Goodman GMN SERIES Manual

INSTALLATION
& OPERATING
INSTRUCTIONS
for GMN SERIES
GAS FURNACES
(PATENT PENDING)
Goodman Manufacturing Company, L.P.
IO-554 1501 Seamist, Houston, Texas 77008 11/93

INDEX
Page
Typical Upflow Installation 3
Typical Downflow Installation 3
General Information 4
Clearances - Accessibility 4
Changing Orientation of Vent Blower 5
Converting Furnace To Downflow Configuration 5
Combustion/Ventilation Air Supply 5 - 6
Venting 6 - 7
Converting Furnace To Propane 8
Gas Supply and Piping 8
Circulating Supply Air and Return Air 8 - 9
Electrical Connection 9
Thermostat Location and Low Voltage Connections 9 - 10
To Rate Furnace 10
Main Burner Adjustment 11
Safety Controls Functions & Check Out Procedures 11
Fan Control/Ignition Module & Circulating Air Filters 11
Temperature Rise & Motor Lubrication and Maintenance 12
System Operation Information and Primary\Secondary
Heat Exchanger Cleaning 12
Lighting Instructions 13
Sequence of Operation 13
Normal Operation 14
Wiring Diagram 15
2

3
TYPICAL UPFLOW INSTALLATION
GAS PIPING
See pages 13 & 14
ELECTRICAL
CONNECTIONS
See page 16
RETURN AIR
See pages 14 & 15
VENTING
See pages 10 - 12 and
Venting Tables
SUPPLY AIR
See pages 14 & 15
VENTILATION /
COMBUSTION AIR
See pages 8 & 9

4
TYPICAL DOWN FLOW INSTALLATION
RETURN AIR
See pages 14 & 15
VENTING
See pages 10 - 12
and Venting Tables
ELECTRICAL
CONNECTIONS
See page 16
SPECIAL BASE
See page 6
SUPPLY AIR
See pages 14 & 15
GAS SUPPLY
See pages 13 & 14
COMBUSTION /
VENTILATION AIR
See pages 8 & 9

5
CAUTION: TO ENSURE PROPER INSTALLATION AND OPERATION OF THIS PRODUCT, COMPLETELY READ AND
UNDERSTAND THESE INSTRUCTIONS PRIOR TO ATTEMPTING TO ASSEMBLE, INSTALL, MAINTAIN OR REPAIR.
GENERAL INFORMATION
INSTALLATION: In the USA this furnace should be installed in accordance with the latest edition of the American National
Standard Z223.1 booklet entitled “National Fuel Gas Code” (NFPA 54), and the requirements or codes of the local utility or
other authority having jurisdiction. In Canada this furnace must be installed in accordance with the current CAN/CGA-B149.1
& .2 Gas Installation Codes, local plumbing or waste water codes, and other applicable codes.
Additional helpful publication available from the “National Fire Association” are: NFPA 90A - Installation of Air Conditioning
and Ventilating System, NFGA 90B - Warm Air Heating and Air Conditioning System.
These publications are available from:
National Fire Protection Association, Inc.
Batterymarch Park
Quincy, MA 02269
LOCATION: Do not install this furnace in a mobile home. The furnace designed only for installation in buildings constructed
on-site. This heating unit should be centralized with respect to the heat distribution system as much as possible. When
installed in a utility room, the door should be wide enough to allow the largest part of the furnace to enter, or to permit the
replacement of another appliance, such as a water heater. This furnace is designed to be installed indoors only. Do not
install outdoors. This furnace shall be installed in a manner so that it is protected from water. Do not install this unit in a
horizontal configuration.
CLEARANCE - ACCESSIBILITY
The furnaces covered in this manual are certified by ETL and WARNOCK HERSEY Laboratories for clearances to
combustible materials (in inches) as shown below.
It is recommended that a least 24" clearance be allowed in front of all furnaces for proper servicing.
RECOMMENDED
1"

ACCESSIBILITY CLEARANCE, WHERE GREATER, SHOULD TAKE PRECEDENCE OVER MINIMUM FIRE PROTEC-
TION CLEARANCE.
A gas-fired furnace for installation in a residential garage must be installed so that the burner(s) and the ignition source are
located not less than 18" above the floor and is located or protected to avoid physical damage by vehicles.
An upflow gas-fired furnace must not be installed directly on carpeting, tile or other combustible material other than wood
flooring.
WARNING: COMBUSTIBLE MATERIAL MUST NOT BE PLACED ON OR AGAINST THE FURNACE JACKET.
THE AREA AROUND THE FURNACE MUST BE KEPT CLEAR AND FREE OF ALL COMBUSTIBLE
MATERIAL INCLUDING GASOLINE AND OTHER FLAMMABLE VAPORS AND LIQUIDS. THE USER
SHOULD BE CAUTIONED THAT THE FURNACE AREA MUST NOT BE USED AS A BROOM CLOSET
OR FOR ANY OTHER STORAGE PURPOSE.
UPFLOW FURNACES ONLY
WARNING: IMPORTANT NOTICE. A SOLID METAL BASE PLATE IS SUPPLIED WITH THIS FURNACE AND MUST
BE IN PLACE WHEN THE FURNACE IS INSTALLED WITH SIDE AIR RETURN DUCTS. FAILURE TO
LEAVE THIS BASE PLATE INSTALLED COULD CAUSE PRODUCTS OF COMBUSTION TO BE
CIRCULATED INTO LIVING SPACE AND CREATE POTENTIALLY HAZARDOUS CONDITIONS,
INCLUDING CARBON MONOXIDE POISONING. REFER TO SECTION ON “CIRCULATING AIR
SUPPLY” FOR RETURN AIR DUCTWORK INSTRUCTIONS.
DOWNFLOW FURNACES ONLY
Downflow furnaces are not certified for use on combustible flooring unless a special combustible floor base is installed. See
table below for details:
Furnace Width Special Base Part Number
14" SBM-14
17 1/2" SBM-17
21" SBM-21
24 1/2" SBM-24
Before proceeding with the remaining installation, check the following:
1.) Correct clearances from combustible material
2.) Adequate accessibility for servicing
3.) Flooring is not carpet, tile or any other combustible material (except wood)
4.) In a garage, the furnace has been adequately elevated
5.) Furnace area is free of flammable materials and vapors such as gasoline
6.) The metal base plate used on upflow furnaces with side air returns is in position.
7.) A special base has been installed on downflow furnaces if they are installed on combustible flooring.
6

