Allied Air Enterprises A80UH, 80G1UH User Manual
INSTALLATION INSTRUCTIONS
A80UH & 80G1UH
Warm Air Gas Furnace
Upflow / Horizontal Left and Right Air Discharge
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.
CAUTION
As with any mechanical equipment, personal injury can
result from contact with sharp sheet metal edges. Be
careful when you handle this equipment.
WARNING
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.
TABLE OF CONTENTS
Unit Dimensions ............................................................ 2
A80UH & 80G1UH Parts Arrangement ......................... 3
A80UH & 80G1UH Gas Furnace .................................. 4
Shipping and Packing List ............................................ 4
Safety Information ......................................................... 4
Use of Furnace as a Construction Heater .................... 5
General ......................................................................... 6
Combustion, Dilution, Ventilation Air............................. 6
Setting Equipment ........................................................ 9
Filters .......................................................................... 12
Duct System ................................................................ 12
Venting ........................................................................ 13
*506526-01*
Gas Piping .................................................................. 23
Electrical ..................................................................... 25
Unit Start-Up ............................................................... 29
Heating Sequence of Operation ................................. 30
Gas Pressure Adjustment ........................................... 31
High Altitude ................................................................ 31
Other Unit Adjustments ............................................... 31
Service ........................................................................ 33
Planned Service .......................................................... 36
Integrated Control Diagnostic Codes .......................... 36
Repair Parts List ......................................................... 37
Manufactured By
Allied Air Enterprises, Inc.
A Lennox International, Inc. Company
215 Metropolitan Drive
West Columbia, SC 29170
506526-01 Page 1 of 39Issue 1031
A80UH & 80G1UH Unit Dimensions - inches (mm)
1
NOTE - 20C and 20D size units installed in upflow 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) air filter.
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.
2
Flue outlet may be horizontal but furnace must be vented
vertically.
3
Optional external side return air filter kit cannot be used with
the optional RAB Return Air Base.
* Consider sizing requirements for optional IAQ equipment before
cutting side return opening.
Model
A801UH/80G1UH
045-08
045-12
070-08
070-12
090-12
090-16
110-12
110-16
110-20
135-20
FRONT VIEW
in.
14-1/2
17-1/2
21
24-1/2
SIDE VIEW
A
mm
368
446
533
622
13-3/8
16-3/8
19-7/8
23-3/8
B
in.
mm
340
416
504
546
19-1/2
C
in.
13
16
23
mm
330
406
495
584
in.
4-3/4
6-1/4
9-3/4
D
mm
121
159
8
203
248
506526-01Page 2 of 39 Issue 1031
A80UH & 80G1UH
Expanded View
Figure 1
506526-01 Page 3 of 39Issue 1031
A80UH & 80G1UH Gas Furnace
The A80UH & 80G1UH gas furnace is shipped ready for
installation in the upflow or horizontal right position (for
horizontal left position the combustion air pressure switch
must be moved). 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 upflow applications with
bottom return air.
CAUTION
As with any mechanical equipment, personal injury can
result from contact with sharp sheet metal edges. Be
careful when you handle this equipment.
The furnace is equipped for installation in natural gas
applications. A conversion kit (ordered separately) is required
for use in propane/LP gas applications.
Shipping and Packing List
1 - Assembled Gas Furnace
1 - Bag assembly containing the following:
2 - Screws
3 - Wire nuts
1 - Snap bushing
1 - Snap Plug
1 - Wire tie
1 - Vent warning label
1 - Owner’s manual and warranty card
Check equipment for shipping damage. If you find any
damage, immediately contact the last carrier.
Please refer to specification sheets for available accessories.
Safety Information
Certifications
These units are CSA International certified to ANSI Z21.47.
In the USA, installation of gas furnaces must conform with
local building codes. In the absence of local codes, units
must be installed according to the current National Fuel Gas
Code (ANSI-Z223.1). The National Fuel Gas Code is
available from the following address: American National
Standards Institute, Inc., 11 West 42nd Street, New York,
NY 10036.
