Unitary products group GY8S*DH, GM8S*DH, LM8S*DH, LY8S*DH Installation Manual

INSTALLATION MANUAL

HIGH EFFICIENCY
TUBULAR HEAT EXCHANGER SERIES

MODELS: GY8S*DH / GM8S*DH / LY8S*DH / LM8S*DH
(Single Stage Downflow / Horizontal / Low NOx)

40 - 130 MBH INPUT
(11.72 - 38.10 KW) INPUT

LIST OF SECTIONS

SAFETY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

DUCTWORK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

FILTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

GAS PIPING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

ELECTRICAL POWER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

LIST OF FIGURES

Combustible Floor Base Accessory . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Typical Attic Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Typical Suspended Furnace / Crawl Space Installation . . . . . . . . . . . .7

Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Gas Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Downflow Gas Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Horizontal Gas Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Electrical Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Thermostat Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

Accessory Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Typical Twinned Furnace Application . . . . . . . . . . . . . . . . . . . . . . . . 12

Single Stage Twinning Wiring Diagram . . . . . . . . . . . . . . . . . . . . . . . 13

Two-Stage Twinning Wiring Diagram . . . . . . . . . . . . . . . . . . . . . . . . . 13

Vent Termination 10 ft. (3.0 m) or less . . . . . . . . . . . . . . . . . . . . . . . .14

Vent Termination more than 10 ft. (3.0 m) . . . . . . . . . . . . . . . . . . . . .14

TWINNING AND STAGING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

VENT SYSTEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

SAFETY CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

START-UP AND ADJUSTMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . .20

WIRING DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

Vent Termination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Typical Sidewall Vent Application . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

Typical Sidewall Vent and Termination Configuration . . . . . . . . . . . .15

Home Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

Combustion Airflow Path Through The Furnace Casing . . . . . . . . . .17

Alternate Air Intake, Air Outlet and Chimney Connections . . . . . . . . .17

Air Inlet, Outlet and Chimney Connections . . . . . . . . . . . . . . . . . . . . .17

Typical Chimney Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Horizontal Air Inlet, Outlet and Chimney Connections . . . . . . . . . . . .18

Outside and Ambient Combustion Air . . . . . . . . . . . . . . . . . . . . . . . . .18

Pressure Switch Tubing Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

Gas Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

Reading Gas Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

Furnace Control Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Wiring Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

EFFICIENCY
RATING
CERTIFIED

ISO 9001

Certified Quality

Management System

LIST OF TABLES

Unit Clearances to Combustibles . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Minimum Duct Sizing For Proper Airflow . . . . . . . . . . . . . . . . . . . . . . . 5

Round Duct Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Cabinet and Duct Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Recommended Filter Sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Nominal Manifold Pressure - High Fire . . . . . . . . . . . . . . . . . . . . . . . .9

Ratings & Physical / Electrical Data . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Roof Pitch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

SECTION I: SAFETY

This is a safety alert symbol. When you see this symbol on
labels or in manuals, be alert to the potential for personal
injury.

Understand and pay particular attention to the signal words DANGER,

WARNING, or CAUTION.
DANGER indicates an imminently hazardous situation, which, if not

avoided, will result in death or serious injury
WARNING indicates a potentially hazardous situation, which, if not

avoided, could result in death or serious injury
CAUTION indicates a potentially hazardous situation, which, if not

avoided may result in minor or mo derate injury.
alert against unsafe practices and hazards involving only property dam­age.

.

.

It is also used to

Estimated Free Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Unconfined Space Minimum Area in Square Inch . . . . . . . . . . . . . . .18

Free Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

Inlet Gas Pressure Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

Nominal Manifold Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

Filter Performance - Pressure Drop Inches W.C. and (kPa) . . . . . . . .24

Blower Performance CFM - (without filter) . . . . . . . . . . . . . . . . . . . . .25

Field Installed Accessories - Non Electrical . . . . . . . . . . . . . . . . . . . .26

Improper installation may create a condition where the operation of
the product could cause personal injury or property damage.

Improper installation, adjustment, alteration, service or mainte­nance can cause injury or property damage. Refer to this manual
for assistance or for additional information, consult a qualified con­tractor, installer or service agency.

This product must be installed in strict compliance with the installa­tion instructions and any applicable local, state, and national codes
including, but not limited to building, electrical, and mechanical
codes.

268894-UIM-A-0407

268894-UIM-A-0407

SPECIFIC SAFETY RULES AND PRECAUTIONS

1. Only Natural gas or Propane (LP) gas are approved for use with
this furnace. Refer to the furnace rating plate or SECTION IV of
these instructions.

2. Install this furnace only in a location and position as specified in
SECTION I of these instructions.

3. A gas-fired furnace for installation in a residential garage must be
installed as specified in SECTION I of these instructions.

4. Provide adequate combustion and ventilation air to the furnace
space as specified in SECTION VI of these instructions.

5. Combustion products must be discharged outdoors. Connect this
furnace to an approved vent system only, as specified in SEC­TION VI of these instructions.