7
6
CHANGING ORIENTATION OF VENT BLOWER
1
2
This furnace is shipped from the factory in the upflow
configuration with the vent connection on the left side. It can
be easily converted to right side venting following the
instructions below :
Electrical and Gas Supply must be "OFF" before attempting
any service.
Step 1
Disconnect the Power Supply.
Step 2
Rotate the quarter turn fasteners (items 1) 90 degrees to
release the Control Access Panel (item 2)
Step 3
Disconnect the Power wires to Vent Blower, Stack Overtemp
wires, and Pressure Switch tube leading to Vent Blower.
Step 4
Remove the three screws (item 3) which secure the Vent
Blower (item 4) to the Heat Shield (item 5) on illustration.
Step 5
Rotate Vent Blower 180 degrees counter clockwise. (WARN-
ING) Make sure that the O-Ring, and Restrictor Plate (if
used), (items 6) are located properly.
Step 6
Make sure the Vent Blower is properly seated against the O-
Ringand Vent Blower legs are aligned with the holes in Heat
Shield.
Step 7
Tighten the three screws (item 3), reconnect wiring to Vent
Blower and Stack Overtemp Switch. Reconnect tube from
Pressure Switch to Vent Blower.
4
5
3
5
4

8
CONVERTING FURNACE TO DOWNFLOW CONFIGURATION
8
7
5
Step 8
Replace Control Access Panel and reconnect Power Sup-
ply.
Step 1
Disconnect the Power Supply
Step 2
Rotate the quarter turn fasteners (items 1, page 7) 90° to
release the Control Access Panel (item 2, page 7).
Step 3
Relocate Pressure Switch (item 7), from Heat Shield (item
5) to Blower Deck (item 8) for Downflow conversion.
A leading cause of unsatisfactory or dangerous performance
is due to inadequate provisions for combustion and ventila-
tion air. The following (Figure 1 through Figure 3.) outline the
minimum combustion/ventilation air this furnace and any
additional gas fired equipment require when installed in a
confined area. It is important that provisions be made for
adequate combustion and ventilation air (in accordance with
section 5.3, Air for Combustion and Ventilation, of the
National Fuel Gas Code, ANSI Z223.1, or applicable local
building codes). In Canada use the current CAN/CGA-
B149.1 & 2 Gas Installation Codes.
It is important that the following be observed when installing
the combustion/ventilation air supplies for your system.
COMBUSTION / VENTILATION AIR SUPPLY
Fig. 1
Fig. 3
Fig. 2

9
1.) The passageways that supply combustion/ventilation air must not be obstructed to prevent flow of air to the mechanical
room. Extra care is to be used to prevent blockage of the ducts due to insulation, as may occur in an attic.
2.) As outlined in the Figures 1, 2, and 3 the size of the combustion and ventilation air ducts depend upon where the source
of the air is located. It is important to note that all sizes are to be regarded as “free area” and any obstruction such as an
inlet or outlet grille must be made up for in the size of the openings. No screen may be used at the outlet or inlet of these
ducts which are smaller than 1/4" mesh. Any grille used must be non-moveable fixed grilles. The user should be informed
not to block or in any manner restrict these openings.
Figure 1. Shows air taken from the living area must be from two (2) permanent openings with each opening having a minimum
of 1 square inch per 1000 BTUH/ of total gas burning equipment. With a minimum of 100 square inches, one opening must
be located within 12 inches from the top of the enclosure, and the other opening is to be located within 12 inches of the bottom
of the enclosure.
Note: The openings must not originate in a bedroom, bathroom or any room which may be commonly closed.
Figure 2. Shows the combustion/ventilation air supplied to the mechanical room from the outside via horizontal ducts are
to be a minimum of 1 square inch per 2000 BTUH of total gas burning equipment.
Figure 3. Demonstrates combustion/ventilation air origination from a ventilated attic or crawl space. This type of installation
requires a minimum of 1 square inch per 4000 BTUH of total gas burning equipment contained in the enclosure. For
acceptable intake and exhaust duct location please refer to Figure 3.
3.) The combustion and ventilation air openings must be of equal size and sized appropriately.
Use the table below as a guide:
TOTAL 1000 BTUH / SQ. INCH 2000 BTUH / SQ. INCH 4000 BTUH / SQ. INCH
APPLIANCE INPUT RD. PIPE RECT. DUCT RD. PIPE RECT. DUCT RD. PIPE RECT.DUCT
60,000 11" DIA. 100 SQ. IN. 7" DIA. 30 SQ. IN. 5" DIA. 15 SQ. IN.
80,000 11" DIA. 100 SQ. IN. 8" DIA. 40 SQ. IN. 5" DIA. 20 SQ. IN.
100,000 11" DIA. 100 SQ. IN. 8" DIA. 50 SQ. IN. 6" DIA. 25 SQ. IN.
120,000 13" DIA. 120 SQ. IN. 9" DIA. 60 SQ. IN. 7" DIA. 30 SQ. IN.
The preceding table shows the combustion/ventilation air openings based upon the furnace only. If additional gas fired
equipment is installed in the mechanical room use the following work sheet to determine the combustion/ventilation air duct
size requirements:
Total Appliance Input (Furnace + all other gas fired equipment) =
BTUH per square inch requirement - 1000, 2000 or 4000 (see figures 1 through 3) =
Rectangular duct size = Total Appliance Input / BTUH per square inch requirement =
4.) When the installation is in an unconfined space in buildings of conventional frame, brick, or stone construction, normal
infiltration found in these types of construction should be adequate to provide the necessary air for combustion and ventilation.
If the unconfined space is within a building of unusually tight construction, provisions for combustion and outlet air must be
provided as shown in Figure 3.
5.) No dimension of a rectangular duct used to carry combustion or ventilation air shall be less than 3".
6.) Do not locate the combustion air source in an area which may contain corrosive chemicals such as a chlorine, sulphur,
fluorine, laundry cleaners or other damaging chemicals.
7.) If unit is installed near an exhaust fan, sufficient combustion and ventilation must be provided to prevent the exhaust fan
from creating a negative pressure in the room.
8.) Combustion Air must not be obtained from a bedroom or bathroom.
CONSULT LOCAL CODES FOR SPECIAL OR ADDITIONAL REQUIREMENTS.

