Comfortaire GUH96C User manual

507768-04P Page 1 of 56Issue 1933
INSTALLATION INSTRUCTIONS
GUH96C
Warm Air Gas Furnace
Upow/Horizontal Left and Right Air Discharge
Save these instructions for future reference
(P) 507768-04P
*P507768-04P*
Manufactured By
Comfort-Aire / Century
1900 Wellworth Ave.
Jackson, MI 49203
This manual must be left with the homeowner for future reference.
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.
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
Table of Contents
Unit Dimensions ..........................................................2
Parts Arrangement.......................................................3
Gas Furnace ................................................................4
Shipping and Packing List ...........................................4
Safety Information .......................................................4
General ........................................................................6
Combustion, Dilution & Ventilation Air .........................6
Installation ...................................................................9
Filters .........................................................................13
Duct System ..............................................................13
Venting Practices .......................................................16
Condensate Piping ....................................................34
Gas Piping .................................................................38
Electrical ....................................................................41
Unit Start-Up ..............................................................44
Testing for Proper Venting and Su󰀩cient Combustion
Air for Non-Direct Vent Applications ..........................48
Other Unit Adjustments..............................................48
Blower Performance ..................................................50
Service.......................................................................52
Planned Service ........................................................54
Repair Parts List ........................................................55

507768-04PPage 2 of 56 Issue 1933
Front View
Top View
Side View
3/4
(19)
B
33
(838)
A
1 Bottom Return
Air Opening
9/16
(14)
Air Flow
C
3/4
(19)
14-3/4
(375)
16
(406)
2 Optional
Side Return
Air Filter Kit
(either side)
5/8
(16)
19-7/16 (494)
27-3/4 (705)
6-1/2 (165)
(either side)
14
(356)
Condensate
Trap Connection
(either side)
Electrical Inlet
(either side)
9 (229) Right
6-9/16 (167) Left
Gas Piping Inlet
(either side)
2 (51) (either side)
9/16
(14)
1 (25)
Front Panel
1 Bottom Return
Air Opening
3-1/4
(83)
12-5/8 (321)
(either side)
23
(584)
1Side Return
Air Opening
(either side)
1-15/16 (49)
1-1/2
(38)
23-1/2 (597)
Supply Air
Opening
2 (51)
2-7/8
(73)
Exhaust Air
Outlet
Combustion
Air Intake
2 Optional
Side Return
Air Filter Kit
(either side)
23-3/4 (603)
25 (635)
3-3/8
(86)
D
1NOTE - C*5 (5 Ton) size units installed in upow applications that
require air volumes of 1800 cfm (850 L/s) or greater 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) cleanable air lter. (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.
See “Blower Performance Tables” for additional information.
2 Optional External Side Return Air Filter kit is not for use with
optional Return Air Base.
* Consider sizing requirements for optional IAQ equipment before
cutting side return opening.
Capacity A B C D
in. mm in. mm in. mm in. mm
045-B3
070-B317-1/2 446 16-3/8 416 16 406 7-5/8 194
090-C4
110-C5 21 533 19-7/8 505 19-1/2 495 9-3/8 238
Unit Dimensions

507768-04P Page 3 of 56Issue 1933
Figure 1.
Parts Arrangement

507768-04PPage 4 of 56 Issue 1933
Gas Furnace
The GUH96C Category IV gas furnace is shipped ready for
installation in the upow or horizontal position. The furnace
is shipped with the bottom panel in place. The bottom panel
must be removed if the unit is to be installed in horizontal
or upow applications with bottom return air.
The GUH96C can be installed as either a Direct Vent or a
Non-Direct Vent gas central furnace.
The furnace is equipped for installation in natural gas
applications. A conversion kit (ordered separately) is
required for use in propane/LP gas applications.
NOTE: In Direct Vent installations, combustion air is taken
from outdoors and ue gases are discharged outdoors. In
Non-Direct Vent installations, combustion air is taken from
indoors or ventilated attic or crawlspace and ue gases
are discharged outdoors. See Figure 2 and Figure 3 for
applications involving roof termination.
Figure 2.
Figure 3.
Shipping and Packing List
1 - Assembled Gas Furnace
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 clamp
1 - 2” diameter debris screen
1 - 3/4” Threaded street elbow
NOTE: The required bellows grommet is eld-provided.
See the Gas Piping section for relevant diagrams.
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
di󰀩cult to smell. An LP/Propane leak detector should be
installed in all LP applications.
DANGER
Use only the type of gas approved for use with this furnace.
Refer to unit nameplate.
GUH96C units are CSA International certied to ANSI
Z21.47 and CSA 2.3 standards.
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.
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.

