASTM specications, refer to Table 2.
As an alternate, use all purpose cement, to bond ABS,
PVC, or CPVC pipe when using ttings and pipe made of
the same materials. Use transition solvent cement when
bonding ABS to either PVC or CPVC.
Low temperature solvent cement is recommended. Metal
or plastic strapping may be used for vent pipe hangers.
Uniformly apply a liberal coat of PVC primer for PVC.
Canadian Applications Only – Pipe, ttings, primer and
solvent cement used to vent (exhaust) this appliance
must be certied to ULCS636 and supplied by a single
manufacturer as part of an approved vent (exhaust)
system. In addition, the rst three feet of vent pipe from the
furnace ue collar must be accessible for inspection.
Table 3 lists the available exhaust termination kits, as well
as vent pipe equivalencies, which must be used when
sizing vent pipe.
Joint Cementing Procedure
All cementing of joints should be done according to the
specications outlined in ASTM D2855.
DANGER OF EXPLOSION!
Fumes from PVC glue may ignite during system check.
Allow fumes to dissipate for at least 5 minutes before
placing unit into operation.
DANGER
1. Measure and cut vent pipe to desired length.
2. Debur and chamfer end of pipe, removing any ridges
or rough edges. If end is not chamfered, edge of pipe
may remove cement from tting socket and result in a
leaking joint.
3. Clean and dry surfaces to be joined.
4. Test t joint and mark depth of tting on outside of pipe.
5. Uniformly apply a liberal coat of PVC primer for PVC
or use a clean dry cloth for ABS to clean inside socket
surface of tting and male end of pipe to depth of tting
socket.
6. Promptly apply solvent cement to end of pipe and
inside socket surface of tting. 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.
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 tting socket. A properly made joint will show a bead
around its entire perimeter. Any gaps may indicate a
defective assembly due to insufcient solvent.
9. Handle joints carefully until completely set.

507028-03 Page 13 of 66 Issue 1809
Venting Practices
Piping Suspension Guidelines
NOTE: Isolate piping at the point where it exits the outside wall or
roof in order to prevent transmission of vibration to the structure.
Wall Thickness Guidelines
Figure 14.
1. In areas where piping penetrates joist or interior walls,
hole must be large enough to allow clearance on all
sides of pipe through center of hole using a hanger.
2. 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 from trap and lines.
Exhaust Piping
(Figure 18 and Figure 19)
3. Route piping to outside of structure. Continue with
installation following instructions given in piping
termination section.
Do not discharge exhaust into an existing stack or
stack that also serves another gas appliance. If vertical
discharge through an existing unused stack is required,
insert PVC pipe inside the stack until the end is even
with the top or outlet end of the metal stack.
CAUTION
The exhaust vent pipe operates under positive pressure
and must be completely sealed to prevent leakage of
combustion products into the living space.
CAUTION
Table 3. Outdoor Termination Kits Usage
GUH97M
VENT
PIPE
DIA.
(in.)
STANDARD CONCENTRIC
Outdoor Exhaust
Accelerator
(Dia. X
Length)
Outdoor
Exhaust
Accelerator
(Dia. X
Length)
Flush
Mount
Kit
1-1/2”
Concentric
Kit
2”
Concentric
Kit
3”
Concentric
Kit
1-1/2” X 12” 2” X 12” 51W11 *
71M80
or
+44W92++
69M29
or
+44W92++
60L46
or 44W93+
070
2YES YES YES
2-1/2 YES YES YES
3YES YES YES
090
2YES YES YES YES
2-1/2 YES YES YES YES
3YES YES YES YES
110
2YES YES YES YES
2-1/2 YES YES YES YES
3YES YES YES YES
135 3 YES YES YES
* Kit 51W11 is provided with a 1-1/2” accelerator which must be for all 2 and 2-1/2” PVC installations.
+ Termination kits 44W92 and 44W93 are approved for use in Canadian installations to meet CSAB149.
++ The 44W92 Concentric kit is provided with a 1-1/2” accelerator Which must be installed on the exhaust outlet when this kit is used
with this furnace.

507028-03
Page 14 of 66Issue 1809
Vent Piping Guidelines
This unit is installed only as a Direct Vent gas central
furnace.