VENTING
GENERAL INSTRUCTIONS:
The following instructions are intended for use by fully qualified installation or service technicians. Education of the user as
to the importance of venting inspection and annual maintenance by a qualified service technicians should be stressed by
the heating contractor at the earliest practical time.
All Venting 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.
PROPER VENT PIPE INSTALLATION IS CRITICAL TO THE SAFE OPERATION OF THE FURNACE, THEREFORE
CAREFULLY READ AND FOLLOW ALL THE INSTRUCTIONS GIVEN IN THIS SECTION. EACH VENT MUST SERVE
ONLY ONE APPLIANCE. DO NOT CONNECT TO AN EXISTING VENT OR CHIMNEY.
MATERIAL:
This furnace must be vented to the outdoors using 2 inch (3 inch required on the GMN120-5 MODEL) PVC (Polyvinyl chloride)
schedule 40 vent pipe, DWV, or equivilant. Substitutes are permitted only when approved by local codes, and are equal to
or better than PVC. Vent diameter must not be reduced or changed (except on GMN100-4 MODEL), where after 40' of 2"
PVC, any addition in length up to 60' must be 3" PVC. Elbows used to change from a vertical run to a horizontal run should
be type DWV (long radius) to provide the correct slope in horizontal run. If other types are used, then (2) 45 degree elbows
should be used in place of one 90 degree, with elbows slightly misaligned to provide slope in the horizontal runs. Materials
and procedures must conform to American Society for Testing and Materials Standard (ASTM).
Pipe and fittings - ASTM 1785, D2466 & D2665
PVC Primer and Solvent Cement - ASTM D2564
Procedure for Cementing Joints Ref ASTM D2855
INSTALLATION:
Vertical venting is preferred. ALL HORIZONTAL VENT INSTALLATIONS MUST BE IN ACCORDANCE WITH THESE
INSTRUCTIONS AND ADDITIONAL REQUIREMENTS UNDER SECTION FOR HORIZONTAL VENT.
a.) DO NOT install the vent pipe in the same chase with a vent from another gas or other fuel burning appliance.
Except with another GMN.
b.) DO NOT install vent terminal elbow on vertical vent applications.
c.) DO NOT install the vent pipe within 6 inches from another gas or fuel burning appliance.
d.) DO NOT install the condensate drain trap in any location where freezing inside the trap or drain line can occur.
e.) Drain trap must be easily accessible for checking and cleaning, and must be installed within 4 feet of the furnace.
DO NOT install trap higher than the vent blower outlet. Illustration below, shows the drain trap assembly.
10