507768-04P Page 5 of 56Issue 1933
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.
Installation Locations
This furnace is CSA International certied for installation
clearances to combustible material as listed on the unit
nameplate and in the table in Figure 13 and Figure 18.
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.
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 within the range specied on the unit nameplate.
Failure to do so may cause erratic limit operation and
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 (Figure 4),
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.
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
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.
Figure 4. Heating Unit Installed Parallel to Air Handler
Unit
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.
This furnace may be installed in alcoves, closets, attics,
basements, garages, and utility rooms in the upow or
horizontal position.
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
Units may be used for heating of buildings or structures
under construction, if the following conditions are met to
ensure proper operation.
DO NOT USE THE UNIT FOR CONSTRUCTION HEAT
UNLESS ALL OF THE FOLLOWING CRITERIA ARE
MET:
a. Furnace must be in its nal location. The vent system
must be permanently installed per these installation
instructions.
b. Furnace must be installed as a two pipe system
and one hundred percent (100%) outdoor air must
be provided for combustion air requirements during
construction.
c. A room thermostat must control the furnace. The use
of xed jumpers that will provide continuous heating is
prohibited.
d. The input rate and temperature rise must be set per
the furnace rating plate.
e. Supply and Return air ducts must be provided and
sealed to the furnace. Return air must be terminated
outside of the space where furnace is installed.

507768-04PPage 6 of 56 Issue 1933
f. Return air temperature range between 60°F (16°C)
and 80°F (27°C) must be maintained.
g. MERV 11 or greater air lters must be installed in
the system and must be regularly inspected and
maintained (e.g., regular static checks and replaced at
end of life) during construction.
h. Blower and vestibule access panels must be in place
on the furnace at all times.
i. The furnace heat exchanger, components, duct
system, and evaporator coils must be thoroughly
cleaned following nal construction clean−up.
j. Air lters must be replaced upon construction
completion.
k. All furnace operating conditions (including ignition,
input rate, temperature rise and venting) must
be veried in accordance with these installation
instructions.
EQUIPMENT MAY EXPERIENCE PREMATURE
COMPONENT FAILURE AS A RESULT OF FAILURE TO
FOLLOW THE ABOVE INSTALLATION INSTRUCTIONS.
FAILURE TO FOLLOW THE ABOVE INSTALLATION
INSTRUCTIONS VOIDS THE MANUFACTURER’S
EQUIPMENT LIMITED WARRANTY. COMFORT-AIRE /
CENTURY DISCLAIMS ALL LIABILITY IN CONNECTION
WITH INSTALLER’S FAILURE TO FOLLOW THE ABOVE
INSTALLATION INSTRUCTIONS.
NOTWITHSTANDING THE FOREGOING, INSTALLER
IS RESPONSIBLE FOR CONFIRMING THAT THE USE
OF CONSTRUCTION HEAT IS CONSISTENT WITH
THE POLICIES AND CODES OF ALL REGULATING
ENTITIES. ALL SUCH POLICIES AND CODES MUST BE
ADHERED TO.
General
These instructions are intended as a general guide and do
not supersede local codes in any way. Consult authorities
having jurisdiction before installation.
In addition to the requirements outlined previously, the
following general recommendations must be considered
when installing 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 non-direct vent
applications, do not install the furnace where drafts
might blow directly into it. This could cause improper
combustion and unsafe operation.
• When the furnace is installed in non-direct vent
applications, do not block the furnace combustion air
opening with clothing, boxes, doors, etc. Air is needed
for proper combustion and safe unit operation.
• When the furnace is installed in an attic or other
insulated space, keep insulation away from the
furnace.
• When the furnace is installed in an unconditioned
space, consider provisions required to prevent freezing
of condensate drain system.
NOTE: The Commonwealth of Massachusetts stipulates
these additional requirements:
• Gas furnaces shall be installed by a licensed plumber
or tter 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 oored.
These units should not be installed in areas normally
subject to freezing temperatures.
CAUTION
Combustion, Dilution & Ventilation Air
If this unit 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 ue gases are discharged outdoors.
In the past, there was no problem in bringing in su󰀩cient
outdoor air for combustion. Inltration 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 replaces 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 down draft can
occur in the furnace vent pipe or chimney. As a result,
combustion gases enter the living space creating a
potentially dangerous situation.
In the absence of local codes concerning air for combustion
and ventilation, use the guidelines and procedures in this
section to install these furnaces to ensure e󰀩cient 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

