Unitary products group G8C 50 User manual

ALL POSITION AUTOMATIC
IGNITION FURNACES
INSTALLATION
INSTRUCTIONS Supersedes: Nothing 650.66-N2V (9/98)
035-15815-401
MODELS: G8C 50 THRU 125 INPUT
& L8C 50 THRU 125 INPUT
TABLE OF CONTENTS
GENERAL INFORMATION......................................1
FURNACE SPECIFICATIONS.................................2
PRE-INSTALLATION INSPECTION........................3
CODE COMPLIANCE ..............................................3
INSTALLATION POSITION......................................3
CONVERSION INFORMATION...............................3
TO CONVERT FROM DOWNFLOW TO UPFLOW
CONFIGURATION ...................................................4
TO CONVERT FROM UPFLOW TO DOWNFLOW
CONFIGURATION ...................................................5
FURNACE LOCATION.............................................5
COMBUSTION AND VENTILATION AIR.................6
FURNACE SIZING AND DUCT SYSTEM DESIGN.8
RETURN AIR AND FILTERS...................................8
GAS PIPING...........................................................10
VENTING (CATEGORY I)......................................12
SIDEWALL VENTING ............................................15
ELECTRICAL WIRING...........................................15
WIRING DIGRAM...................................................17
PRE-OPERATIONAL CHECKS .............................18
SEQUENCE OF OPERATION...............................18
FURNACE OPERATION........................................18
INSTALLATION CHECKS......................................19
SERVICE INSTRUCTIONS....................................21
REPLACEMENT PARTS........................................21
GENERAL INFORMATION
These instructions are for the use of qualified
individual specially trained and experienced in
installation of this type equipment and related
system components.
Installation and service personnel are required
by some states to be licensed. Persons not
qualified shall not install this equipment nor
interpret these instructions
NOTE: The words "shall" or "must" indicate a
requirement which is essential to
satisfactory and safe performance.
The words "should" or "may" indicate a
recommendation or advice which is not
essential and not required but which may be
useful or helpful.
NOTE: After installing the furnace, show the user
how to turn off the electrical power and gas
supply to the furnace. Make sure that the
user understands the importance of
following all safety rules.

2
FURNACE SPECIFICATIONS
BTUH
INPUT
FURNACE
WIDTH
A
BLOWER
WHEEL
SIZE
TEMP.
RISE
°F
CFM
HIGH @
0.5” W.C.
MAX
OUTLET
TEMP. °F
MOTOR
HP VENT DIA. DOWNFLOW SUB-BASE
50,000 17-1/2 10 x 8 30-60 1200 160 1/3 3” 2802-5521
75,000 17-1/2 10 x 8 35-65 1200 165 1/3 4” 2802-5521
75,000 21 10 x 10 30-60 1600 160 1/2 4” 2804-5521
100,000 21 10 x 10 40-70 1600 170 1/2 4” 2804-5521
100,000 24-1/2 (2) 10 x 6 35-65 2000 165 3/4 4” 2805-5521
125,000 24-1/2 (2) 10 x 6 40-70 2000 170 3/4 5” 2805-5521
* All models are supplied with 3” vent connections. An installer supplied transition to 4” or 5” diameter must be
used where necessary.
ABCDEFGHJ
17-1/2
21
24-1/2
16-1/2
20
23-1/2
20-3/8
20-3/8
20-3/8
20
20
20
16
19-1/2
23
14-1/2
18
21-1/2
18-5/8
18-5/8
18-5/8
15-1/8
18-5/8
22-1/8
19
19
19
FIGURE 1 – FURNACE DIMENSIONS AND SPECIFICATION

3
PRE-INSTALLATION INSPECTION
Inspect the shipping container and furnace for any
evidence of shipping damage.
If furnace damage is found, notify freight carrier and
file claim.
NOTE: Some models are equipped with a shipping
strap on the blower motor shaft which
supports the blower motor during shipping.
This strap must be removed before the
furnace is operated for the first time. It can
be removed by removing the two fastening
screws.
CODE COMPLIANCE
The furnaces described in these instructions are
design certified by the American Gas Association to
be in compliance with the latest edition of American
National Standard Z21.47. In Canada, these
furnaces are design certified by the Canadian Gas
Association to be in compliance with the latest
edition of CAN/CGA 2.3.
These furnaces are forced air type and may be
utilized for indoor installation in manufactured
buildings (modular only), or buildings constructed on
site. These furnaces are not certified for installation
in mobile homes, trailers or recreational vehicles.
The installer must conform to all state, local and
provincial building codes when installing these
appliances. In the absence of state, local or provin-
cial codes, these furnaces and related equipment
must be installed in accordance with the latest issue
of the following:
NATIONAL FUEL GAS CODE - ANSI Z223.1
NATIONAL ELECTRICAL CODE, ANSI/NFPA 70.
Applicable codes take precedence over any recom-
mendation made in these instructions.
In Canada, the installer must conform to the
CAN/CGA-B149 Installation Codes, the Canadian
Electrical Code, Part I, CSA C22.1, local plumbing or
waste water codes, and other applicable local
codes.
INSTALLATION POSITION
This furnace may be installed in an upflow, downflow
or horizontal position. Depending on the configura-
tion shipped from the factory, it may be necessary to
convert the furnace from downflow to upflow or from
upflow to downflow configuration. Use conversion
instructions starting on Page 3.
CONVERSION INFORMATION
This furnace may be shipped in either the upflow or
the downflow configuration. To convert from upflow
to downflow or vice-versa it is necessary only to
exchange the top and bottom casing caps and to
rotate the vent blower 180 degrees. Use the step by
step instructions on next page.

4
FIGURE 2 – UPFLOW/HORIZONTAL FIGURE 3 – DOWNFLOW/HORIZONTAL
CONFIGURATION CONFIGURATION
TO CONVERT FROM DOWNFLOW TO
UPFLOW CONFIGURATION
1. Lay the furnace on its back.
2. Remove the front door.
3. Remove the seven sheet metal screws that are
used to fasten the top cap to the casing. Re-
move the top cap and save the screws.
4. Remove the four sheet metal screws that are
used to fasten the bottom cap to the casing.
Remove the bottom cap and save the screws.
5. Unplug the vent blower wires.
6. Disconnect the pressure hose from the vent
blower.
7. Remove the four machine screws that fasten the
vent blower to the vent pan and save the
screws. Leave the gasket in place on the pan.
8. Remove the two extra machine screws in the
vent pan front and save the screws.
9. Rotate the vent blower and transition 180° so
that its outlet points to the outlet air end of the
furnaces as shown in Figure 2.
10. Line up the vent blower mounting holes with the
holes in the vent pan and screw it into place.
Use the same machine screws that held the vent
blower in place previously.
11. Install the two extra machine screws in the two
open holes in the front of the vent pan (See Fig-
ure 2).
12. Plug in the vent motor wires.
13. Plug the pressure hose into the vent blower.
14. Remove the rectangular knockout in the center
of the top cap (See Figure 5.)
15. Install the top cap at the same end of the
furnace as the vent blower, using the sheet
metal screws saved earlier (See Figure 2).
16. Install the bottom cap on the bottom of the
furnace using the sheet metal screws saved
earlier (See Figure 2).
17. The conversion is now complete. The furnace
may now be installed in the upflow position or in
the horizontal position on either side.