PROTECTION FROM FREEZING
The vent pipe must be properly insulated if there is any chance of condensate freezing inside the pipe, particularly when the
pipe passes through an UNCONDITIONED SPACE or is exposed to the exterior. For exterior use, a minimum of 1 inch thick
closed cell foam insulation is recommended. For interior piping, fiber glass with a vapor barrier having “R” value of R-7 or better
may be used.
VENT LENGTH
The maximum recommended vent length is 60 total equivalent feet with each L.R. 90 degree elbow (3 max.) counted as 5
ft. and each 45 degree elbow (6 max.) counted as 2.5 ft. The vent run should be as short as possible with a minimum length
of 5 ft. for vertical run, and 3 ft. for horizontal run. When determining vent length DO NOT count vent terminal or drain trap
assembly. (S.R. elbows are equivilant to 7 1/2 ft.)
SUPPORTING AND PITCHING
All horizontal runs must be supported at least every 3 ft. with straps or hangers. No sags or dips are permitted. Maintain
1/4 inch per foot minimum pitch upward on all horizontal piping from the drain trap to the vent terminal. Horizontal pipe run
from the unit to the trap must be pitched upward a minimum of 1/4 inch per foot of run away from the drain trap assembly
so the condensate will flow into drain trap. Vertical runs must be supported every 6 ft.
JOINING PIPE AND FITTINGS
Clean pipe joint area and fitting socket of all grease, dirt and moisture. Checking pipe and socket for proper fit.
Wipe socket and pipe with cleaner-primer. Apply a generous coat of primer to connecting areas.
DO NOT ALLOW PRIMER TO DRY BEFORE APPLYING CEMENT.
Apply a thin coat of cement in the socket. Quickly apply a heavy coat of cement to the pipe end and insert pipe into fitting.
Hold the pipe in the fitting for 30 seconds.
Wipe all excess cement from the joint and allow 15 minutes before handling.
DO NOT CEMENT VENT PIPE TO VENT BLOWER OUTLET
CAUTION: For proper installation
DO NOT use solvent cement that has become curdled, lumpy or thickened.
DO NOT thin. Observe shelf precautions printed on containers.
For application below 32 degrees F use only low temperature type solvent cement.
WARNING: DANGER OF FIRE OR BODILY INJURY PVC SOLVENT CEMENTS AND PRIMERS ARE HIGHLY FLAM-
MABLE. PROVIDE ADEQUATE VENTILATION. DO NOT ASSEMBLE NEAR HEAT SOURCE OR OPEN FLAME. DO NOT
SMOKE. AVOID SKIN OR EYE CONTACT. OBSERVE ALL CAUTIONS AND WARNING PRINTED ON MATERIAL
CONTAINERS.
CONDENSATEDRAIN
This furnace is designed to remove both sensible and latent heat from the combustion flue gas. As a result, condensed water
vapor is formed in the secondary heat exchanger and drains to the drain trap outside the unit. Use 1/2 inch PVC flex tube.
Install overflow line if routing to floor drain.
DO NOT RUN CONDENSATE DRAIN TO AN OUTDOOR DRAIN
OR WHERE THE POTENTIAL FOR FREEZING CAN OCCUR.
If an indoor drain is not readily available, a condensate pump or sump pump must be used. The condensate pump must be
constructed of acid resistant materials. The condensate pump must have an auxiliary safety switch to prevent operation of
11

the furnace, resulting in overflow of condensate, in the event of pump failure.
HORIZONTAL THROUGH THE WALL VENTING INSTRUCTIONS
The furnace may be vented horizontally through an exterior wall, using all applicable instructions under “Vent Pipe
Installation” together with these additional requirements. See illustration below.
ALL HORIZONTAL VENT INSTALLATION MUST BE MADE IN ACCORDANCE WITH THESE INSTRUCTIONS.
WARNING: THE COMBUSTION PRODUCTS AND MOISTURE IN THE FLUE GAS WILL CONDENSE AND THE CONDEN-
SATE MAY FREEZE ON THE EXTERIOR WALL AND SURROUNDING SURFACES. SOME DISCOLORATION TO THE
EXTERIOR OF THE BUILDING IS TO BE EXPECTED.
When selecting the external wall which the vent is to penetrate, the following items are to be taken into consideration:
a.) When possible the vent termination is not to be exposed to the prevailing winds.
b.) The vent termination must be a minimum of 12 inches above grade level, or expected snow level.
c.) If adjacent to a public walkway, the vent termination must be a minimum of 7 feet above the walkway.
d.) Avoid area where condensate drainage may be a problem such as, flower beds, patios etc.
e.) Do not locate the termination within 4 feet of an electric meter, gas meter, or gas regulator.
f.) Do not locate the termination within 4 feet of an adjacent building.
g.) Do not locate the termination within 4 feet of an operable window.
h.) Do not locate the termination within 10 feet vertical and 3 feet horizontal from a forced air inlet.
i.) Do not locate the termination within 3 feet of an inside corner to a building.
j.) The vent gases exiting from the termination may create staining or discoloration of the exterior wall. To protect against
this action it is desirable to protect this surface for a distance of approximately 2 feet surrounding the termination with an
aluminium plate, or similar non-corrosive material.
Instruct the user to keep the area around the termination free of snow, dirt and other obstacles which could prevent normal
venting operation of the appliance
12

13
CONVERTING FURNACE TO PROPANE
WARNING: This furnace was equipped at the factory for use with NATURAL GAS. Propane conversion, if required, must
be performed by a qualified service technician experienced in performing this type of conversion. If conversion to Propane
is required, all instructions included with the factory authorized conversion kit must be followed.
GAS SUPPLY AND PIPING
Check rating plate to make certain unit is equipped to burn the type of gas supplied. Care should be taken after installation
of this equipment that gas control valve not be subjected to high gas supply line pressure.
THE FURNACE AND ITS INDIVIDUAL SHUT OFF VALVE MUST BE DISCONNECTED FROM THE GAS SUPPLY PIPING
SYSTEM DURING ANY PRESSURE TESTING OF THAT SYSTEM AT TEST PRESSURES IN EXCESS OF 1/2 PSIG
(3.48 KPA). THE FURNACE MUST BE ISOLATED FROM THE GAS SUPPLY PIPING SYSTEM BY CLOSING ITS
INDIVIDUAL MANUAL SHUT OFF VALVE DURING ANY PRESSURE TESTING OF THE GAS SUPPLY PIPING SYSTEM
AT TEST PRESSURE EQUAL TO OR LESS THAN 1/2 PSIG (3.48 KPA).
In making gas connections, avoid strains as they may cause noise and may damage controls.
IT IS IMPORTANT TO USE A BACK-UP WRENCH WHEN MAKING GAS CONNECTIONS.
IGNORING THIS PRACTICE MAY RESULT IN A FIRE HAZARD CAUSING PROPERTY DAMAGE OR DEATH.
To check for leaks in piping use a soap and water solution or other approved method. DO NOT USE AN OPEN FLAME.
CONNECT GAS SERVICE from meter to control assembly. See previous drawing for typical hook-up. A GROUND-JOINT
UNION MUSTBEINSTALLED,EXTERIOR TO THE FURNACE CABINET, SO THE CONTROL ASSEMBLY MAY BE EASILY
REMOVED. A1/8" NPT plug on the supply pipe at the valve for the purpose of making measurements of the inlet gas pressure
must also be installed. A manual shut-off valve must be installed in the gas line outside of the furnace casing. The valve
should be readily accessible for turning on or off. A capped drip leg must be installed in the gas supply line as close to the
furnace as possible. A PIPE COMPOUND RESISTANT TO THE ACTION OF LIQUEFIED PETROLEUM GASES MUST BE
USED AT ALL THREADED PIPE CONNECTIONS.
Gas piping should be installed in accordance with local codes and regulations of the utility company. Consult local gas
company for location of manual main valve. The gas line should be of adequate size to prevent undue pressure drop and
never smaller than the pipe size to the combination gas valve. It is recommended that the size of pipe selected be in
accordance with “GAS PIPE CAPACITY TABLE” for the length of pipe required and connected to the furnace as illustrated.
1/2" UNION MUST BE INSTALLED
OUTSIDE OF UNIT
1/8" NPT TAP
(GAS TEST)
TO GAS
SUPPLY
NOTE: ALL THREADS MUST BE COATED WITH A
PIPE COMPOUND RESISTANT TO THE ACTION OF
LIQUEFIED PETROLEUM GAS. MANUAL VALVE
4" ABOVE FLOOR
1/8" NPT TAP (GAS TEST)
CAPPED DRIP LEG.
CHECK LOCAL CODES FOR
LENGTH REQUIRED