507768-04P Page 7 of 56Issue 1933
the National Fuel Gas Code (ANSI-Z223.1/NFPA 54). This
reprinted material is not the complete and o󰀩cial position
of ANSI on the referenced subject, which is represented
only by the standard in its entirety.
Insu󰀩cient combustion air can cause headaches,
nausea, dizziness or asphyxiation. It will also cause
excess water in the heat exchanger resulting in rusting
and premature heat exchanger failure. Excessive
exposure to contaminated combustion air will result
in safety and performance related problems. Avoid
exposure to the following substances in the combustion
air supply:
• Permanent wave solutions
• Chlorinated waxes and cleaners
• Chlorine base swimming pool chemicals
• Water softening chemicals
• De-icing salts or chemicals
• Carbon tetrachloride
• Halogen type refrigerants
• Cleaning solvents (such as perchloroethylene)
• Printing inks, paint removers, varnishes, etc.
• Hydrochloric acid
• Cements and glues
• Antistatic fabric softeners for clothes dryers
• Masonry acid washing materials
WARNING
Do not install the furnace in a corrosive or contaminated
atmosphere. Meet all combustion and ventilation air
requirements, as well as all local codes.
CAUTION
In Canada, refer to the CSA B149 Installation codes.
All gas-red appliances require air for the combustion
process. If su󰀩cient combustion air is not available,
the furnace or other appliance will operate ine󰀩ciently
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
replaces, exhaust fans, or clothes dryers are used at the
same time as the furnace, much more air is required to
ensure proper combustion and to prevent a down draft.
Insu󰀩cient air causes incomplete combustion which can
result in carbon monoxide.
In addition to providing combustion air, fresh outdoor air
dilutes contaminants in the indoor air. These contaminants
may include bleaches, adhesives, detergents, solvents
and other contaminants which can corrode furnace
components.
The requirements for providing air for combustion and
ventilation depend largely on whether the furnace is
installed in an unconned or a conned space.
Unconned Space
An unconned 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 unconned, it might be necessary to bring in outdoor air
for combustion if the structure does not provide enough air
by inltration. 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.
Conned Space
A conned space is an area with a volume less than 50
cubic feet (1.42 m³) per 1,000 Btu (.29 kW) per hour of
the combined input rating of all appliances installed in that
space. This denition includes furnace closets or small
equipment rooms.
When the furnace is installed so that supply ducts carry
air circulated by the furnace to areas outside the space
containing the furnace, the return air must be handled by
ducts which are sealed to the furnace casing and which
terminate outside the space containing the furnace. This
is especially important when the furnace is mounted on
a platform in a conned 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
conned space either from inside the building or from
outside.
Air from Inside
If the conned space that houses the furnace adjoins a
space categorized as unconned, air can be brought in
by providing two permanent openings between the two
spaces. Each opening must have a minimum free area of 1
square inch (645 mm²) per 1,000 Btu (.29 kW) per hour of
total input rating of all gas-red equipment in the conned
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 5.