FIRE OR EXPLOSION HAZARD
Failure to follow the safety warnings exactly could result in serious
injury, death or property damage.
Never test for gas leaks with an open flame. Use a commercially
available soap solution made specifically for detection of leaks to
check all connections. A fire or explosion may result causing prop­erty damage, personal injury or loss of life.

6. Test for gas leaks as specified in SECTION VIII of these instruc­tions.

7. Always install the furnace to operate within the furnace’s intended
temperature rise range. Only connect the furnace to a duct system
which has an external static pressure within the allowable range,
as specified on the furnace rating plate.

8. When a furnace is installed so that supply ducts carry air circulated
by the furnace to areas outside the space containing the furnace,
the return air shall also be handled by duct(s) sealed to the fur­nace casing and terminating outside the space containing the fur­nace.

9. It is permitted to use the furnace for heating of buildings or struc­tures under construction. Installation must comply with all manu­facturer’s installation instructions including:

• Proper vent installation;

• Furnace operating under thermostatic control;

• Return air duct sealed to the furnace;

• Air filters in place;

• Set furnace input rate and temperature rise per rating plate

marking;

• Means for providing outdoor air required for combustion;

• Return air temperature maintained between 55ºF (13ºC) and

80ºF (27ºC);

• The air filter must be replaced upon substantial completion of

the construction process;

• Clean furnace, duct work and components upon substantial

completion of the construction process, and verify furnace­operating conditions including ignition, input rate, temperature
rise and venting, according to the manufacturer’s instructions.

10. When installed in an Approved Modular Home or building con­structed on-site, combustion air shall not be supplied from occu­pied spaces.

11. The size of the unit should be based on an acceptable heat loss
calculation for the structure. ACCA, Manual J or other approved
methods may be used.

SAFETY REQUIREMENTS

• This furnace should be installed in accordance with all national
and local building/safety codes and requirements, local plumbing
or waste water codes, and other applicable codes. In the absence
of local codes, install in accordance with the National Fuel Gas
Code ANSI Z223.1/NFPA 54, National Fuel Gas Code, and/or
CAN/CGA B149.1 Natural Gas and Propane Installation Code
(latest editions). Furnaces have been certified to the latest edition
of standard ANSI Z21-47 • CSA 2.3.

• Refer to the unit rating plate for the furnace model number, and
then see the dimensions page of this instruction for return air ple­num dimensions in Figure 4. The plenum must be installed
according to the instructions.

• Provide clearances from combustible materials as listed under
Clearances to Combustibles in Table 1.

• Provide clearances for servicing ensuring that service access is
allowed for both the burners and blower.

• These models ARE NOT
into a Manufactured (Mobile) Home

• This furnace is not approved for installation in trailers or recre­ational vehicles.

• Failure to carefully read and follow all instructions in this
manual can result in furnace malfunction, death, personal
injury and/or property damage.

• Furnaces for installation on combustible flooring shall not be
installed directly on carpeting, tile or other combustible material
other than wood flooring.

• Check the rating plate and power supply to be sure that the elec­trical characteristics match. All models use nominal 115 VAC, 1
Phase, 60-Hertz power supply. DO NOT CONNECT THIS APPLI­ANCE TO A 50 HZ POWER SUPPLY OR A VOLTAGE ABOVE
130 VOLTS.

• Furnace shall be installed so the electrical components are pro­tected from water.

• Installing and servicing heating equipment can be hazardous due
to the electrical components and the gas fired components. Only
trained and qualified personnel should install, repair, or service
gas heating equipment. Untrained service personnel can perform
basic maintenance functions such as cleaning and replacing the
air filters. When working on heating equipment, observe precau­tions in the manuals and on the labels attached to the unit and
other safety precautions that may apply.

• These instructions cover minimum requirements and conform to
existing national standards and safety codes. In some instances
these instructions exceed certain local codes and ordinances,
especially those who have not kept up with changing residential
and modular home construction practices. These instructions are
required as a minimum for a safe installation.

CSA listed or approved for installation

.

COMBUSTION AIR QUALITY
(LIST OF CONTAMINANTS)

The furnace will require OUTDOOR AIR for combustion when the fur­nace is located in any of the following environments.

• Restricted Environments

• Commercial buildings

• Buildings with indoor pools

• Furnaces installed in laundry rooms

• Furnaces installed in hobby or craft rooms

• Furnaces installed near chemical storage areas

• Chemical exposure

The furnace will require OUTDOOR AIR for combustion when the fur­nace is located in an area where the furnace is being exposed to the fol­lowing substances and / or chemicals.

• Permanent wave solutions

• Chlorinated waxes and cleaners

• Chlorine based swimming pool chemicals

• Water softening chemicals

• De-icing salts or chemicals

• Carbon tetrachloride

• Halogen type refrigerants

• Cleaning solvents (such as perchloroethylene)

• Printing inks, paint removers, varnishes, etc.

• Hydrochloric acid

• Cements and glues

• Anti-static fabric softeners for clothes dryers

• Masonry acid washing materials

When outdoor air is used for combustion, the combustion air intake duct
system termination must be located external to the building and in an
area where there will be no exposure to the substances listed above.