Clearances
Adequate clearance must be made around the air openings
into the vestibule area. In order to ensure proper unit
operation, combustion and ventilation air supply must be
provided according to the current National Fuel Gas Code.
Vent installations must be consistent with the venting tables
(in this instruction) and applicable provisions of local building
codes.
This furnace is CSA International certified for installation
clearances to combustible material as listed on the unit
nameplate and in the tables in Figures 8 and 12. Accessibility
and service clearances must take precedence over fire
protection clearances.
DANGER
DANGER OF EXPLOSION!
There are circumstances in which odorant used with
LP/Propane gas can lose its scent. In case of a leak,
LP/Propane gas will settle close to the floor and may be
difficult to smell. An LP/Propane leak detector should
be installed in all LP applications.
WARNING
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.
NOTE: For installation on combustible floors, the furnace
shall not be installed directly on carpeting, tile, or other
combustible material other than wood flooring.
Installed Locations
For installation in a residential garage, the furnace must be
installed so that the burner(s) and the ignition source are
located no less than 18 inches (457 mm) above the floor.
The furnace must be located or protected to avoid physical
damage by vehicles. When a furnace is installed in a public
garage, hangar, or other building that has a hazardous
atmosphere, the furnace must be installed according to
recommended good practice requirements and current
National Fuel Gas Code.
506526-01Page 4 of 39 Issue 1031
Temperature Rise
NOTE: Furnace must be adjusted to obtain a temperature
rise within the range specified on the unit nameplate. Failure
to do so may cause erratic limit operation and may 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. See
Figure 2. With a parallel flow arrangement, a damper (or
other means to control the flow of air) must adequately
pre-vent 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 2.
This furnace may be installed in alcoves, closets, attics,
basements, garages, and utility rooms in the upflow or
horizontal position.
This furnace design has not been CSA certified for
installation in mobile homes, recreational vehicles, or
outdoors.
Use of Furnace as a Construction Heater
Allied Air does not recommended the use of these units as
a construction heater during any phase of construction. Very
low return air temperature, harmful vapors and operation of
the unit with clogged or misplaced filters will damage the
unit.
Units may be used for heating of buildings or structures
under construction, if the following conditions are met:
• The vent system must be permanently installed per these
installation instructions.
• A room thermostat must control the furnace. The use of
fixed jumpers that will provide continuous heating is not
allowed.
Heating Unit Installed Parallel to Air Handler Unit
Heating Unit Installed Upstream of Cooling Unit
Figure 2
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.
• The return air duct must be provided and sealed to the
furnace.
• Return air temperature range between 60°F (16°C) and
80°F (27°C) must be maintained.
• Air filters must be installed in the system and must be
maintained during construction.
• Air filters must be replaced upon construction
completion.
• The input rate and temperature rise must be set per the
furnace rating plate.
• One hundred percent (100%) outdoor air must be
provided for combustion air requirements during
construc-tion. Temporary ducting may supply outdoor
air to the furnace. Do not connect duct directly to the
furnace. Size the temporary duct following these
instructions in section for Combustion, Dilution and
Ventilation Air in a confined space with air from outside.
• The furnace heat exchanger, components, duct system,
air filters and evaporator coils must be thoroughly
cleaned following final construction clean-up.
• All furnace operating conditions (including ignition, input
rate, temperature rise and venting) must be verified
according to these installation instructions.
506526-01 Page 5 of 39Issue 1031
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 chimney or vent termination point.
• Do not install the furnace where drafts might blow directly
into it. This could cause improper combustion.
• Do not block the furnace combustion air openings with
clothing, boxes, doors, etc. Air is needed for proper
combustion and safe unit operation.
• When the furnace is installed in an attic or other insulated
space, keep insulation away from the furnace.