507768-04PPage 8 of 56 Issue 1933
Figure 5. Equipment in Conned Space - All Air From
Inside
Air from Outside
If air from outside is brought in for combustion and
ventilation, the conned space shall be provided with two
permanent openings. One opening shall be within 12” (305
mm) of the top of the enclosure and one within 12” (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 per 4,000 Btu (645
mm² per .59 kW) per hour of the total input rating of all
equipment in the enclosure (see Figure 6 and Figure 7).
It is also permissible to bring in air for combustion from a
ventilated attic (Figure 9) or ventilated crawl space (Figure
10).
Figure 6. Equipment in Conned Space - All Air from
Outside
(Inlet Air from Crawl Space and Outlet Air to
Ventilated Attic)
When communicating with the outdoors through horizontal
ducts, each opening shall have a minimum free area of 1
square inch (645 mm²) per 2,000 Btu (.56 kW) per hour of
the total input rating of all equipment in the enclosure. See
Figure 8.
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 e󰀨ect 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 xed in the open position or interlocked
with the equipment so that they are opened automatically
during equipment operation.
Figure 7. Equipment in Conned Space - All Air from
Outside
(All Air through Ventilated Attic)
Figure 8. Equipment in Conned Space - All Air from
Outside
OUTLET AIR
INLET AIR
NOTE−Each air duct opening shall have a free area of at least one
square inch per 2,000 Btu (645mm2
per .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 communi-
cate directly with the outdoors, each opening shall have a free area
of at least 1 square inch per 4,000 Btu (645mm2
per 1.17kW) per
hour of the total input rating of all other equipment in the enclosure.
ROOF TERMINATED
EXHAUST PIPE
SIDE WALL
TERMINATED
EXHAUST PIPE
(ALTERNATE
LOCATION)
FURNACE

507768-04P Page 9 of 56Issue 1933
If this unit is being installed in an application with
combustion air coming in from a space serviced by an
exhaust fan, power exhaust fan, or other device which
may create a negative pressure in the space, take care
when sizing the inlet air opening. The inlet air opening
must be sized to accommodate the maximum volume
of exhaust air as well as the maximum volume of
combustion air required for all gas appliances serviced
by this space.
WARNING
Ventilation Louvers
Inlet Air
(Minimum 12 in.
(305mm) above
Attic Floor)
Roof Terminated
Exhaust Pipe
Furnace
*Intake Debris
Screen
(Provided)
* See Maximum Vent Lengths table
NOTE-The inlet and outlet air openings shall each have a
free area of at least one square inch per 4,000 Btu (645mm2
per 1.17kW) per hour of the total input rating of all equipment
in the enclosure.
Figure 9. Equipment in Conned Space
(Inlet Air from Ventilated Attic and Outlet Air to
Outside)
Roof Terminated
Exhaust Pipe
Furnace
Ventilation
Louvers
(Crawl Space)
*Intake Debris Screen Provided
Inlet Air
Minimum
12 in. (305mm)
above Crawl
Space Floor
Coupling or
3 in. to 2 in.
Transition
(Field Provided)
* See Maximum Vent Lengths table
NOTE-The inlet and outlet air openings shall each have a
free area of at least one square inch per 4,000 Btu (645mm2
per 1.17kW) per hour of the total input rating of all equipment
in the enclosure.
Figure 10. Equipment in Conned Space
(Inlet Air from Ventilated Crawl Space and Outlet Air
to Outside)
Shipping Bolt Removal
Units with 1/2 hp & 3/4 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 11. 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.
Figure 11.
Units with 1/2 HP & 3/4 HP
Blower Motor
Installation
Setting Equipment
Do not connect the return air ducts to the back of the
furnace. Doing so will adversely a󰀨ect the operation of
the safety control devices, which could result in personal
injury or death.
WARNING
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
Upow Applications
The gas furnaces can be installed as shipped in the upow
position. Refer to Figure 13 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. Tilt the unit slightly (maximum 1/2 in.
from level) from back to front to aid in the draining of the
heat exchanger. See Figure 12.
Allow for clearances to combustible materials as indicated
on the unit nameplate.

507768-04PPage 10 of 56 Issue 1933
Figure 12. Setting Equipment
Tilt the unit slightly (Max. 1/2”) from back to front to aid in the draining of the heat exchanger.
Unit must be level side-to-side in all applications.
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 13. Installation Clearances
Upow Applications
Left Side Right Side
Top
Bottom (Floor)
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.
‡ For installations on a combustible oor, do not install
the furnace directly on carpeting, tile or other combustible
materials other than wood ooring.