5
TO CONVERT FROM UPFLOW TO
DOWNFLOW CONFIGURATION
1. Lay the furnace on its back.
2. Remove the front door.
3. Remove the seven sheet metal screws that are
used to fasten the top cap to the casing.
4. Remove the four sheet metal screws that are
used to fasten the bottom cap to the casing.
Remove the bottom cap and save the screws.
5. Unplug the vent blower wires.
6. Disconnect the pressure hose from the vent
blower.
7. Remove the four machine screws that fasten the
vent blower to the vent pan and save the
screws. Leave the gasket in place on the vent
pan.
8. Remove the two extra machine screws in the
vent pan front and save the screws.
9. Install the cast aluminum transition on the vent
blower, using the three screws supplied on the
vent blower (See Figure 4).
FIGURE 4 – VENT BLOWER
10. Rotate the vent blower 180º so that its outlet
points toward the inlet air end of the furnace
(See Figure 3).
11. Line up the vent blower mounting holes with the
holes in the vent pan and screw it into place.
Use the same machine screws that held the vent
blower in place previously.
12. Install the two extra machine screws in the two
open holes in the front of the vent pan (See Fig-
ure 3).
13. Plug in the vent motor wires.
14. Plug the pressure hose into the vent blower.
15. Remove the round knockout at the right side of
the top cap (See Figure 5).
FIGURE 5 – TOP CAP
16. Install the top cap at the opposite end of furnace
from the vent blower, using the seven sheet
metal screws saved earlier (See Figure 3).
17. Install the bottom cap on the bottom of the
furnace using the sheet metal screws saved
earlier (See Figure 3).
18. The conversion is now complete. The furnace
may now be installed in the downflow position or
in the horizontal position on either side
FURNACE LOCATION
This furnace is design certified for installation as an
upflow, downflow furnace or horizontal furnace on
either side in an alcove, closet, basement, attic,
garage or utility room. It is certified only for use in a
home constructed on-site or a manufactured home
completed at the final site. This furnace is not design
certified to be installed outdoors, in a mobile home,
trailer or recreational vehicle.
The furnace should be located as close to the
chimney or vent as possible and as close to the
center of the warm air distribution system as
possible.
When the furnace is installed in a residential garage
it must be located and installed such that it will be
protected from damage by vehicles. The furnace
must be installed so that the burners are a minimum
of 18" above the floor.
Clearances to Combustible Materials
Proper clearances from the furnace to any combus-
tible materials must be maintained. These required
minimum clearances are shown below and on a
label in the furnace.

6
Minimum Clearances – Upflow
Front: ........................................ 2 inches
Back:.......................................... 0 inches
Sides:......................................... 0 inches
Top............................................. 1 inch
B-1 Vent:.................................... 1 inch
Single-wall Vent:........................ 6 inches
Floor........................................... combustible
Minimum Clearances – Downflow
Front: ......................................... 2 inches
Back:.......................................... 0 inches
Sides:......................................... 0 inches
Top............................................. 1 inch
B-1 Vent:.................................... 1 inch
Single-wall Vent:........................ 6 inches
Floor........................................... non-combustible
For installation on combustible flooring only when
installed on the special downflow sub-base listed in
the Specifications Table on page 2.
Minimum Clearances – Horizontal
Front: ......................................... 2 inches
Back:.......................................... 0 inches
Ends:.......................................... 1 inch
Top............................................. 1 inch
B-1 Vent:.................................... 1 inch
Single-wall Vent:........................ 6 inches
Floor........................................... combustible
When the furnace is installed in the horizontal
position, line contact is permissible. The line formed
by the intersection of the top and sides of the
furnace may be in contact with combustible material.
Do not install the furnace on its back. Doing
so could cause a fire, resulting in damage,
injury or death.
Provide sufficient space around and in front of
the furnace for service and cleaning. Allow a
minimum of 24 inches from the front of the fur-
nace for service clearance. If the furnace is to
be installed in a close clearance closet, the
door should be of adequate size to allow for
removal of the furnace should it become neces-
sary.
Failure to maintain proper clearances to
combustible materials can cause a fire,
which could result in damage, death or per-
sonal injury.
NOTE: This furnace must be installed so the
electrical components are protected from
water.
Installations on Combustible Flooring
This furnace may not be installed directly on com-
bustible materials in the downflow position. It may be
installed directly on floors made of concrete or other-
non-combustible materials. If it is necessary to install
the furnace in the downflow position on a combusti-
ble floor, it is required that a combustible sub-base
be used. The part number of the correct sub-base
accessory is shown in the specification table on
Page 2
COMBUSTION AND VENTILATION AIR
Provide ventilation and combustion air in accor-
dance with section 5.3, Air for Combustion and
Ventilation, of the NATIONAL FUEL GAS CODE,
ANSI Z223.1, or applicable provisions of the local
building codes. In Canada, refer to the latest edition
of the CAN/CGA-B149 Installation Code and local
codes for specifics.
Adequate ventilation and combustion air
must be provided to insure satisfactory and
safe operation of the furnace. Air openings
in front panel and top panel must not be ob-
structed. Failure to observe this recommen-
dation could result in asphyxiation.
Do not store or use halogen-emitting sub-
stances in the vicinity of this appliance.
Such substances include chlorine based
cleaners and swimming pool chemicals, wa-
ter softening chemicals, de-icing salts and
chemicals, cleaning solvents such as car-
bon tetrachloride or perchloroethylene,
halogen type refrigerants, printing inks,
paint and paint removers, varnishes, hydro-
chloric acid, cements and glues, and ma-
sonry acid washing materials. The air used
by the burner for combustion must be free
of halogens to avoid possible corrosion to
the heating surfaces, which could result in
asphyxiation.