NOTE: In Direct Vent installations, combustion air is taken
from outdoors and ue gases are discharged outdoors.
Intake and exhaust pipe sizing – Size pipe according to
Table 4 and Table 6A through Table 6B. Table 4 lists the
minimum vent pipe lengths permitted. Table 6A through
Table 6B list the maximum pipe lengths permitted.
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 7.
In some applications that permit the use of several different
sizes of vent pipe, a combination vent pipe may be used.
Contact Allied Air Technical Service for more information
concerning sizing of vent systems that include multiple
pipe sizes.
Figure 15.
Exhaust Pipe
Horizontal Application
NOTE: All horizontal runs of exhaust pipe must slope back toward
unit. A minimum of 1/4” (6 mm) drop for each 12” (305 mm) of
horizontal run is mandatory for drainage.
NOTE: Exhaust pipe MUST be glued to furnace exhaust ttings.
NOTE: Exhaust piping should be checked carefully to make sure
there are no sags or low spots.
NOTE: The exhaust collar on all models is sized to
accommodate 2” Schedule 40 vent pipe. In horizontal
applications, transition to exhaust pipe larger than 2” must
be made in vertical runs of the pipe. A 2” elbow must be
added before the pipe is transitioned to any size larger
than 2”. This elbow must be added to the elbow count used
to determine acceptable vent lengths. Contact Allied Air
Technical Service for more information concerning sizing
of vent systems that include multiple pipe sizes.
Do not use screens or perforated metal in exhaust or
intake terminations. Doing so will cause freeze-ups and
may block the terminations.
IMPORTANT
Table 4.
Model Min. Equiv.
Vent Length Example
070, 090
15 ft.*
5ft. plus 2 elbows of 2”, 2-1/2”,
or 3” diameter pipe
110 5 ft. plis elbows of 2-1/2”, 3”
135 5ft. plus 2 elbows of 3”
*Any approved termination may be added to the minimum
equivalent length listed.
Use the steps in Figure 16 to correctly size vent pipe
diameter.
Figure 16.
045, 070,
090, 110
or 135 btuh
Standard or
Concentric?
See Table 3
Intake or
Exhaust?
2”, 2-1/2”
or 3”
Furnace capacity?
1
Which termination?
2
Which needs most
elbows?
3
How many?
4
Desired pipe size?
5
What is the altitude?
6
Use Table 6 to find
max pipe length.
7

507028-03 Page 15 of 66 Issue 1809
General Guidelines for Vent Terminations
In Direct Vent applications, combustion air is taken from
outdoors and the ue gases are discharged to the outdoors.
This gas furnace is classied as a direct vent, Category IV
gas furnace.
In Direct Vent applications, the vent termination is limited
by local building codes. In the absence of local codes,
refer to the current National Fuel Gas Code ANSI Z223-1/
NFPA 54 in U.S.A., and current CSA-B149 Natural Gas
and Propane Installation Codes in Canada for details.
Position termination according to location given in
Figure 20. In addition, position termination so it is free
from any obstructions and 12” above the average snow
accumulation.
At vent termination, care must be taken to maintain
protective coatings over building materials (prolonged
exposure to exhaust condensate can destroy protective
coatings). It is recommended that the exhaust outlet not be
located within 6 feet (1.8m) of a condensing unit because
the condensate can damage the painted coating.
NOTE: See Table 5 for maximum allowed exhaust pipe
length without insulation in unconditioned space during
winter design temperatures below 32°F (0°C). If required,
exhaust pipe should be insulated with 1/2” (13mm)
Armaex or equivalent. In extreme cold climate areas,
3/4” (19mm) Armaex 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 specic
applications.
Do not use screens or perforated metal in exhaust
terminations. Doing so will cause freeze-ups and may
block the terminations.
IMPORTANT
FOR CANADIAN INSTALLATIONS ONLY:
In accordance to CSA International B149 installation
codes, the minimum allowed distance between the
combustion air intake inlet and the exhaust outlet of
other appliances shall not be less than 12 inches (305
mm).
IMPORTANT
Conditioned
Space Unconditioned
Space
Exhaust
Pipe
Intake
Pipe
Conditioned
Space
Pipe Insulation
Figure 17. Insulating Exhaust Pipe in an
Unconditioned Space
Figure 18. Typical Exhaust Pipe Connections and Condensate Trap Installation in Upow Applications

507028-03
Page 16 of 66Issue 1809
Figure 19. Typical Exhaust Pipe Connections and Condensate Trap Installation in Horizontal Air Applications
(Right Hand Discharge Shown)
Table 5.