507768-04P Page 11 of 56Issue 1933
Return Air Guidelines
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.
Furnace 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 ft.) require either a
return air base or eld-fabricated transition to accommodate
an optional IAQ accessory taller than 14.5”. See Figure 14.
Figure 14. Side Return Air
(with Transition and Filter)
Return
Air
Plenum
Tr ansition
20” X 25” X 1”
(508mm X 635mm X25mm)
Air Filter
Figure 15. Optional Return Air Base
(Upow Applications Only)

507768-04PPage 12 of 56 Issue 1933
Figure 16. Removing the Bottom Panel
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 16.
Horizontal Applications
Do not install the furnace on its front or its back. See
Figure 17.
WARNING
Figure 17.
This furnace can be installed in horizontal applications with
either right or left hand air discharge.
Refer to Figure 18 for clearances in horizontal applications.
Figure 18. Installation Clearances
Horizontal Applications
Bottom (Floor)**
Left End Right End
Air
Flow
Air
Flow
Right-Hand Discharge
Left End Right End
Air
Flow
Air
Flow
Bottom (Floor)**
Left-Hand Discharge
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.
‡ For installations on a combustible oor, do not install
the furnace directly on carpeting, tile or other combustible
materials other than wood ooring.
Suspended Installation of Horizontal Unit
This furnace may be installed in either an attic or a crawl
space. Either suspend the furnace from roof rafters or oor
joists, as shown in Figure 19, or install the furnace on a
platform, as shown in Figure 20. A horizontal suspension
kit (51W10) may be ordered from your distributor or use
equivalent.
Figure 19. Typical Horizontal Application

507768-04P Page 13 of 56Issue 1933
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 or with
the horizontal suspension kit in a crawl space, it must be
elevated enough to avoid water damage, accommodate
drain trap and to allow the evaporator coil to drain.
Platform Installation of Horizontal Unit
1. Select location for unit keeping in mind service and
other necessary clearances. See Figure 18.
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
20. Leave 8 inches for service clearance below unit for
condensate trap.
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 20.
Return Air - Horizontal Applications
Return air may be brought in only 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 16.
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 whenever the unit is operating.
Table 1.
Furnace Cabinet
Width
Filter Size
Side Return Bottom Return
B (17-1/2”)
16 x 25 x 1 (1)
16 x 25 x 1 (1)
C (21”) 20 x 25 x 1 (1)
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: This furnace is not certied for operation in heating
mode (indoor blower operating at selected heating speed)
with an external static pressure which exceeds 0.5 inches
w.c. Operation at these conditions may result in improper
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. The furnace access panel must always
be in place when the furnace is operating and it must not
allow leaks into the supply air duct system.
Return Air Plenum
NOTE: Return air must not be drawn from a room where
this furnace, or any other gas fueled appliance (i.e., water
heater), or carbon monoxide producing device (i.e., wood
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 raw gas or toxic fumes 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

507768-04PPage 14 of 56 Issue 1933
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 & 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
a󰀨ects 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.
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
GUH96C 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 tting 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 during
cooler weather. Metal or plastic strapping may be used for
vent pipe hangers. 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.
Canadian Applications Only
Pipe, ttings, primer and solvent cement used to vent
(exhaust) this appliance must be certied to ULC S636 and
supplied by a single manufacturer as part of an approved
vent (exhaust) system. When bonding the vent system to
the furnace, use ULC S636 approved One-Step Transition
Cement to bond the pipe to the ue collar, or to bond
the 90° elbow or reducing 90° elbow to the ue collar. In
addition, the rst three feet of vent pipe from the furnace
ue collar must be accessible for inspection.
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
SPECIFICATION
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

507768-04P Page 15 of 56Issue 1933
Table 3. Outdoor Termination Kits Usage
Capacity
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" x12" 2" x12" 51W11**
71M80
OR
+44W92++
69M29
OR
+44W92++
60L46
OR
44W93+
045
1 1-1/2 YES YES
2YES YES YES
2-1/2" YES YES YES
3YES YES YES
070
1 1-1/2 YES YES
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
1 2 inch to 1-1/2 inch reducer required, must be eld provided.
* Requires eld provided end installed 1-1/2” exhaust accelerator.
** Kit 51W11 is provided with a 1-1/2” accelerator which must be used for all 45,000 and 70,000 furnace installations. When using
1-1/2 in. piping, the pipe must be transitioned to 2 in. pipe when used with the Flush Mount Kit.
+ Termination kits 44W92, 44W93, 30G28 & 81J20 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 the 45,000 and 70,000 furnaces. When using 1-1/2 in. piping, the pipe must be transitioned to 2 in. pipe when used with the
Concentric Kit.
Joint Cementing Procedure
All cementing of joints should be done according to the
specications outlined in ASTM D 2855.
NOTE: A sheet metal screw may be used to secure the
intake pipe to the connector, if desired. Use a drill or self
tapping screw to make a pilot hole.
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.
NOTE: Time is critical at this stage. Do not allow
primer to dry before applying cement.