14
Check both manifold pressure (using the 1/8" NPT tap located on the gas valve) and service pressure (using the 1/8" NPT
tap as shown in the drawing above).
GAS PIPE CAPACITY TABLE (CU. FT./HR)
Capacity of gas pipe of different diameters and length in cu. ft. per hr. with pressure drop of 0.3 in. and specific gravity of
0.60 (natural gas). NOTE : COPPER TUBING MUST NOT BE USED FOR NATURAL GAS INSTALLATIONS.
Nominal Iron Length of Pipe, Feet
Pipe Size, Inches 10 20 30 40 50 60 70 80
1/2 132 92 73 63 56 50 46 43
3/4 278 190 152 130 115 105 96 90
1 520 350 285 245 215 195 180 170
1 1/4 1050 730 590 500 440 400 370 350
1 1/2 1600 1100 890 760 670 610 560 530
After the length of pipe has been determined, select the pipe size which will provide the minimum cubic feet per hour required
for the gas input rating of the furnace using the formula :
Cu. Ft.Per Hr. Required = Gas Input of Furnace(BTU/HR)
Heating Value of Gas (BTU/HR)
The gas input of the furnace is marked on the furnace rating plate. The heating calorific value of the gas (BTU/Ft3) may be
determined by consulting the local natural gas utility or the L.P. gas supplier.
If your local utility/ building codes permit the use of a flexible gas line ALWAYS USE A NEW LINE. DO NOT USE FLEXIBLE
GAS LINES WHICH HAVE PREVIOUSLY SERVICED ANOTHER APPLIANCE.
CIRCULATING SUPPLY AIR AND RETURN AIR.
The circulating air return may be taken from:
(1) outside the building (2) return ducts from several rooms (3) central return (4) any combination of the above.
Note: When outside air is utilized, the system should be designed and adjusted such that the temperature of the air supply
to the furnace will not drop to below 50°F during the heating season.
When a combination of indoor and outside air is used (in conjunction with a mixing or diverting damper) the volume of air
must not be reduced.
Plenum chambers and air ducts must be installed in accordance with Standard for the Installation of Air Conditioning and
Ventilating Systems, NFPA No. 90A, or the Standard for the Installation of Warm Air Heating and Air Conditioning Systems,
NFPA No. 90B.
When the ducts are installed so that the supply ducts carry air circulated by the furnace to area outside the space containing
the furnace, the return air shall be handled by a duct or ducts sealed to the furnace casing and terminated outside the space
containing the furnace. If there is no complete return air duct system, the return air connection must be sealed to the furnace
casing and run full size to a location outside the utility room or space housing the furnace. The furnace must be installed
in a level and plumb position.
If installed in parallel with a cooling unit, the damper or other means used to control the flow of air must be adequate to prevent