Maximum Allowable Vent Pipe Length without Insulation in Unconditioned Space for Winter Design Temperatures
Modulating High Efciency Furnace
Winter Design Temperatures1ºF
(ºC)
Vent Pipe
Diameter 070 090 110 135
32 to 21
(0 to -6)
PVC 2PP PVC 2PP PVC 2PP PVC 2PP
2 in. 11 9 14 12 18 15 N/A N/A
2-1/2 in. 7N/A 10 N/A 12 N/A N/A N/A
3 in. N/A N/A 6 6 8 8 13 13
20 to 1
(-7 to -17)
2 in. N/A N/A 6486N/A N/A
2-1/2 in. N/A N/A N/A N/A N/A N/A N/A N/A
3 in. N/A N/A N/A N/A N/A N/A N/A N/A
0 to -20
(-18 to -29)
2 in. N/A N/A N/A N/A N/A N/A N/A N/A
2-1/2 in. N/A N/A N/A N/A N/A N/A N/A N/A
3 in. N/A N/A N/A N/A N/A N/A N/A N/A
1 Refer to 99% Minimum Design Temperature table provided in the current edition of the ASHRAE Fundamentals Handbook.
2 Poly-Propylene vent pipe (PP) by Duravent and Centrotherm
NOTE - Concentric terminations are the equivalent of 5’ and should be considered when measuring pipe length.
NOTE - Maximum uninsulated vent lengths listed may include the termination (vent pipe exterior to the structure ) and cannot exceed
5 linear feet or the maximum allowable intake or exhaust vent length listed in table 5 or 6.
NOTE - If insulation is required in an unconditioned space, it must be located on the pipe closest to the furnace. See Figure 17.

507028-03 Page 17 of 66 Issue 1809
Table 6A.
Maximum Allowable Intake or Exhaust Vent Length (feet)
Standard Termination at Elevation 0 - 4,500 ft
Number of
90° Elbows
Used
2” Pipe 2-1/2” Pipe 3” Pipe
Modal Model Model
70 90 110 135 70 90 110 135 70 90 110 135
1 86 64
n/a n/a
135 88 38
n/a
157 138 113 109
2 81 59 130 83 33 152 133 108 104
3 76 54 125 78 28 147 128 103 99
4 71 49 120 73 23 142 123 98 94
5 66 44 115 68 18 137 118 93 89
6 61 39 110 63 13 132 113 88 84
7 56 34 105 58 8 127 108 83 79
8 51 29 100 53
n/a
122 103 78 74
9 46 24 95 48 117 98 73 69
10 41 19 90 43 112 93 68 64
Standard Termination at Elevation 4,501 - 10,000 ft
Number of
90° Elbows
Used
2” Pipe 2-1/2” Pipe 3” Pipe
Model Model Model
70 90 110 135 70 90 110 135 70 90 110 135
1 61 39
n/a n/a
110 63
n/a n/a
132 113 88 84
2 56 34 105 58 127 108 83 79
3 51 29 100 53 122 103 78 74
4 46 24 95 48 117 98 73 69
5 41 19 90 43 112 93 68 64
6 36 14 85 38 107 88 63 59
7 31 9 80 33 102 83 58 54
8 26
n/a
75 28 97 78 53 49
9 21 70 23 92 73 48 44
10 16 65 18 87 68 43 39
*Size intake and exhaust pipe length separately. Values in table are for intake or exhaust not combined total. Both intake and exhaust
must be same pipe size.