507768-04PPage 16 of 56 Issue 1933
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.
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
an improper defective assembly due to insu󰀩cient
solvent.
9. Handle joints carefully until completely set.
Venting Practices
Figure 21.
Removal of the Furnace from Common Vent
In the event that an existing furnace is removed from
a venting system commonly run with separate gas
appliances, the venting system is likely to be too large to
properly vent the remaining attached appliances.
Conduct the following test while each appliance is operating
and the other appliances (which are not operating) remain
connected to the common venting system. If the venting
system has been installed improperly, you must correct the
system as indicated in the general venting requirements
section.
CARBON MONOXIDE POISONING HAZARD
Failure to follow the steps outlined below for each
appliance connected to the venting system being
placed into operation could result in carbon monoxide
poisoning or death.
The following steps shall be followed for each appliance
connected to the venting system being placed into
operation, while all other appliances connected to the
venting system are not in operation.
WARNING
1. Seal any unused openings in the common venting
system.
2. Inspect the venting system for proper size and
horizontal pitch. Determine that there is no blockage,
restriction, leakage, corrosion, or other deciencies
which could cause an unsafe condition.
3. Close all building doors and windows and all doors
between the space in which the appliances remaining
connected to the common venting system are located
and other spaces of the building. Turn ON clothes
dryers and any appliances not connected to the
common venting system. Turn ON any exhaust fans,
such as range hoods and bathroom exhausts, so they
will operate at maximum speed. Do not operate a
summer exhaust fan. Close replace dampers.
4. Follow the lighting instructions. Turn ON the appliance
that is being inspected. Adjust the thermostat so that
the appliance operates continuously.
5. After the main burner has operated for 5 minutes, test
for leaks of ue gases at the draft hood relief opening.
Use the ame of a match or candle.
6. After determining that each appliance connected to
the common venting system is venting properly, (step
3) return all doors, windows, exhaust fans, replace
dampers, and any other gas burning appliances to
their previous mode of operation.
7. If a venting problem is found during any of the
preceding tests, the common venting system must be
modied to correct the problems.
Resize the common venting system to the minimum vent
pipe size determined by using the appropriate tables in
Appendix G. (These are in the current standards of the
National Fuel Gas Code ANSI Z223.1.

507768-04P Page 17 of 56Issue 1933
Figure 22.
CHIMNEY
OR GAS
VENT
(Check sizing
for remaining
appliance)
FURNACE
(Removed from
from common
vent system)
WATER
HEATER
OPENINGS
(To Adjacent
Room)
If this gas 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.
REPLACING FURNACE THAT
WAS PART OF A COMMON
VENT SYSTEM
Exhaust Piping
See Figure 25 and Figure 26
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.
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
Vent Piping Guidelines
This gas furnace 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 ue gases are discharged outdoors.
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 5A through Table 5C. Table 4 lists the
minimum vent pipe lengths permitted. Table 5A through
Table 5C list the maximum pipe lengths permitted.
Regardless of the diameter of pipe used, the standard
roof and wall terminations described in the Exhaust Piping
section 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 which permit the use of several
di󰀨erent sizes of vent pipe, a combination vent pipe may
be used. Contact Comfort-Aire / Century for assistance in
sizing vent pipe in these applications.
NOTE: It is acceptable to use any pipe size which ts
within the guidelines allowed in Table 5A through Table 5C.
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 the
Application Department for more information concerning
sizing of vent systems which include multiple pipe sizes.
Figure 23.

507768-04PPage 18 of 56 Issue 1933
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. Minimum Vent Pipe Lengths
Capacity Min. Vent Length*
045, 070, 090, 110 15 ft or 5 ft plus 2 elbows or
10 ft plus 1 elbow
*Any approved termination may be added to the minimum
length listed.
045, 070,
090, 110
Standard or
Concentric?
See Table 3
Intake or
Exhaust?
1-1/2”, 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 5 to find
max pipe length.
7
Figure 24.