7
This furnace is not to be used as a construction
heater to supply heat to an unfinished building
during the finishing phases of construction. This
practice exposes the furnace to abnormally low
return air temperatures, which can cause con-
densation in the furnace or vent leading to pre-
mature failure. This practice also exposes the
furnace to an abnormally corrosive atmosphere
from sources such as paint, varnish and adhe-
sives, which can lead to premature heat ex-
changer or vent failure. The practice also allows
foreign materials such as sawdust or sheet rock
dust to enter the furnace blower, burner, heat
exchanger, motors, and vent system resulting in
shorter life of the furnace. Use of this furnace
as a construction heater will void the war-
ranty.
Installations in a Confined Space
A confined space is defined as a space whose
volume is less than 50 cubic feet per 1000 BTUH of
the total input ratings of all appliances installed in
the space. If the furnace is to be installed in a
confined space such as a small closet or room,
provisions must be made for supplying combustion
and ventilation air to the space surrounding the
furnace. (See Figure 6). This air must come from the
outside or from some larger area in the building
which meets the requirements of an unconfined
space.
Two openings of equal area must be provided; one
starting within twelve inches of the ceiling and one
starting within twelve inches of the floor of the
confined space. The upper opening must always be
above the top of the furnace casing. The lower
opening, if in the sidewall, floor or door, shall be
located below the level of the burner in the furnace.
If all air is from inside building, the total free area of
each opening must be at least one square inch for
each 1,000 BTUH of furnace input but not less than
100 square inches.
If all air is from outdoors, when communicating
directly with the outdoors through vertical ducts, the
total free area of each opening must be at least one
square inch for each 4,000 BTUH of furnace input.
When communicating directly with the outdoors
through horizontal ducts, the total free area of each
duct must be at least one square inch for each 2,000
BTUH of furnace input.
When ducts are used, they must 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 must not be less than three
inches.
Installations in an Unconfined Space
An unconfined space is defined as a space whose
volume is more than 50 cubic feet per 1000 BTUH of
the total input ratings of all appliances installed in
the space. In unconfined spaces in a building of
conventional frame, masonry, or metal construction,
infiltration is normally adequate to provide air for
combustion and ventilation.
In buildings of tight construction, all air must be
obtained from outdoors or from spaces communi-
cating freely with outdoors. A permanent opening or
openings having a total free area of not less than
one square inch for each 5000 BTUH of furnace
input must be provided.
If the furnace is to be installed in a commercial
building, a building with an indoor pool, a laundry
room, hobby or craft room, or chemical storage area,
all air must be brought in from outside as described
above.
Further details on supplying outdoor air for combus-
tion may be obtained from Section 5.3.3 of the
National Fuel Gas Code ANSI Z223.1. In Canada,
refer to the latest edition of the CAN/CGA-B149
Installation Code and local codes for specifics.
When the furnace is installed in an attic or
other insulated space, make sure that all in-
sulation is at least 12” away from furnace
combustion air openings. Failure to do this
could cause asphyxiation or fire.
FIGURE 6 – AIR OPENINGS

8
FURNACE SIZING AND DUCT SYSTEM
DESIGN
The duct system must be installed in conformance
with ASHRAE/NFPA 90, Standard for Installation of
Warm Air Heating and Air Systems and other
applicable local codes. Failure to adhere to proper
duct system design standards can reduce airflow,
resulting in reduced system performance and
possible furnace damage.
Consideration should be given to the heating
capacity required and also to the air quantity (CFM)
required if A/C is to be installed along with the
furnace or at some future time. These factors can be
determined by calculating the heat loss and heat
gain of the home or structure.
If these calculations are not performed and the
furnace is oversized, the following may result:
1. Short cycling of the furnace.
2. Wide temperature fluctuations from the thermo-
stat setting.
3. Reduced overall operating efficiency of the
furnace.
The supply and return duct system must be of
adequate size and designed such that the furnace
will operate within the designed air temperature rise
range and not exceed the maximum designed static
pressure. These values are listed in the table below.
EXT. STATIC IN. W.C.
INPUT BTUH MINIMUM MAXIMUM
50,000 .10 .50
75,000 .12 .50
100,000 .15 .50
125,000 .20 .50
Additional information, values and data necessary
for heat loss, heat gain and duct system design may
be found in the ASHRAE HANDBOOK OF FUNDA-
MENTALS or in other nationally recognized publica-
tions recognized by municipal, state, provincial and
federal code authorities.
If possible, it is recommended that the supply air
duct attached to the furnace be provided with a
removable access panel. The opening should be
accessible when the furnace is installed in service
and should be large enough that smoke or reflected
light may be observed inside the casing to indicate
the presence of leaks in the heat exchanger. The
cover panel for this opening should be attached in
such a manner as to prevent leaks.
A/C Usage Duct Systems
1. When a single (common) duct system is used,
one of the following methods shall be used:
a. A plenum type cooling coil must be installed
on the air discharge side, or
b. A blower-coil type cooling coil must be in-
stalled in parallel with and isolated from the
furnace, or
c. A self-contained A/C unit must be in parallel
with and isolated from the furnace.
Dampers must be installed when coil-blower
or self-contained unit is employed to pre-
vent conditioned cool air from coming in
contact with the heat exchanger to avoid
moisture condensation and rust-out. This
can allow products of combustion to be cir-
culated into the living area by the furnace
blower resulting in possible asphyxiation. If
dampers are of a manually operated type, a
means must be provided to prevent either
the furnace or A/C unit from operating un-
less dampers are in full heat or cool posi-
tion.
If two duct systems are used as could be the case
with a coil-blower or a self-contained A/C unit, the
furnace and A/C unit should be controlled by a
single combination heating and cooling thermostat
which will prevent the furnace and A/C unit from
operating simultaneously.
If a separate heating and separate cooling
thermostat is used, a manually operated
electrical interlock switch must be installed
to prevent simultaneous operation of both
systems and to avoid a possible hazardous
condition due to overheating of the condi-
tioned space.
RETURN AIR AND FILTERS
Return Air Temperature
This furnace design is to be operated in normal
household temperatures. The continuous return air
temperature must not be below 60°F or above 85°F.
Return Air Connection – Upflow
The return air may be brought in through the bottom
of the furnace or through one or both sides of the
furnace casing. The furnace casing may be cut out
so that side return air connections may be used. The
furnace is supplied with flanges on the top of the
furnace to which the return air duct may be fastened.
The casing top is embossed to indicate where to
bend the flanges. If a side return is to be used, cut
out the side of the casing 14" high by 16 1/4" wide
using the lances in the casing side as a guide. DO
NOT CUT THE OPENING LARGER THAN 14"x 16
1/4". It is not permissible to cut out the back of the
furnace.