507028-03
Page 18 of 66Issue 1809
Concentric Termination at Elevation 0 - 4,500 ft
Number of
90° Elbows
Used
2" Pipe 2-1/2" Pipe 3" Pipe
Model Model Model
70 90 110 135 70 90 110 135 70 90 110 135
1 78 62
n/a n/a
125 84 34
n/a
141 134 109 100
2 73 57 120 79 29 136 129 104 95
3 68 52 115 74 24 131 124 99 90
4 63 47 110 69 19 126 119 94 85
5 58 42 105 64 14 131 114 89 80
6 53 37 100 59 9 116 109 84 75
7 48 32 95 54
n/a
111 104 79 70
8 43 27 90 49 106 99 74 65
9 38 22 85 44 101 94 69 60
10 33 17 80 39 96 89 64 55
Concentric Termination Elevation 4,501 - 10,000 ft
Number of
90° Elbows
Used
2" Pipe 2-1/2" Pipe 3" Pipe
Model Model Model
70 90 110 135 70 90 110 135 70 90 110 135
1 53 37
n/a n/a
100 59
n/a n/a
116 109 84 75
2 48 32 95 54 111 104 79 70
3 43 27 90 49 106 99 74 65
4 38 22 85 44 101 94 69 60
5 33 17 80 39 96 89 64 55
6 28 12 75 34 91 84 59 50
7 23 7 70 29 86 79 54 45
8 18
n/a
65 24 81 74 49 40
9 13 60 19 76 69 44 35
10 8 55 14 71 64 39 30
*Size intake and exhaust pipe length separately. Values in table are for intake or exhaust not combined total. Both intake and exhaust
must be same pipe size.
Maximum Allowable Intake or Exhaust Vent Length (feet)
Table 6B.

507028-03 Page 19 of 66 Issue 1809
Figure 20.
VENT TERMINATION CLEARANCES
FOR DIRECT VENT INSTALLATIONS IN THE USA AND CANADA
K
D
E
L
B
C
F
G
A
B
J
A
M
I
H
INSIDE CORNER
DETAIL
VENT TERMINAL AIR SUPPLY INLETAREA WHERE TERMINAL
IS NOT PERMITTED
Fixed
Closed
Operable
B
Fixed
Closed
Operable
B
B
A =
B =
C =
D =
E =
F =
G =
H =
I =
J =
K =
L =
M =
US Installations1Canadian Installations2
12 inches (305mm) or 12 in. (305mm)
above average snow accumulation.
12 inches (305mm) or 12 in. (305mm)
above average snow accumulation.
Clearance above grade, veranda,
porch, deck or balcony
Clearance to window or
door that may be opened
6 inches (152mm) for appliances <10,000
pliances > 10,000 Btuh (3kw) and <50,000
pliances > 50,000 Btuh (15kw)
6 inches (152mm) for appliances <10,000
Btuh (3kw), 12 inches (305mm) for
appliances > 10,000 Btuh (3kw) and
<100,000 Btuh (30kw), 36 inches (.9m)
for appliances > 100,000 Btuh (30kw)
Clearance to permanently
closed window
Vertical clearance to ventilated soffit
located above the terminal within a
horizontal distance of 2 feet (610mm)
from the center line of the terminal
Clearance to unventilated soffit
Clearance to outside corner
Clearance to inside corner
tended above meter / regulator assembly
Clearance to service regulator
vent outlet
Clearance to non-mechanical air
pliance
ply inlet
Clearance above paved sidewalk or
paved driveway located on public property
Clearance under veranda, porch, deck or balcony
* 12”
*
*
* 7 feet (2.1m)
3 feet (.9m) within a height 15 feet (4.5m)
above the meter / regulator assembly
3 feet (.9m)
6 inches (152mm) for appliances <10,000
pliances > 10,000 Btuh (3kw) and <50,000
pliances > 50,000 Btuh (15kw)
6 inches (152mm) for appliances <10,000
Btuh (3kw), 12 inches (305mm) for
appliances > 10,000 Btuh (3kw) and
<100,000 Btuh (30kw), 36 inches (.9m)
for appliances > 100,000 Btuh (30kw)
3 feet (.9m) above if within 10 feet
(3m) horizontally
6 feet (1.8m)
7 feet (2.1m)†
12 inches (305mm)‡
1In accordance with the current ANSI Z223.1/NFPA 54 Natural Fuel Gas Code
2In accordance with the current CSA B149.1, Natural Gas and Propane Installation Code *For clearances not specified in ANSI Z223.1/NFPA 54 or CSA
B149.1, clearance will be in accordance with local installation
codes and the requirements of the gas supplier and these
installation instructions.”
† A vent shall not terminate directly above a sidewalk or paved driveway that is located
between two single family dwellings and serves both dwellings.