15
CAUTION: ONE OF THE MOST COMMON CAUSES OF TROUBLE IN FORCED AIR HEATING SYSTEMS IS DUE TO
INSUFFICIENT RETURN AIR TO THE FURNACE. THE RETURN AIR SYSTEM SHOULD BE APPROXIMATELY EQUAL
TO OR GREATER THAN THE AREA OF THE WARM AIR DISCHARGE. CONSULT LOCAL CODES FOR SPECIAL
REQUIREMENTS. BLOWERSPEEDSHOULDBEADJUSTEDTOMAINTAINTHETEMPERATURERISERANGESHOWN
ON THE RATING PLATE.
NOTE: Upon initial start-up, some smoke or an odor may be present. This is normal and should disappear in a short amount
of time.
WARNING: IMPORTANT NOTICE - NEVER ALLOW THE PRODUCTS OF COMBUSTION OR THE FLUE PRODUCTS
TO ENTER THE RETURN DUCTWORK, OR THE CIRCULATING AIR SUPPLY. ALL RETURN DUCTWORK MUST BE
ADEQUATELY SEALED AND SECURED TO THE FURNACE AND JOINTS MUST BE COMPLETELY SEALED. ALL
OTHER DUCT JOINTS MUST BE SECURED WITH APPROVED CONNECTIONS AND SEALED AIRTIGHT. THE VENT
AND THE COMBUSTION AIR SUPPLY PIPES MUST BE PROPERLY INSTALLED TO PREVENT LEAKAGE, AS NOTED
ELSEWHERE IN THESE INSTRUCTIONS. WHEN A FURNACE IS MOUNTED ON A PLATFORM, WITH RETURN
THROUGH THE BOTTOM, IT MUST BE SEALED AIRTIGHT BETWEEN THE FURNACE AND THE RETURN AIR
PLENUM. THE FLOOR OR PLATFORM MUST PROVIDE SOUND PHYSICAL SUPPORT OF THE FURNACE WITHOUT
SAGGING, CRACKS, GAPS, ETC. AROUND THE BASE AS TO PROVIDE A SEAL BETWEEN THE SUPPORT AND
THE BASE. WHEN INSTALLED IN A CLOSET OR OTHER SIMILAR ENCLOSURE THE VENT AIR OPENINGS IN THE
CLOSET DOOR AND THE CIRCULATING AIR OPENINGS MUST BE SEPARATED AN ADEQUATE DISTANCE TO
PREVENT THE CIRCULATING AIR FROM INTERFERING WITH THE NATURAL FLOW OF VENTILATION AIR.
FAILURE TO PREVENT PRODUCTS OF COMBUSTION FROM BEING CIRCULATED INTO THE LIVING SPACE CAN
CREATE POTENTIALLY HAZARDOUS CONDITIONS, INCLUDING CARBON MONOXIDE POISONING THAT COULD
RESULT IN PERSONAL INJURY OR DEATH.
DO NOT, UNDER ANY CIRCUMSTANCES, CONNECT RETURN DUCTWORK TO ANY OTHER HEAT PRODUCING
DEVICE SUCH AS A FIREPLACE INSERT, STOVE, ETC. DOING SO MAY RESULT IN FIRE, CARBON MONOXIDE
POISONING, EXPLOSION, PERSONAL INJURY OR PROPERTY DAMAGE.
Install the air return to terminate through the floor under the furnace. For installations where return air ducts cannot be run
under the floor, return air may be taken from the side(s). When side air return is used, determine the size opening required,
and scribe a line between the knockout squares and cut out the opening along these lines.
WHERE MAXIMUM AIRFLOW IS 1800 C.F.M. OR MORE, BOTH SIDES OR THE BOTTOM MUST BE USED FOR
RETURN AIR.
WARNING: IMPORTANT NOTICE - UPFLOW FURNACES - A SOLID METAL BASE PLATE IS SUPPLIED WITH THIS
FURNACE ANDIT MUSTBE INPLACE WHENTHE FURNACE IS INSTALLED WITH SIDE AIR RETURN DUCTS. FAILURE
TO LEAVE THIS BASE PLATE IN PLACE COULD CAUSE PRODUCTS OF COMBUSTION TO BE CIRCULATED INTO
THE LIVING SPACE AND CREATE POTENTIALLY HAZARDOUS CONDITIONS, INCLUDING , BUT NOT LIMITED TO,
CARBON MONOXIDE POISONING. REFER TO SECTION ON “CIRCULATING AIR SUPPLY” FOR RETURN AIR
DUCTWORK INSTRUCTIONS.

16
ELECTRICAL CONNECTION
POWER SUPPLY
The electrical supply requirements are listed on the furnace rating plate. A separate supply line with a current overload device
and manual switch using type Twire or equivalent, with minimum rating of 63°F (35°C) temperature rise, should be run directly
from the main switch box to the junction box located inside the furnace. Copper conductors are preferred.
WARNING: Cabinet must be permanently grounded. Provisions are made for this purpose.
THE GAS SUPPLY PIPE MUST NEVER BE USED AS A GROUND OR GROUND CONNECTION.
A DEDICATED GROUND FROM THE DISCONNECT MUST BE PROVIDED.
Installation of the electric supply should be in accordance with local codes. In the absence of local codes refer to the National
Electrical Code ANSI/NFPA No. 70-1984, or latest edition, and local building codes, which can be obtained from: National
Fire Protection Association, Batterymarch, Quincy, MA 02269. In Canada: refer to the Canadian Electrical Code C22.1 Part
I the latest edition.
This equipment in polarity sensitive. The neutral (ground) connection must be connected to the equipment white power
connector. Failure to observe this practice will result in no flame sensing ability.
THERMOSTAT LOCATION AND LOW VOLTAGE CONNECTIONS
THERMOSTAT LOCATION
Install the room thermostat in accordance with the instruction sheet accompanying the thermostat. Run the thermostat lead
wires inside the control compartment. Connect the thermostat as shown on the wiring diagram. Never install a thermostat
on an outside wall or where it will be influenced by drafts, concealed hot or cold water pipes, ducts, lighting fixtures, radiation
from a fireplace, rays of the sun, lamps, televisions, radios or air streams from warm air registers.
LOW VOLTAGE ELECTRICAL CONNECTIONS
To facilitate the thermostat connections to the appliance, low voltage wiring extends through the furnace cabinet and is
wrapped with a label titled "Thermostat Wiring". Connect the field supplied low voltage wiring to the appliance wiring using
solderless connectors. Color coding should be adhered to in order to facilitate future troubleshooting.
YG
WR
YELLOW
ROOMTHERMOSTAT
BLUE
GREEN
RED
WHITE
CONDENSER