9
When side return air ducts are used, a solid
metal block-off panel must be used to block the
bottom opening in the furnace. Failure to do so
could cause flue gases to be drawn into the liv-
ing space, which could result in asphyxiation.
The return air ducts to the furnace must have a total
cross sectional area of not less than two square
inches per 1000 BTUH of furnace input rating for
heating operation. If air conditioning is to be installed
with the furnace, or if it may be added at a later time,
larger return air ducts may be required, depending
on the capacity of the air conditioner and the airflow
required. For applications requiring more than 1800
CFM, it will be necessary to use the bottom return,
both side returns or one side plus the bottom return.
Return Air Connection – Downflow
The return air connection to the furnace must be
attached to the top of the furnace. It is not permissi-
ble to cut out the side of the furnace casing for side
return ducts. The furnace is supplied with flanges on
the top of the furnace to which the return air duct
may be fastened. The casing top is embossed to
indicate where to bend the flanges.
The return air ducts to the furnace must have a total
cross sectional area of not less than two square
inches per 1000 BTUH of furnace input rating for
heating operation. If air conditioning is to be installed
with the furnace, or if it may be added at a later time,
larger return air ducts may be required, depending
on the capacity of the air conditioner and the airflow
required. The return air opening in the top of the
furnace is large enough for the largest capacity air
conditioner for which the furnace blower is rated.
Return Air Connection – Horizontal
The return air duct must be connected to the inlet
end of the furnace. It is not permissible to cut out the
side of the furnace casing for side return ducts. The
furnace is supplied with flanges on both ends of the
furnace to which the supply and return air ducts may
be fastened. The casing is embossed on both ends
to indicate where to bend the flanges.
The return air ducts to the furnace must have a total
cross sectional area of not less than two square
inches per 1000 BTUH of furnace input rating for
heating operation. If air conditioning is to be installed
with the furnace, or if it may be added at a later time,
larger return air ducts may be required, depending
on the capacity of the air conditioner and the airflow
required. The return air opening in the top of the
furnace is large enough for the largest capacity air
conditioner for which the furnace blower is rated.
When the furnace is installed so that supply
ducts carry air circulated by the furnace to
areas outside the space containing the fur-
nace, the return air must also be handled by
a duct(s) sealed to the furnace casing and
terminating outside the space containing
the furnace. Failure to do so can result in
asphyxiation.
Filters
Air filters must be used with this furnace. Failure to
do so will cause dirt to accumulate on the furnace
blower motor, blower wheel, heat exchanger and air
conditioning coil, resulting in reduced system
efficiency, erratic control performance and possible
equipment damage.
Air velocity must not exceed 300 feet per minute
through low velocity disposable filters. Air velocity
must not exceed 650 feet per minute through high
velocity cleanable permanent filters. Use of a filter
that is too small will cause static pressure in the duct
system to be too high, which will have an adverse
effect on heating and cooling operation.
Downflow
Filters must be mounted in a location where they are
easily accessible for replacement, either behind a
central return air grille or in a filter box mounted on
top of the furnace as shown in Figure 7. A filter rack
is supplied with the furnace. The table lists the
minimum filter sizes.
FIGURE 7 – DOWNFLOW FILTERS

10
INPUT
BTUH Furnace Width Cleanable Filter Disposable Filter
50,000 17-1/2 14 x 20 (2) 10 x 20
75,000 17-1/2 14 x 20 (2) 14 x 20
75,000 21 16 x 20 (2) 16 x 20
100,000 21 16 x 20 (2) 16 x 20
100,000 24-1/2 20 x 20 (2) 20 x 20
125,000 24-1/2 20 x 20 (2) 20 x 20
Upflow
An appropriately sized permanent cleanable or
disposable filter shall be used. The filter should be
installed in a side return filter rack or, if bottom return
is to be used, in a suitable filter box under the
furnace. Filters must be located external to the
furnace casing (See Figure 8).
FIGURE 8 – UPFLOW FILTERS
Horizontal
An appropriately sized permanent cleanable or
disposable filter shall be used. The filter should be
installed behind a return grille or other location with
easy access for filter change. Locating the filter in a
crawl space, attic or other inaccessible location will
result in filters not being changed as frequently as
recommended.
GAS PIPING
Use only the type of gas for which the fur-
nace is equipped. Using the wrong gas
could create a hazard, resulting in damage,
personal injury or death.
Before installing gas piping, check with local code
authorities for requirements concerning gas piping.
In the absence of local codes, follow the recommen-
dations contained in NATIONAL FUEL GAS CODE
ANSI Z223.1 for gas piping materials, pipe sizing,
and the requirements for installation. In Canada,
refer to the latest edition of the CAN/CGA-B149
Installation Code and local codes for specifics. It is
recommended that a gas cock shutoff valve be
installed in the gas supply line outside the casing,
where it is readily accessible, as close to the furnace
as is practicable, as shown in Figure 9 and 10.
An 1/8 in. NPT (plugged) pressure tap for test gauge
connection must be installed in the gas supply line
immediately upstream from the furnace, if local
authorities do not allow use of the pressure tap in
the gas valve for this purpose.
Install a dirt leg at the bottom of any vertical riser or
drop, as close to the furnace as possible, to collect
moisture and foreign material. Install a ground joint
union just ahead of the gas control valve. A typical
downflow arrangement is shown in Figure 9. A
typical upflow arrangement is shown in Figure 10.
When making the connection at the gas control
valve, use a wrench on the inlet side of the valve to
prevent any possible twisting of the valve body,
which could cause damage and leaks. When making
up pipe joints, use pipe thread compound which is
resistant to natural and LP (propane) gases.

11
FIGURE 9 – DOWNFLOW CONFIGURATION
FIGURE 10 – UPFLOW CONFIGURATION

12
Unless prohibited by local codes, it is permissible to
use a flexible corrugated metal gas connector for the
last section of gas piping connected to the furnace
gas valve. If a flexible connector is used, it must be
certified to be in compliance with ANSI Standard
Z21.24 or, in Canada, with Standard CAN1-6.10.
Following installation of the piping, first ensure that
the gas control lever or switch on the gas valve is in
the off position and then pressurize the system with
gas. Thoroughly check the piping system for leaks.
During pressure testing of the gas supply piping
system, observe the following to avoid fire, ex-
plosion, asphyxiation, or damage to the appli-
ance.
a. If test pressure is less than or equal to 1/2
psig (3.48 kPa)(14" W.C.), isolate the fur-
nace by closing its individual manual shutoff
valve.
b. If test pressure is greater than 1/2 psig (3.48
kPa)(14" W.C.), the furnace and its individ-
ual shutoff valve must be disconnected from
the gas supply system.
Never use an open flame to check for leaks.
Fire or explosion could occur. Since some leak
solutions, including soap and water, may cause
corrosion or stress cracking, the piping must be
rinsed with water after testing unless it has
been determined that the leak solution is non-
corrosive.
The maximum and minimum gas supply pressure
required at the inlet of the gas control valve is shown
on the unit rating plate. When the furnace is in
operation, the inlet pressure must be within the limits
shown.
VENTING (CATEGORY I)
This furnace is a fan-assisted Category I furnace
which operates with a non-positive vent static
pressure and has a flue loss of not less than 17
percent. It may be vented vertically using B-vent
(Category I) or it may be vented horizontally through
a sidewall by using an approved accessory power
venter. For sidewall venting, follow the instructions
accompanying the power venter and the additional
instructions in the section on sidewall venting
beginning on page 16.
The vent installation shall be in accordance with Part
7, Venting of Equipment, of the NATIONAL FUEL
GAS CODE, ANSI Z223.1, or applicable provisions
of the local building codes. In Canada, for more
information regarding vent design and installation,
refer to the latest edition of the CAN/CGA-B149
Installation Code.
1. This furnace must be connected to a factory built
chimney or vent complying with a recognized
standard, or a masonry or concrete chimney
lined with a lining material acceptable to the
authority having jurisdiction.
2. The vent material can be single wall or B-1 (type
B vent with one-inch clearance) for the first five
feet from the furnace. Beyond five feet it must be
B-1 or a permanent, lined chimney.
3. Maintain minimum six-inch clearance to com-
bustible material for single wall vent and one
inch clearance for B-1 vent.
4. When using listed B-1 vent materials and/or a
listed Manufactured chimney, they must be in-
stalled in accordance with the manufacturer’s
installation instructions and the terms of the list-
ing.
5. If horizontal vent pipe is required, it should be as
short as possible and pitch upward toward the
vertical riser or chimney inlet at least 1/4" per
foot to help insure proper venting.
6. Where two or more appliances are connected to
a common vent or flue, use the vent tables in the
venting booklet supplied with this furnace to de-
termine the proper vent connector size.
7. DO NOT USE dampers or restrictors in vent
piping or flue.
8. Vent pipe sections must be securely fastened
together and fastened to the furnace flue collar
using screws where required
9. Joints in the vent pipe must be securely made
and any horizontal run of the vent pipe must be
supported less than one support every three feet
to prevent sagging.
10. This furnace may be common vented with a
water heater or other gas-fired naturally vented
appliance.
This furnace must not be connected into any
portion of a mechanical draft system operating
under positive pressure
This furnace must not be connected to a chim-
ney flue serving a separate appliance designed
to burn solid fuel.