Combustion, Dilution & Ventilation Air
In the past, there was no problem in bringing in sufficient
outdoor air for combustion. Infiltration provided all the air
that was needed. In today’s homes, tight construction
practices make it necessary to bring in air from outside for
combustion. Take into account that exhaust fans, appliance
vents, chimneys, and fireplaces force additional air that could
be used for combustion out of the house. Unless outside
air is brought into the house for combustion, negative
pressure (outside pressure is greater than inside pressure)
will build to the point that a downdraft can occur in the furnace
vent pipe or chimney. As a result, combustion gases enter
the living space creating a potentially dangerous situation.
In the absence of local codes concerning air for combustion
and ventilation, use the guidelines and procedures in this
section to install these furnaces to ensure efficient and safe
operation. You must consider combustion air needs and
requirements for exhaust vents and gas piping.
NOTE: The Commonwealth of Massachusetts stipulates
these additional requirements:
• Gas furnaces shall be installed by a licensed plumber
or fitter only.
• The gas cock must be “T handle” type.
• When a furnace is installed in an attic, the passageway
to and service area surrounding the equipment shall be
floored.
WARNING
Product Contains Fiberglass Wool.
Disturbing the insulation in this product during
installation, maintenance, or repair will expose you to
fiberglass wool. Breathing this may cause lung cancer.
(Fiberglass wool is known to the State of California to
cause cancer.)
Fiberglass wool may also cause respiratory, skin, and
eye irritation.
To reduce exposure to this substance or for further
information, consult material safety data sheets available
from address shown below, or contact your supervisor.
Allied Air Enterprises, Inc.
215 Metropolitan Drive
West Columbia, SC 29170
A portion of this information has been reprinted with
permission from the National Fuel Gas Code (ANSI-Z223.1).
This reprinted material is not the complete and official
position of the ANSI on the referenced subject, which is
represented only by the standard in its entirety.
WARNING
Insufficient combustion air can cause headaches,
nausea, dizziness or asphyxiation. It will also cause
excess water in the heat exchanger resulting in rusting
and premature heat exchanger failure. Excessive
exposure to contaminated combustion air will result in
safety and performance related problems. Avoid
exposure to the following substances in the combustion
air supply:
Permanent wave solutions
Chlorinated waxes and cleaners
Chlorine base swimming pool chemicals
Water softening chemicals
De-icing salts or chemicals
Carbon tetrachloride
Halogen type refrigerants
Cleaning solvents (such as perchloroethylene)
Printing inks, paint removers, varnishes, etc.
Hydrochloric acid
Antistatic fabric softeners for clothes dryers
Masonry acid washing materials
506526-01Page 6 of 39 Issue 1031
All gas fired appliances require air for the combustion
process. If sufficient combustion air is not available, the
furnace or other appliances will operate inefficiently and
unsafely. Enough air must be provided to meet the needs
of all fuel burning appliances and appliances such as exhaust
fans which force air out of the house. When fireplaces,
exhaust fans, or clothes dryers are used at the same time
as the furnace, much more air is necessary to ensure proper
combustion and to prevent a downdraft. Insufficient air
causes incomplete combustion which can result in carbon
monoxide.
In addition to providing combustion air, fresh outdoor air
dilutes contaminants in the indoor air. These contaminants
may include bleaches, adhesives, detergents, solvents and
other contaminants which can corrode furnace components.
Equipment in Confined Space - All Air From Inside
The requirements for providing air for combustion and
ventilation depend largely on whether the furnace is installed
in an unconfined or a confined space.
Unconfined Space
An unconfined space is an area such as a basement or
large equipment room with a volume greater than 50 cubic
feet (1.42 m3) per 1,000 Btu (.29 kW) per hour of the
combined input rating of all appliances installed in that space.
This space also includes adjacent rooms which are not
separated by a door. Though an area may appear to be
unconfined, it might be necessary to bring in outdoor air for
combustion if the structure does not provide enough air by
infiltration. If the furnace is located in a building of tight
construction with weather stripping and caulking around the
windows and doors, follow the procedures in the air from
outside section.
Confined Space
A confined space is an area with a volume less than 50
cubic feet (1.42 m3) per 1,000 Btu (.29 kW) per hour of the
combined input rating of all appliances installed in that space.