‡ Permitted only if veranda, porch, deck or balcony is fully open on a minimum of
two sides beneath the floor. Lennox recommends avoiding this location if possible.
* 12”
* Equal to or greater than soffit depth* Equal to or greater than soffit depth
* Equal to or greater than soffit depth * Equal to or greater than soffit depth
* No minimum to outside corner * No minimum to outside corner
3 feet (.9m) within a height 15 feet (4.5m)
above the meter / regulator assembly
3 feet (.9m)
*
*12 inches (305mm)‡
Btuh (3kw), 9 inches (228mm) for ap-
Btuh (15kw), 12 inches (305mm) for ap-
Clearance to each side of center line ex-
Btuh (3kw), 9 inches (228mm) for ap-
Btuh (15kw), 12 inches (305mm) for ap-
supply inlet to building or the com-
bustion air inlet to any other ap-
Clearance to mechanical air sup-

507028-03
Page 20 of 66Issue 1809
* Use wall support every 24” (610 mm). Use two
wall supports if extension is greater than
24” (610 mm) but less than 48” (1219 mm).
NOTE − One wall support must be within 6” (152 mm)
from top of each pipe (intake and exhaust) to prevent
movement in any direction.
NOTE − FIELD−PROVIDED
REDUCER MAY BE
REQUIRED TO ADAPT
LARGER VENT PIPE SIZE
TO TERMINATION
STRAIGHT
APPPLICATION
EXTENDED
APPLICATION
D
B
D
B
A
2” (51mm)
Vent Pipe
3” (76mm)
Vent Pipe
A− Minimum clearance
above grade or average
snow accumulation
B− Maximum horizontal
separation between
intake and exhaust
D− Maximum exhaust
pipe length
E− Maximum wall support
distance from top of each
pipe (intake/exhaust)
12” (305 mm)
12” (305 mm)
12” (305 mm)
6” (152 mm)6” (152 mm)
6” (152 mm)6” (152 mm)
8” (203 mm)8” (203 mm)
20” (508 mm)
6” (152 mm)6” (152 mm)
A
Intake
Elbow
* WALL
SUPPORT
B
A
D
E
B
D
E
A
ALTERNATE TERMINATIONS (TEE & FORTY−FIVE DEGREE ELBOWS ONLY)
C2 -Minimum from end of
exhaust to inlet of intake
C1 -Minimum from end of
exhaust to inlet of intake
FIELD FABRICATED WALL TERMINATION
C1 C2
C1 C2
Front View of
Intake and Exhaust
Intake Exhaust
C
B
1
2
D
A
C3
Intake
Elbow
Exhaust
B
A
D
2” (51MM)
Vent Pipe
3” (76MM)
Vent Pipe
A− Clearance above
grade or average snow
accumulation
B− Horizontal
separation between
intake and exhaust
C− Minimum from
end of exhaust to
inlet of intake
D− Exhaust pipe length
E− Wall support distance
from top of each pipe
(intake/exhaust)
12” (305 mm) Min. 12” (305 mm) Min.
6” (152 mm) Min.
24” (610 mm) Max.
9” (227 mm) Min.
12” (305 mm) Min.
16” (405 mm) Max.
6” (152 mm) Max.
6” (152 mm) Min.
24” (610 mm) Max.
9” (227 mm) Min.
12” (305 mm) Min.
20” (508 mm) Max.
6” (152 mm) Max.
D
C
12”
1
2
E
B
A
1The exhaust termination tee should be connected to the 2” or 3” PVC flue pipe as shown in the illustration.
Do not use an accelerator in applications that include an exhaust termination tee.
The accelerator is not required.
2As required. Flue gas may be acidic and may adversely affect some building materials. If a side wall vent
termination is used and flue gases will impinge on the building materials, a corrosion-resistant shield
(24 inches square) should be used to protect the wall surface. If optional tee is used, the protective shield
is recommended. The shield should be constructed using wood, sheet metal or other suitable material.
All seams, joints, cracks, etc. in affected area, should be sealed using an appropriate sealant.
3Exhaust pipe 45°elbow can be rotated to the side away from the combustion air inlet to direct exhaust
away from adjacent property. The exhaust must never be directed toward the combustion air inlet.
D
C
12”
1
2
E
B
A
Figure 21.