13
Vent System Sizing
Refer to the venting tables in the NATIONAL FUEL
GAS CODE, ANSI Z223.1 for details on proper
sizing of the vent system for this furnace. The
furnace is supplied with a three-inch diameter vent
connection. Some models require four inch or five
inch diameter vent pipe. The specification table on
page 2 lists the proper size of vent connector pipe
for each model of furnace. If a vent pipe of more
than three inch diameter is required for the furnace
being installed, the installer must supply a suitable
transition.
Venting into an Existing Chimney
Whenever possible, B-1 metal pipe should be used
for venting. Where use of an existing chimney is
unavoidable, the following rules must be followed:
1. The masonry chimney must be built and
installed in accordance with nationally recog-
nized building codes or standards and must be
lined with approved fire clay tile flue liners or
other approved liner material that will resist cor-
rosion, softening, or cracking from flue gases.
THIS FURNACE IS NOT TO BE VENTED INTO
AN UNLINED MASONRY CHIMNEY.
2. This furnace may be vented into a fire clay tile
lined masonry chimney only if a source of dilu-
tion air is provided, such as by common venting
with a draft hood equipped water heater. If no
such source of dilution air is available, Type B
vent must be used. The existing chimney may
be used as a chase for the Type B vent.
3. The chimney must extend at least three feet
above the highest point where it passes through
a roof of a building and at least two feet higher
than any portion of the building within a hori-
zontal distance of ten feet.
4. The chimney must extend at least five feet
above the highest equipment draft hood or flue
collar.
Inspection of Existing Chimney
1. Before connecting the vent connector to a
chimney, the chimney passageway must be ex-
amined to ascertain that it is clear and free of
obstructions and must be cleaned if previously
used for venting solid or liquid fuel-burning ap-
pliances or fireplaces.
2. Clean-outs must be examined to determine that
they will remain tightly closed when not in use.
3. When inspection reveals that an existing
chimney is not safe for this application, it must
be rebuilt to conform to nationally recognized
standards, lined or relined with a suitable liner,
or replaced with a suitable vent or chimney.
Venting with Metal Pipe
Type B (double wall) vents must extend in a gener-
ally vertical direction with offsets exceeding 45
degrees, except that one horizontal run may be
allowed. Any angle greater than 45 degrees from the
vertical is considered horizontal. The total horizontal
run of a vent, plus any horizontal vent connector,
must not be greater than 75% of the vertical height
of the vent. A Type B vent must terminate at least
five feet in vertical height above the highest con-
nected equipment draft hood or flue collar.
Vent Connection
The furnace is supplied with a three-inch diameter
vent connection at the vent blower. For installations
where the vent passes in front of the blower com-
partment (downflow and some horizontal), a two-foot
long section of three-inch diameter single-wall vent
pipe should be used to extend the vent outside of
the furnace casing. This section of the vent pipe may
be installer supplied, or factory accessory part
number 2802-312P may be used. If a transition to
type B vent is to be done, the transition should be
outside of the furnace casing. If a transition to a
larger size vent pipe is required, the transition
should be outside of the furnace casing
Vent Connector Sizing
A vent connector must be sized properly for the
equipment connected to it. The furnace is supplied
with a three-inch diameter vent connection. Some
models require four inch or five inch diameter vent
pipe. The specification table on page two lists the
proper size of vent connector pipe for each model of
furnace. If a vent pipe of more than three inch
diameter is required for the furnace being installed,
the installer must supply a suitable transition. Use
the vent tables in the NATIONAL FUEL GAS CODE,
ANSI Z223.1 to determine the proper vent connector
size.
The vent connector must be as short as possible
and the furnace should be located as close as
practicable to the chimney or vent.
The horizontal run of a vent connector must not be
more than 75% of the height of the vertical portion of
the chimney or vent above the connector.
A vent connector must not pass through any ceiling,
floor, firewall, or fire partition. A single-wall metal
pipe vent connector must not pass through any
interior wall.