This definition includes furnace closets or small equipment
rooms.
When the furnace is installed so that supply ducts carry air
circulated by the furnace to areas outside the space
containing the furnace, the return air must be handled by
ducts which are sealed to the furnace casing and which
terminate outside the space containing the furnace. This is
especially important when the furnace is mounted on a
platform in a confined space such as a closet or small
equipment room. Even a small leak around the base of the
unit at the platform or at the return air duct connection can
cause a potentially dangerous negative pressure condition.
Air for combustion and ventilation can be brought into the
confined space either from inside the building or from outside.
NOTE: Each opening shall have a free area of at least one square
inch per 1,000 Btu (645 mm² per .29 kW) per hour of the total input
rating of all equipment in the enclosure, but not less than 100 square
inches (64546 mm²).
Figure 3
Air from Inside
If the confined space that houses the furnace adjoins a
space categorized as unconfined, air can be brought in by
providing two permanent openings between the two spaces.
Each opening must have a minimum free area of 1 square
inch (645 mm2) per 1,000 Btu (.29 kW) per hour of total
input rating of all gas fired equipment in the confined space.
Each opening must be at least 100 square inches (64516
mm2). One opening shall be within 12 inches (305 mm) of
the top of the enclosure and one opening within 12 inches
(305 mm) of the bottom. See Figure 3.
Air from Outside
If air from outside is brought in for combustion and ventilation,
the confined space must have two permanent openings. One
opening shall be within 12 inches (305 mm) of the top of the
enclosure and one opening within 12 inches (305 mm) of
the bottom. These openings must communicate directly or
by ducts with the outdoors or spaces (crawl or attic) that
freely communicate with the outdoors or indirectly through
vertical ducts. Each opening shall have a minimum free
area of 1 square inch (645 mm2) per 4,000 Btu (1.17 kW)
per hour of total input rating of all equipment in the en-closure.
See Figures 4 and 5. When communicating with the
outdoors through horizontal ducts, each opening shall have
a minimum free area of 1 square inch (645 mm2) per 2,000
Btu (.56 kW) per total input rating of all equipment in the
enclosure. See Figure 6.
506526-01 Page 7 of 39Issue 1031
When ducts are used, they shall be of the same cross
sectional area as the free area of the openings to which
they connect. The minimum dimension of rectangular air
ducts shall be no less than 3 inches (75 mm). In calculating
free area, the blocking effect of louvers, grilles, or screens
must be considered. If the design and free area of protective
covering is not known for calculating the size opening
required, it may be assumed that wood louvers will have 20
to 25 percent free area and metal louvers and grilles will
have 60 to 75 percent free area. Louvers and grilles must
be fixed in the open position or interlocked with the
equipment so that they are opened automatically during
equipment operation.
EQUIPMENT IN CONFINED SPACE - ALL AIR FROM OUTSIDE
(Inlet Air from Crawlspace &
Outlet Air to Ventilated Attic)
EQUIPMENT IN CONFINED SPACE
(ALL AIR FROM OUTSIDE)
NOTE: Each air duct opening shall have a free area of at least one
square inch per 2,000 Btu (645 mm² per .59 kW) per hour of the
total input rating of all equipment in the enclosure. If the equipment
room is located against an outside wall and the air openings
communicate directly with the outdoors, each opening shall have a
free area of at least 1 square inch per 4,000 Btu (645 mm² per 1.17
kW) per hour of the total input rating of all other equipment in the
enclosure.
NOTE: The inlet and outlet air openings shall each have a free area
of at least one square inch per 4,000 Btu (645 mm² per 1.17 kW) per
hour of the total input rating of all equipment in the enclosure.
Figure 4
EQUIPMENT IN CONFINED SPACE - ALL AIR FROM OUTSIDE
(All Air through Ventilated Attic)
Figure 6
NOTE: The inlet and outlet air openings shall each have a free area
of at least one square inch per 4,000 Btu (645 mm² per 1.17 kW) per
hour of the total input rating of all equipment in the enclosure.