17
SETTING THE THERMOSTAT HEAT ANTICIPATOR
The method shown below should be used in measuring the amp draw of the low voltage circuit to assure proper adjustment
of the thermostat heat anticipator.
WRAP THE THERMOSTAT WIRE 10 TIMES AROUND
THE METER LEG AND DIVIDE THE RESULT BY 10
EXAMPLE:
IF METER READS 4 AMPS
SET THE HEAT ANTICIPATOR
AT .4 (4/10 = .4).
"W" FROM ROOM
THERMOSTAT
CLAMP ON AMP METER
TO RATE FURNACE
GENERAL
The meter time and orifice sizes indicated in these instructions are for equipment to be installed using Natural Gas. If Propane
Gas is used refer to instructions supplied with the conversion kit. High Altitude application requires the conversion kit HAO2.
It is important to check the furnace input to prevent over firing beyond the design-rated input. NEVER SET INPUT ABOVE
THAT SHOWN ON THE RATING PLATE. Furnace firing rate is controlled by inlet pressure, manifold pressure, burner orifices,
heating value of the gas. This furnace is equipped with the correct burner orifices for installations between 0 to 2000 feet and
normally do not have to be changed. Applications over 2000 feet require factory equipped orifices to be replaced by burner
orifices selected from the table below resulting in the furnace input being reduced at a rate of 4% for each 1000 feet above
sea-level (U.S. only).
ALTITUDE BURNER ORIFICE
NATURAL GAS
0-2000 45
3000 47
4000 47
5000 47
6000 48
7000 48
For altitudes above 7000 feet refer to appropriate section of the National Fuel Gas Code, ANSI Z223.1. If re-orificing is required
this must be performed prior to timing the gas meter. THE GAS AND ELECTRIC SUPPLY MUST BE OFF BEFORE
INSTALLING NEW BURNER ORIFICES. To calculate the furnace input of a furnace installed over 2000 feet you must use
the following formula and not the table supplied.
CORRECTED INPUT (BTUH) = NAMEPLATE INPUT - (ALTITUDE x .04) x (NAMEPLATE INPUT / 1000)
Input BTU/HR = Heating Value of Gas (BTU/FT3) x 3600
Time in Second (for 1 cu.ft.) of Gas
HIGH ALTITUDE CONVERSIONS FOR CANADIAN INSTALLATIONS :
In Canada the name plate input rating for the furnaces apply if\or installations up to 2,000 feet (610 m) above sea level. Kit
No. HA02 for Natural Gas and for Propane Gas is required to convert the furnaces to elevations from 2,000 to 4,500 feet (610
to 1,370 m) above sea level. Canadian Certification applies to the Installations of furnaces up to 4,500 feet (1,370 m) above
sea level. Installations above 4,500 feet (1,370 m) above sea level is subject to acceptance by the local authorities having
jurisdiction.

18
chilled air from entering the furnace, and if manually operated must be equipped with means to prevent operation of the other
unit unless the damper is in the full heat or cool position.
EXAMPLE :
Corrected input for a GMN100-4 installed at an elevation of 6,000 feet using Natural Gas with
a heating value of 1000 (BTUH) is =
Corrected Input (BTUH) = 100,000 - (6,000 x .04) x (100,000/ 1,000)
Corrected Input (BTUH) = 100,000 -(240 x 100)
Corrected Input (BTUH) = 100,000 - 24,000
Corrected Input (BTUH) = 76,000
Using the orifices shown in the table for 6000 feet elevation (#48). A meter time of 48.0 seconds is measured.
The actual firing rate of the furnace =
Input BTUH = 1,000 (Heating Value of Gas) x 3,600
48.0 Meter time for 1 cubic foot of gas)
Input BTUH = 3,600,000 / 48.0
Input BTUH = 75,000 BTUH
TIMING THE GAS METER
Use the following method to time determine the firing rate of the furnace. Location of inlet and manifold pressure taps are
shown in the “GAS SUPPLY AND PIPING” section of these instructions.
Before attempting any service or adjustments - Insure that Gas & Electrical Supplies are "OFF".
1.) Install a manometer graduated in tenths of an inch of water column on the inlet pressure tap.
2.) Remove plug at the “Manifold Pressure Tap” on the gas valve and install second manometer.
3.) Determine the size of the gas meter being used.
4.) Shut off all other gas appliances with the exception of pilot burners.
5.) Place the furnace into operation.
6.) Adjust inlet pressure to obtain a pressure range between 5" and 7" W.C.
7.) After 15 minutes of furnace operation, time meter with an accurate stop watch for 2 revolutions.
8.) Divide time obtained in step 7 by 2.
9.) Use the appropriate table or formula to determine firing input.
10.) If necessary, adjust manifold pressure at the gas valve by removing the regulator cap and turn adjustment screw
clockwise to obtain a higher pressure or counterclockwise to reduce manifold pressure. Manifold pressure must be within
a range of 3.2" to 3.8" W.C. Inability to obtain the correct firing rate will result in the need to re-orifice. If manifold pressure
or re-orificing is necessary repeat steps 4 through 10 after the furnace has been allowed to cool down for approximately 10
- 15 minutes.
11.) Turn off gas and electric supply, remove manometers and replace any plug removed in steps 1 and 2, using a joint
compound resistant to L.P. Gas.
METER TIME IN MINUTES AND SECOND FOR NORMAL INPUT RATING
OF FURNACES EQUIPPED FOR NATURAL GAS. 0-2000 FEET ALTITUDE
Nameplate Meter Heating Value of Gas BTU per Cu.Ft.
Input Size 900 1000 1040 1100
BTU/Hr. Cu.Ft. Min. Sec. Min. Sec. Min. Sec. Min. Sec.
60,000 1 0 54 1 00 1 03 1 06
10 9 00100010241100
80,000 1 0 41 0 45 0 47 0 50
10 6 45 7 30 7 48 8 15
100,000 1 0 32 0 36 0 37 0 40
10 5 24 6 00 6 14 6 36
120,000 1 0 27 0 30 0 31 0 33
10 4 30 5 00 5 12 5 30
Input BTU/HR = Heating Value of Gas (BTU/FT3) x 3600
Time in Second (for 1 cu.ft.) of Gas