14
Condensation
These furnaces are not intended to have condensa-
tion occur in the furnace or in the venting system.
Such condensation can cause corrosion and
premature failure of the vent system, leading to
possible asphyxiation. In most cases, condensation
is a result of an oversized vent system. When sizing
the vent system for this furnace, the vent pipe size
should be kept to the minimum allowable according
to the vent tables in the National Fuel Gas Code.
Where local experience indicates that condensation
may be a problem, the following steps should be
taken:
1. Usage of single-wall vent pipe should kept to a
minimum and should never be used in any un-
heated space.
2. As noted above, all masonry chimneys must be
lined with the liner sized no larger than is neces-
sary for the capacity of the attached appliances.
3. If local codes permit, the outside of metal vent
pipe may be insulated with a noncombustible
insulating material.
4. If necessary, the furnace-circulating blower may
be set to a lower speed, which will raise the flue
temperature slightly. However, the temperature
rise across the furnace must not exceed the
maximum listed in the specification table in
these instructions and on the furnace rating
plate.
In certain conditions, condensation in a lined
masonry chimney may be unavoidable. In such
cases, provisions must be made to drain off and
dispose of condensate to avoid damage to the
chimney.
Further Instructions
For more details on venting or other aspects of gas
appliance installation, consult the NATIONAL FUEL
GAS CODE, ANSI Z223.1. In Canada, consult the
CAN/CGA-B149 Installation Code. It is highly
recommended that all gas appliance installers and
servicemen have a copy of this manual.
Replacement of Existing Furnace on
Common Vent System
When this furnace is installed as a replacement for
an old furnace, which is common vented with a
water heater or other gas appliance, and the new
furnace is no longer connected to the common
venting system, the common vent system may be
too large for the appliances remaining on the vent
system after the old furnace is removed. To test for
an oversized vent system, the following steps shall
be followed with each appliance remaining con-
nected to the common venting system placed in
operation, while the other appliances remaining
connected to the common venting system are not in
operation:
1. Seal any unused openings in the common
venting system.
2. Visually inspect the venting system for proper
size and horizontal pitch and determine that
there is no blockage or restriction, leakage, cor-
rosion or other deficiencies which could cause
an unsafe condition.
3. Insofar, as is practical, 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 appliance 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 ex-
haust fan. Close fireplace dampers.
4. Follow the lighting instructions. Place the
appliance being inspected in operation. Adjust
thermostat so appliance will operate continu-
ously.
5. Test for spillage at the draft hood relief opening
after five minutes of main burner operation. Use
the flame of a match or candle, or smoke from a
cigarette, cigar, or pipe.
6. After it has been determined that each appliance
remaining connected to the common venting
system properly vents when tested as outlined
above, return doors, windows, exhaust fans,
fireplace dampers, and any other gas-burning
appliance to their previous condition of use.
7. If improper venting is observed during any of the
above tests, the common venting system must
be corrected. Any changes to the venting sys-
tem must be in accordance with the National
Fuel Gas Code, ANSI Z223.1. In Canada, any
changes to the venting system must be in ac-
cordance with the latest edition of the
CAN/CGA-B149 Installation Codes and applica-
ble local codes. If any portion of the common
venting system must be resized, it should be
resized to approach the minimum size as deter-
mined using the appropriate tables in Appendix
G in the National Fuel Gas Code, ANSI Z223.1
or in Canada, the latest edition of the CAN/CGA-
B149 Installation Code.

15
SIDEWALL VENTING
For applications where vertical Category I venting is
not possible, the only recommended method of
sidewall venting is through the use of an accessory
power venter. Only power venters approved by a
nationally recognized approval agency may be used.
Approved power venters are Tjernlund Models
GPAK-JT or GPAK-1T and Field Controls Models
PVG-2 or SWG-4HD. For installation details, follow
the installation instructions supplied with the power
venter.
When sidewall venting these furnaces with a
power venter, it is required that a barometric
draft damper be installed in the vent near the
furnace. Failure to do so could cause a mal-
function of the furnace resulting in asphyxiation.
NOTE: It is recommended that a post-purge timer
be used. This is a device that keeps the
power venter in operation for a short period
at the end of each burner cycle in order to
clear out all flue gases from the vent.
Manufacturers of power venters also can
supply post-purge timers.
ELECTRICAL WIRING
All internal wiring has been made at the factory.
Field wiring requires only the connection of line
voltage supply wiring and low voltage thermostat
wiring.
Service wiring and control wiring may be brought
into the furnace through either side using the holes
provided.
Refer to the unit rating plate and specification tables
found in these instructions for applicable electrical
characteristics and requirements. A complete wiring
diagram is supplied on page 20.
Service wiring
Field wiring connections should be made inside the
furnace casing and a suitable strain relief should be
used at the point the wires exit the furnace casing. In
order for the electrical controls in the furnace to
operate properly, correct electrical polarity must be
observed. If the furnace does not work on initial
start-up and the diagnostic light on the furnace
control flashes six times, the polarity is reversed.
Field wiring of the unit should conform to local codes
or in the absence of local codes with the National
Electrical Code ANSI/NFPA 70. In Canada, field
wiring of the unit should conform to local codes or in
the absence of local codes with the Canadian
Electrical Code, Part I, and CSA C22.1.
A separate fused circuit from the main electrical
panel should serve only the furnace.
Electrical Grounding
The furnace casing must have an uninterrupted
electrical ground in accordance with the National
Electrical Code ANSI/NFPA 70 or, in Canada, with
the Canadian Electrical Code, Part I, and CSA
C22.1. DO NOT use gas piping as an electrical
ground.
Control Wiring
The thermostat should be installed in accordance
with the manufacturer’s instructions, furnished with
the thermostat, and make connections to the unit as
shown on the unit-wiring diagram. It is recom-
mended that size 18 AWG wire be used.
Heat Anticipator
If the wall thermostat has an adjustable heat
anticipator, the setting should be .48 amps. If any
accessories are to be connected to the furnace, the
heat anticipator setting may change. Use a suitable
ammeter to measure the actual anticipator current.
Accessories
A humidifier or electronic air cleaner may be used
with this furnace. All accessories should be wired
according to the manufacturer’s instructions.
The furnace control board has a terminal marked
EAC, which may be used to power an electronic air
cleaner accessory. This terminal is energized with
115 volts whenever the furnace circulating air blower
is operating in either heating or cooling speed.
The furnace control board has a terminal marked
HUM, which may be used to power an humidifier
accessory. This terminal is energized with 115 volts
whenever the wall thermostat calls for heat.
Make sure that the total load on the furnace trans-
former does not exceed 40 VA, including gas valve,
furnace relays, accessories, and air conditioner
loads.
Do not attempt to wire an electronic air cleaner into
the furnace blower relay. Damage to the furnace
blower motor may result.
Twinning
When two furnaces are installed using the same
duct system, it is very important that the two furnace
circulating air blowers operate simultaneously. If one
blower starts before the second blower, the duct
system will become pressurized with air and the
second blower will be made to turn backwards.
During heating operation, this will cause overheating
of the second furnace, possibly causing an unsafe
condition and damage to the furnace. If twinning of
two furnaces is desired, it is necessary to use the
accessory twinning kit that is designed for use with
these furnaces. The accessory twinning kit is
available from your distributor.