Figure 5
506526-01Page 8 of 39 Issue 1031
Setting Equipment
WARNING
Do not install the furnace on its front or its back. Do not
connect the return air ducts to the back of the furnace.
Doing so will adversely affect the operation of the safety
control devices, which could result in personal injury or
death.
The gas furnace can be installed as shipped in either the
upflow position or the horizontal position.
Select a location that allows for the required clearances that
are listed on the unit nameplate. Also consider gas supply
connections, electrical supply, vent connection, and
installation and service clearances [24 inches (610 mm) at
unit front]. The unit must be level.
NOTE: Units with 1/2 hp blower motors are equipped with
three flexible legs and one rigid leg. See Figure 7. The rigid
leg is equipped with a shipping bolt and a flat white plastic
washer (rather than the rubber mounting grommet used with
a flexible mounting leg). The bolt and washer must be
removed before the furnace is placed into operation. After
the bolt and washer have been removed, the rigid leg will
not touch the blower housing.
Upflow Applications
Allow for clearances to combustible materials as indicated
on the unit nameplate. Minimum clearances for closet or
alcove installations are shown in Figure 8.
Upflow Application Installation Clearances
Figure 7
Units with 1/2 HP
Blower Motor.
* Front clearance In alcove Installation must be 24 in. (610 mm).
Maintain a minimum of 24 in. (610 mm) for front service access.
‡ For installation on a combustible floor, do not install the furnace
directly on carpeting, tile or other combustible materials other than
wood flooring.
† Left side requires 3 inches if a single wall vent is used on 14-1/2
inch cabinets.
Figure 8
506526-01 Page 9 of 39Issue 1031
Return Air - Upflow Applications
Return air can be brought in through the bottom or either
side of the furnace installed in an upflow application. If the
furnace is installed on a platform with bottom return, make
an airtight seal between the bottom of the furnace and the
platform to ensure that the furnace operates properly and
safely. The furnace is equipped with a removable bottom
panel to facilitate installation.
Markings are provided on both sides of the furnace cabinet
for installations that require side return air. Cut the furnace
cabinet at the maximum dimensions shown on page 2.
NOTE: 20C and 20D units that require air volumes over
1800 cfm (850 L/s) must have one of the following:
1. Single side return air with transition to
accommodate 20 x 25 x 1 in. (508 x 635 x 25 mm)
cleanable air filter. (Required to maintain proper air
velocity.) See Figure 9.
2. Single side return air with optional return airbase.
See Figure 10.
3. Bottom return air.
4. Return air from both sides.
5. Bottom and one side return air.
Single Side Return Air
(with transition and filter)
Figure 9
Optional Return Air Base
(Upflow Applications Only - For use with A, B, C and D cabinets))
FRONT VIEW
NOTE: Optional Side Return Air Filter Kits are not for use with Return Air Base.
1 Both the unit return air opening and the base return air opening must be covered by a single plenum or IAQ cabinet.
Minimum unit side return air opening dimensions for units requiring 1800 cfm or more of air (W x H): 23 x 11 in. (584 x 279 mm).
The opening can be cut as needed to accommodate plenum or IAQ cabinet while maintaining dimensions shown.
Side return air openings must be cut in the field. There are cutting guides stenciled on the cabinet for the side return air opening.
The size of the opening must not extend beyond the markings on the furnace cabinet.
² To minimize pressure drop, the largest opening height possible (up to 14 inches) is preferred.
Figure 10
506526-01Page 10 of 39 Issue 1031
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 11.
Removing the Bottom Panel
Horizontal Applications
The furnace can be installed in horizontal applications. Order
horizontal suspension kit (51W10) from Allied Air, or use
equivalent suspension method.
Allow for clearances to combustible materials as indicated
on the unit nameplate. Minimum clearances for closet or
alcove installations are shown in Figure 12.
This furnace may be installed in either an attic or a crawl
space. Either suspend the furnace from roof rafters or floor
joists, as shown in Figure 13, or install the furnace on a
platform, as shown in Figure 14.