19
MAIN BURNER ADJUSTMENT
MAIN BURNER
After furnace has been in operation for approximately five minutes, close the air shutters until yellow tips appear on the flames.
Now open the air shutter until yellow tips just disappear and the flames have soft blue cones. Repeat this procedure on all
burners. Lock the air shutters by means of the lock screw.
SAFETY CONTROLS FUNCTIONS AND CHECKOUT PROCEDURE
GENERAL
In most cases all safety switches used on this furnace are wired in series through the furnace “W” leg. It is important never
to bypass, alter or tamper with any safety control on this furnace. Safety features of this furnace must be checked at time
of installation to assure proper operation of the furnace.
MAIN LIMIT SWITCH
High limit switch used is a 1/2" dia. disk switch, designed to shut off the gas to the burners if the outlet air exceeds the max.
design outlet temperature. High limit cut-off is non-adjustable. To check the control operation, block the air flow through the
unit temporarily. The limit switch should function to turn off the automatic gas valve within a few minutes. Remove blockage
immediately after switch operates.
VENT PRESSURE SWITCH
This furnace uses a vent pressure switch to prevent the furnace from operating if the vent blower should fail to operate or a
restriction in the venting system occurs. DO NOT tamper with or bypass this switch. For more details of the venting
installation see the section titled “VENTING”. To check this switch remove the hose from the vent motor with the burners
ignited. The switch should function and turn off the burners immediately. Reinstall the rubber hose and the burners should
ignite.
FLAME ROLL-OUT SWITCH
This furnace is equipped with (2) flame roll-out switches. These 1/2" dia., manual reset switches are located in the burner
vestibule. These switches are designed to shut down the burners in event presence of flame is detected outside the heat
exchanger. To reset the switch you must depress the button on the top of the switch. With the furnace in operation place
an open flame (candle, match, cigarette lighter etc.) under this switch with the flame touching the sensing element. The
switch should function in a short time and the burners should extinguish. Reset the switch.
FLAME SENSOR
Main burner ignition is provided by a Hot Surface ignition system. The main burners should extinguish if the flame sensor
fails to detect burner flame. Disconnect the sensor lead to the module. Place the furnace into operation. The ignitor should
glow, the burners ignite; however the burners should shut off after a few seconds of operation. Reconnect the sensor lead
and follow the lighting instructions to restore the furnace to its operational condition.
BLOWER DOOR INTERLOCK SWITCH
AIR SHUTTER
AIR SHUTTER
LOCKING SCREW
BURNER OUTER MANTLE
BURNER INNER MANTLE

20
The purpose of this device is to disconnect all power to the furnace in event the blower door should become dislodged or
is not installed. Operation of this furnace with the blower door being out of position will allow toxic combustion fumes to be
transmitted into the living area via the circulating air blower. With the furnace in operation remove the blower door, the blower
and burners should stop. Replace blower door.
STACK OVERTEMP SWITCH
Mounted on the Vent blower housing, this switch is designed to shut down the burners if the main blower should fail to operate.
To test this switch disconnect the main blower, bypass the main limit, and place the furnace into operation. After a period
of time this switch should function and the burners extinguish. IT IS IMPORTANT TO REMOVE THE JUMPER FROM THE
MAIN LIMIT AND RECONNECT THE BLOWER prior to returning this furnace into operation.
FAN CONTROL / IGNITION MODULE
This appliance is equipped with an integrated hot surface ignition module / fan control. The function of this device is to ignite
the burners and to control the blower and venter functions.
When a call for heat is generated by the room thermostat the control activates the vent blower relay. After a short pre-purge
the hot surface ignitor is energized. The main valve is opened after the ignitor has been glowing for about 17 seconds. If
main burner flame is detected by the flame sensor (see flame sensor section) the burners will continue operation.
Unlike the traditional thermal fan control this device activates the blower at a predetermined time (nominal 30 seconds) after
the main valve is energized, not after the bonnet has achieved a certain temperature. This control is located in the blower
compartment. The blower motor is deactivated approximately 2 1/2 minutes after the burners are extinguished.
CIRCULATING AIR FILTERS
CAUTION: DISCONNECT THE MAIN POWER TO THE UNIT BEFORE ATTEMPTING ANY MAINTENANCE.
1.) Keep the air filters clean.
2.) Inspect filters monthly and replace when necessary. A new home may require more frequent attention
to the filters until dust from construction is removed.
3.) Permanent filters may be cleaned by using a vacuum cleaner and washing with detergent and water.
Air dry thoroughly and reinstall. Disposable filters cannot be cleaned.
CAUTION : DO NOT OPERATE YOUR SYSTEM FOR EXTENDED PERIODS WITHOUT FILTERS. DUST IN
THE AIR WILL RESTRICT THE AIR MOVEMENT OVER THE SECONDARY (CONDENSING) COIL
CAUSING NUISANCE CYCLING OF SAFETY CONTROL AND CAUSE A "NO HEAT" CONDITION.
MINIMUM FILTER SIZES
Furnace Width Filter Size Type
14" 14 x 25 x 1 Perm.
17-1/2" 16 x 25 x 1 Perm.
21" 20 x 25 x 1 Perm.
24-1/2" 24 x 25 x 1 Perm.