16
Blower Motor Speed Selection
These furnaces are equipped with blowers, which
have multi-speed direct drive motors.
The blower speed selected is dependent upon the
design and static pressure loss of the duct system.
The duct system external static pressure includes
the combined total of the supply and return ducts
and any plenum type air conditioning coil if used.
The furnace must be adjusted to operate at or below
the maximum external static (in. W.C.), and within
the air temperature rise range as shown on the unit
rating plate and in the specification table.
Dependent upon the conditions in a particular
installation, the blower speeds may need to be
changed to give the proper operation on cooling or
heating. The table above shows the proper blower
speed to use for cooling operation.
SHOCK HAZARD – Be sure electrical power to
furnace is turned off before changing motor
speeds.
These leads should be connected in the control box
to either the heating terminal or the cooling terminal,
depending on the airflow desired. The unused motor
speed lead(s) should be connected to the terminals
marked PARK on the blower control board in the
furnace control box.
Motor Terminal Identification
Four-speed motors
White – Common
Black - High
Blue - Medium High
Yellow - Medium Low
Red – Low
Three-speed motors
White - Common
Black - High
Blue – Medium
Red – Low
MOTOR SPEED TAP SELECTION FOR COOLING
COOLING SYSTEM CAPACITY, BTUH
Furnace
Input Blower Wheel 18,000 24,000 30,000 36,000 42,000 48,000 60,000
50,000 10 x 8 Low Med. High
75,000 10 x 8 Low Med. High
75,000 10 x 10 Low Med. Low Med. High High
100,000 10 x 10 Low Med. Low Med. High High
100,000 (2) 10 x 6 Low Med. Low Med. High High
125,000 (2) 10 x 6 Low Med. Low Med. High High
Blower Timings
The electronic furnace control supplied on this
furnace controls the blower delay timings.
The heating on delay, from when the gas valve
opens to when the circulating blower comes on, is
fixed at 30 seconds and is not adjustable.
The heating off delay, from when the gas valve
closes, to when the circulating blower shuts off, is
factory set at 180 seconds. This timing may be
adjusted to 60, 90, 120 or 180 seconds on the
electronic furnace control. The furnace control has
four pins and a small jumper plug, which is used to
adjust the blower off delay. See Figure 11.
FIGURE 11 – BLOWER TIMING CHANGE

17
Diagnostics
The electronic furnace control supplied on this
furnace is equipped with a diagnostic light, which
flashes when there is a service problem with the
furnace. The number of times the light flashes
indicates the location of the problem, as listed
below:
Steady off - Normal operation
One flash - False flame sense - Check for stuck
open gas valve.
Two flashes - Pressure switch stuck closed. Check
for shorted wires, bad pressure switch.
Three flashes - Pressure switch failed to close -
Check vent blower, pressure switch, vent blockage,
disconnected pressure hose.
Four flashes - Limit switch open - Check for open
limit switch, loose connections in limit circuit.
Five flashes - Rollout switch open - Check for open
rollout switches, loose connections in rollout switch
circuit.
Six flashes - One hour pressure switch lockout -
Pressure switch has cycled four times in a single call
for heat - Check for vent blockage, loose connec-
tions in pressure switch circuit.
Seven flashes - One-hour ignition lockout - Burner
failed to light in three tries - Check gas flow, gas
pressure, gas valve operation, flame sensor.
Eight flashes - One-hour ignition lockout - Five
recycles in a single call for heat. Check gas flow, gas
pressure, and gas valve operation, flame sensor.
Nine flashes - Reversed line voltage polarity -
Check incoming power wiring for proper polarity.
Eleven flashes –Jumper wire on control board is
disconnected.
Steady on - Gas valve energized with no call for
heat from thermostat, or, control failure.
WIRING DIGRAM

18
PRE-OPERATIONAL CHECKS
SHOCK HAZARD – Be sure electrical power to
furnace is turned off before performing the pre-
operational checks.
1. Be sure that the furnace is equipped for the type
of gas being supplied to the furnace. See unit
rating plate. If LP (propane) gas is to be used,
make sure that the furnace has been prop-
erly converted.
2. Manually spin circulating air blower wheel to
ensure that it turns freely and does not strike the
blower housing.
3. Was the gas piping tested and/or purged of air
then checked for leaks? See instructions for gas
piping. Even the smallest leak must be elimi-
nated before attempting to light the furnace.
SEQUENCE OF OPERATION
These furnaces are equipped with an electric hot
surface burner ignition system. In response to a call
for heat by the room thermostat, a hot glowing
ignitor lights the burners at the beginning of each
operation cycle. The burners will continue to operate
until the thermostat is satisfied at which time all
burner flame is extinguished. During the off cycle no
gas is consumed. With the room thermostat set
below room temperature and with the electrical
power and gas supply to the furnace on, the normal
sequence of operation is as follows:
1. When the room temperature falls below the
setting of the room thermostat, the thermostat
energizes the furnace control board.
2. When the furnace control board is activated, the
vent blower is turned on. A circuit is also made
through the normally open pressure switch con-
tacts.
3. As the vent blower increases in speed, the
contacts of the pressure switch will close and
complete the electrical circuit to the ignitor.
4. During the next 30 seconds, the vent blower will
bring fresh air into the heat exchanger and the
ignitor will begin to glow. At the end of this pe-
riod, the gas valve will open and the burners will
light.
5. After the burners light, a separate sensor acts as
a flame probe to check for the presence of
flame. As long as a flame is present, the system
will monitor it and hold the gas valve open.
6. If the burners fail to light within 6-8 seconds after
the gas valve opens, the gas valve will close and
the ignitor will be turned off. After a short pause,
the system will recycle and try again for ignition.
If the burners fail to light after three tries, the
ignition system will lock out. The system will re-
main in lockout mode until one hour has passed,
or until the room thermostat is cycled off, then
back on. The furnace will then try for ignition
again.
7. The lapsed time from the moment the room
thermostat closes to when the burners light may
be 30-40 seconds. This delay is caused by the
time required for the vent blower to come to full
speed, the time required for the ignitor to heat
up and the time required for fresh air to be
brought into the heat exchanger.
8. About thirty seconds after the burners have
lighted, the fan switch will close and the furnace
air circulation blower will run.
9. When room thermostat is satisfied the circuit to
the furnace control board is broken. The circuit
to the gas valve is broken and the burners are
extinguished. The vent blower will continue to
run for a few seconds. Then the furnace control
board will keep the circulating blower running for
a period of time to allow additional heat to be
drawn from the heat exchanger.
FURNACE OPERATION
FOR YOUR SAFETY READ BEFORE OPERATING
If you do not follow these instructions ex-
actly, a fire or explosion may result causing
property damage, personal injury or loss of
life.
1. This appliance does not have a pilot. It is
equipped with an ignition device, which auto-
matically lights the burners. DO NOT try to light
the burners by hand.
2. Before operating, smell all around the appliance
area for gas. Be sure to smell next to the floor
because some gas is heavier than air and will
settle on the floor.
WHAT TO DO IF YOU SMELL GAS:
•Don’t try to light any appliance.
•Don’t touch any electric switch; don’t use any
phone in your building.
•Immediately call your gas supplier from a
neighbor's phone. Follow the gas supplier's
instructions.
•If you can not reach your gas supplier, call the
fire department.