507768-04P Page 19 of 56Issue 1933
Table 5.
Maximum Allowable Intake or Exhaust Vent Length in Feet
Standard Termination at Elevation 0 - 4,500 ft
Number
of 90°
Elbows
Used
1-1/2” Pipe 2” Pipe 2-1/2" Pipe 3" Pipe
Capacity Capacity Capacity Capacity
045 070 090 110 045 070 090 110 045 070 090 110 045 070 090 110
1 20 15
n/a n/a
76 61 39 19 110 95 63 38 132 132 113 113
2 15 10 71 56 34 14 105 90 58 33 127 127 108 108
3 10
n/a
66 51 29 9 100 85 53 28 122 122 103 103
4
n/a
61 46 24
n/a
95 80 48 23 117 117 98 98
5 56 41 19 90 75 43 18 112 112 93 93
6 51 36 14 85 70 38 13 107 107 88 88
7 46 31 9 80 65 33 8 102 102 83 83
8 41 26
n/a
75 60 28
n/a
97 97 78 78
9 36 21 70 55 23 92 92 73 73
10 31 16 65 50 18 87 87 68 68
Standard Termination at Elevation 4,501 - 10,000 ft
Number
of 90°
Elbows
Used
1-1/2” Pipe 2” Pipe 2-1/2" Pipe 3" Pipe
Capacity Capacity Capacity Capacity
045 070 090 110 045 070 090 110 045 070 090 110 045 070 090 110
1 20 15
n/a n/a
76 61 39
n/a
110 95 63 38 132 132 113 113
2 15 10 71 56 34 105 90 58 33 127 127 108 108
3 10
n/a
66 51 29 100 85 53 28 122 122 103 103
4
n/a
61 46 24 95 80 48 23 117 117 98 98
5 56 41 19 90 75 43 18 112 112 93 93
6 51 36 14 85 70 38 13 107 107 88 88
7 46 31 9 80 65 33 8 102 102 83 83
8 41 26
n/a
75 60 28
n/a
97 97 78 78
9 36 21 70 55 23 92 92 73 73
10 31 16 65 50 18 87 87 68 68
*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.
Table 5A.

507768-04PPage 20 of 56 Issue 1933
Maximum Allowable Intake or Exhaust Vent Length in Feet
Concentric Termination at Elevation 0 - 4,500 ft
Number
of 90°
Elbows
Used
1-1/2” Pipe 2” Pipe 2-1/2" Pipe 3" Pipe
Capacity Capacity Capacity Capacity
045 070 090 110 045 070 090 110 045 070 090 110 045 070 090 110
1 15 10
n/a n/a
68 53 37 17 100 85 59 34 116 116 109 109
2 10
n/a
63 48 32 12 95 80 54 29 111 111 104 104
3
n/a
58 43 27 7 90 75 49 24 106 106 99 99
4 53 38 22
n/a
85 70 44 19 101 101 94 94
5 48 33 17 80 65 39 14 96 96 89 89
6 43 28 12 75 60 34
n/a
91 91 84 84
7 38 23 7 70 55 29 86 86 79 79
8 33 18
n/a
65 50 24 81 81 74 74
9 28 13 60 45 19 76 76 69 69
10 23 8 55 40 14 71 71 64 64
Concentric Termination Elevation 4501 - 10,000 ft
Number
of 90°
Elbows
Used
1-1/2” Pipe 2” Pipe 2-1/2" Pipe 3" Pipe
Capacity Capacity Capacity Capacity
045 070 090 110 045 070 090 110 045 070 090 110 045 070 090 110
1 15 10
n/a n/a
68 53 37
n/a
100 85 59 34 116 116 109 109
2 10
n/a
63 48 32 95 80 54 29 111 111 104 104
3
n/a
58 43 27 90 75 49 24 106 106 99 99
4 53 38 22 85 70 44 19 101 101 94 94
5 48 33 17 80 65 39 14 96 96 89 89
6 43 28 12 75 60 34
n/a
91 91 84 84
7 38 23 7 70 55 29 86 86 79 79
8 33 18
n/a
65 50 24 81 81 74 74
9 28 13 60 45 19 76 76 69 69
10 23 8 55 40 14 71 71 64 64
*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.
Table 5B.