Typical Horizontal Application
Unit Suspended in Attic or Crawlspace
Figure 11
Horizontal Application
Installatioin clearances
* Front clearance in alcove installation must be 24 in. (610 mm).
Maintain a minimum of 21 in. (610 mm) for front service access.
‡ For installations on a combustible floor, do not install the furnace
directly on carpeting, tile or other combustible materials other than
wood flooring.
Figure 13
NOTE: Heavy gauge perforated sheet metal straps may
be used to suspend the unit from roof rafters or ceiling joists.
When straps are used to suspend the unit in this way, support
must be provided for both the ends. The straps must not
interfere with the plenum or exhaust piping installation.
Cooling coils and supply and return air plenums must
be supported separately.
NOTE: When the furnace is installed on a platform in a
crawlspace, it must be elevated enough to avoid water
damage and to allow the evaporator coil to drain.
Return Air - Horizontal Applications
Return air must be brought in through the end of a furnace
installed in a horizontal application. The furnace is equipped
with a removable bottom panel to facilitate installation. See
Figure 11.
Figure 12
506526-01 Page 11 of 39Issue 1031
Horizontal Application
Unit installed on Platform
Figure 14
WARNING
Improper installation of the furnace can result in personal
injury or death. Combustion and flue products must
never be allowed to enter the return air system or the
living space. Use screws and joint tape to seal the return
air system to the furnace.
In platform installations with bottom return air, the furnace
should be sealed airtight to the return air plenum. A
door must never be used as a portion of the return air
duct system. The base must provide a stable support
and an airtight seal to the furnace. Allow absolutely no
sagging, cracks, gaps, etc..
Table 1
Duct System
Use industry approved standards (such as those published
by Air Conditioning Contractors of America or American
Society of Heating, Refrigerating and Air Conditioning
Engineers) to size and install the supply and return air duct
system. This will result in a quiet and low static system that
has uniform air distribution.
NOTE: Do not operate the furnace in the heating mode
with an external static pressure that exceeds 0.8 inches w.c.
Higher external static pressures may cause erratic limit
operation.
Supply Air Plenum
If the furnace is installed without a cooling coil, a removable
access panel must be installed in the supply air duct. The
access panel should be large enough to permit inspection
(either by smoke or reflected light) of the heat exchanger
for leaks after the furnace is installed. The furnace access
panel must always be in place when the furnace is operating
and it must not allow leaks into the supply air duct system.
Return Air Plenum
The return and supply air duct systems must never be
connected to or from other heating devices such as a
fireplace or stove, etc.. Fire, explosion, carbon
monoxide poisoning, personal injury and/or property
damage could result.
WARNING
The inner blower panel must be securely in place when
the blower and burners are operating. Gas fumes,
which could contain carbon monoxide, can be drawn
into living space resulting in personal injury or death.
Filters
This unit is not equipped with a filter or rack. A field provided
high velocity filter is required for the unit to operate properly.
Table 1 lists recommended filter sizes.
A filter must be in place any time the unit is operating.
NOTE: Return air must not be drawn from a room where
this furnace, or any other gas fueled appliance (i.e., water
heater), or carbon monoxide producing device (i.e., wood
fireplace) is installed.
When return air is drawn from a room, a negative pressure
is created in the room. If a gas appliance is operating in a
room with negative pressure, the flue products can be pulled
back down the vent pipe and into the room. This reverse
flow of the flue gas may result in incomplete combustion
and the formation of carbon monoxide gas. This toxic gas
might then be distributed throughout the house by the furnace
duct system.
In upflow applications, the return air can be brought in through
the bottom or either side of the furnace. If a furnace with
bottom return air is installed on a platform, make an airtight
seal between the bottom of the furnace and the platform to
ensure that the unit operates properly and safely. Use
fiberglass sealing strips, caulking, or equivalent sealing
method between the plenum and the furnace cabinet to
ensure a tight seal. If a filter is installed, size the return air
duct to fit the filter frame.
506526-01Page 12 of 39 Issue 1031
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