19
3. USE ONLY YOUR HAND TO MOVE THE GAS
CONTROL LEVER OR SWITCH. NEVER USE
TOOLS. IF THE LEVER OR SWITCH WILL
NOT MOVE BY HAND, DON’T TRY TO REPAIR
IT, CALL A QUALIFIED SERVICE TECHNI-
CIAN. FORCE OR ATTEMPTED REPAIR MAY
RESULT IN A FIRE OR EXPLOSION.
4. DO NOT USE THIS APPLIANCE IF ANY PART
HAS BEEN UNDER WATER. IMMEDIATELY
CALL A QUALIFIED SERVICE TECHNICIAN
TO INSPECT THE APPLIANCE AND TO RE-
PLACE ANY PART OF THE CONTROL SYS-
TEM AND ANY GAS CONTROL WHICH HAS
BEEN UNDER WATER.
Operating Instructions
1. STOP! Read the safety information listed above.
2. Set the thermostat to the lowest setting, or OFF.
3. Turn off all electric power to the furnace.
4. This appliance does not have a pilot. It is
equipped with an ignition device, which auto-
matically lights the burners. DO NOT try to light
the burners by hand.
5. Remove front door panel.
6. Move gas valve control lever or switch to "OFF".
See Figure 13.
7. Wait five (5) minutes to clear out any gas. Then
smell for gas, including near the floor. If you
smell gas, STOP! Follow "2" in the safety infor-
mation above. If you don’t smell gas, go to the
next step.
8. Move gas control lever or switch to "ON".
9. Replace front door panel.
10. Turn on all electric power to the furnace.
11. Set thermostat to desired setting.
FIGURE 13 – WHITE-RODGERS GAS VALVE
Gas Shutoff
This furnace is equipped with a gas shutoff lever or
switch on the gas valve, which can be used to
prevent gas from flowing to the furnace. Figure 13
shows the location of the shutoff lever or switch. To
turn off gas to the furnace, move the lever or switch
to the "OFF" position.
The furnace installation should also have a manual
shutoff valve in the gas piping to the furnace, similar
to what is shown in Figure 14. To turn off the gas to
the furnace, use a wrench and turn the switch or
lever so that it is pointing 90 degrees from the gas
pipe, as shown in Figure 14.
FIGURE 14 – MANUAL GAS SHUTOFF VALVE
INSTALLATION CHECKS
Checking Gas Input Rate
Natural gas heating values can vary widely. It is
the responsibility of the installer to make sure
that the input rate to the furnace as installed
does not exceed the nameplate rating of the
furnace. Failure to do so can cause heat ex-
changer failure, resulting in injury or death.
The maximum BTUH input capacity for each model
is shown on the furnace rating plate and in the
specification table. This input must not be exceeded.
The input shown may be used in geographic areas
where the elevation is from 0 to 2000 feet. The BTU
input depends on the calorific heating value of the
gas, orifice size, and manifold pressure. Orifice sizes
are based on gas values of 1050 BTU/cu. ft. for
natural gas and 2500 BTU/cu. ft. for LP (propane)
gas. The orifice sizes supplied with the furnace
should provide satisfactory input capacity for
installations in most areas, except at high altitude.
High Altitude Adjustment
In areas above 2000 feet elevation, the furnace BTU
input must be reduced 4% for each 1000 feet of
elevation above sea level. For minor input adjust-
ments, it is permissible to adjust the manifold
pressure at the gas valve pressure regulator. Do not
adjust the manifold pressure more than ±.3" W.C.
from the specified regulator settings (3.5" for natural
gas and 10" for LP (propane gas). In many cases,
adjusting the gas valve manifold pressure may not
be enough to reduce the gas input enough for high
altitudes. In such cases, the gas orifices must be

20
changed to a smaller size. The chart below shows
the proper gas orifice to use at various altitudes for
either natural or LP (propane) gas.
High Altitude Gas Orifices
Altitude above sea level in feet
0-
2000 2000- 4500 4500- 8000 8000- 9000 9000- 10,000
Natural
Gas #42 .093 #43 .089 #44 .086 #45 .082 #46 .081
LP Gas #54
.055 #55 .052 #55 .052 #56 .046 #56 .046
Never attempt to modify this furnace – fire,
explosion, or asphyxiation may result. If
malfunction is apparent, contact a qualified
service agency and/or gas utility for assistance.
How to Determine Gas Input Rate
Where gas is metered, the input rate may be
determined by the following method:
Contact the gas supplier, Public Utility Company or
LP (propane) gas distributor to obtain the calorific
gas value of the gas being used. When checking the
gas input rate, any other gas burning appliances
connected to the same meter should be completely
off. The furnace should be allowed to operate for five
minutes before attempting to check the gas-input
rate.
To check flow rate, observe the one cubic foot dial
on the gas meter and determine the number of
seconds required for the dial hand to complete one
revolution (seconds to flow one cubic foot).
To determine the number of seconds per cubic foot
that is necessary to achieve the correct input rate,
use the following formula: GAS VALUE X 3600 ÷
DESIRED INPUT = SECONDS NEEDED
Example: 1000 BTU gas, furnace input 100,000
BTUH
Seconds for one cubic foot = 1000 X 3600 ÷
100,000 = 36 seconds.
When clocking the meter, if the one cubic foot dial
makes a complete revolution in less time than was
calculated that it should, the furnace is overfired and
should be derated. If it takes more time for the meter
to make one revolution than was calculated, the
furnace is underfired.
The orifice size must be changed to correct an
overfired or underfired condition. If it is determined
that different orifices are needed, please contact
your distributor for assistance in selecting the correct
replacement.
Minor Input Adjustment
The input may be adjusted slightly by adjusting the
pressure in the gas valve in order to change mani-
fold pressure.
To adjust pressure regulator, remove cover screw
(See location on Figure 13) on valve. Turn adjusting
screw counter-clockwise to decrease pressure, turn
clockwise to increase pressure. IN NO CASE
SHOULD THE FINAL MANIFOLD PRESSURE
VARY MORE THAN ±.3" W.C. FROM THE SPECI-
FIED REGULATOR PRESSURE SETTINGS (3.5"
FOR NATURAL GAS AND 10" FOR LP, PROPANE
GAS).
Measuring Air Temperature Rise
For proper furnace operation, the air temperature
rise must be within the range shown on the furnace
rating plate.
Operating the furnace outside of the proper air
temperature rise range may cause poor heating
performance and shorter heat exchanger life.
1. Place thermometer in the supply air plenum
about two feet from the furnace outlet. If an air
conditioning coil is installed, the thermometer
should be placed downstream of the coil. The
thermometer tip should be as near as possible
to the center of the plenum for proper measure-
ment.
2. Place thermometer in return air duct about two
feet from furnace, with the tip of the thermome-
ter as near as possible to the center of the duct.
3. Set thermostat to highest temperature setting
and allow furnace to run for at least five minutes
before checking temperatures.
4. Calculate air temperature rise by subtracting
supply air temperature from the return air tem-
perature.
5. If temperature rise is not within the range shown
on the furnace rating plate, the blower speed
may need to be changed.
6. If the blower speed is changed, recheck the
temperature rise by repeating steps 1 through 4
above.
7. If the air temperature rise is not within the proper
range even after changing blower speeds, check
ductwork design with a qualified heating engi-
neer. It may be necessary to re-size the duct-
work.