2 Unitary Products Group

The furnace area must not be used as a broom closet or for any
other storage purposes, as a fire hazard may be created. Never
store items such as the following on, near, or in contact with the fur­nace.

1. Spray or aerosol cans, rags, brooms, dust mops, vacuum
cleaners or other cleaning tools.

2. Soap powders, bleaches, waxes or other cleaning com­pounds; plastic items or containers; gasoline, kerosene, ciga­rette lighter fluid, dry cleaning fluids or other volatile fluid.

3. Paint thinners and other painting compounds.

4. Paper bags, boxes or other paper products

Never operate the furnace with the blower door removed. To
do so could result in serious personal injury and/or equipment
damage.

FOR FURNACES INSTALLED IN THE COMMON­WEALTH OF MASSACHUSETTS ONLY

For all side wall horizontally vented gas fueled equipment installed in
every dwelling, building or structure used in whole or in part for resi­dential purposes, including those owned or operated by the Com­monwealth and where the side wall exhaust vent termination is less
than seven (7) feet above finished grade in the area of the venting,
including but not limited to decks and porches, the following require­ments shall be satisfied:

1. INSTALLATION OF CARBON MONOXIDE DETECTORS. At
the time of installation of the side wall horizontal vented gas
fueled equipment, the installing plumber or gasfitter shall
observe that a hard wired carbon monoxide detector with an
alarm and battery back-up is installed on the floor level where
the gas equipment is to be installed. In addition, the installing
plumber or gasfitter shall observe that a battery operated or
hard wired carbon monoxide detector with an alarm is installed
on each additional level of the dwelling, building or structure
served by the side wall horizontal vented gas fueled equipment.
It shall be the responsibility of the property owner to secure the
services of qualified licensed professionals for the installation of
hard wired carbon monoxide detectors

a. In the event that the side wall horizontally vented gas

fueled equipment is installed in a crawl space or an attic,
the hard wired carbon monoxide detector with alarm and
battery back-up may be installed on the next adjacent floor
level.

b. In the event that the requirements of this subdivision can

not be met at the time of completion of installation, the
owner shall have a period of thirty (30) days to comply with
the above requirements; provided, however, that during
said thirty (30) day period, a battery operated carbon mon­oxide detector with an alarm shall be installed.

2. APPROVED CARBON MONOXIDE DETECTORS. Each car­bon monoxide detector as required in accordance with the
above provisions shall comply with NFPA 720 and be ANSI/UL
2034 listed and IAS certified.

3. SIGNAGE. A metal or plastic identification plate shall be perma­nently mounted to the exterior of the building at a minimum
height of eight (8) feet above grade directly in line with the
exhaust vent terminal for the horizontally vented gas fueled
heating appliance or equipment. The sign shall read, in print
size no less than one-half (1/2) inch in size, "GAS VENT

DIRECTLY BELOW. KEEP CLEAR OF ALL OBSTRUC­TIONS".

4. INSPECTION. The state or local gas inspector of the side wall
horizontally vented gas fueled equipment shall not approve the
installation unless, upon inspection, the inspector observes car­bon monoxide detectors and signage installed in accordance
with the provisions of 248 CMR 5.08(2)(a)1 through 4.

268894-UIM-A-0407

INSPECTION

As soon as a unit is received, it should be inspected for possib le dam­age during transit. If damage is evident, the extent of the damage
should be noted on the carrier’s freight bill. A separate request for
inspection by the carrier’s agent should be made in writing. Also, before
installation the unit should be checked for screws or bolts, which may
have loosened in transit. There are no shipping or spacer brackets
which need to be removed.

FURNACE LOCATION AND CLEARANCES

The furnace shall be located using the following guidelines:

1. Where a minimum amount of air intake/vent piping and elbows will
be required.

2. As centralized with the air distribution as possible.

3. Where adequate combustion air will be available (particularly
when the appliance is not using outdoor combustion air).

4. Where it will not interfere with proper air circulation in the confined
space.

5. Where the outdoor vent terminal will not be blocked or restricted.
Refer to “VENT CLEARANCES” located in SECTION VI of these
instructions. These minimum clearances must be maintained in
the installation.

6. Where the unit will be installed in a level position with no more
than 1/4” (0.64 cm) slope side-to-side and front-to-back.

Installation in freezing temperatures:

1. Furnace shall be installed in an area where ventilation facilities
provide for safe limits of ambient temperature under normal oper­ating conditions. Ambient temperatures may fall below 32° F (0° C)
providing the flue temperature does not fall below 260° F (127° C)
at any point in the flue pipe between the furnace and the chimney
or a B-Vent. The flue products will condense in the vent pipe if the
flue temperature falls below 260° F (127° C) causing the vent pipe
to deteriorate rapidly.

2. Do not allow return air temperature to be below 55º F (13° C) for
extended periods. To do so may cause condensation to occur in
the main heat exchanger, leading to premature heat exchanger
failure.

Improper installation in an ambient below 32ºF (0.0° C) could create
a hazard, resulting in damage, injury or death.

3. If this furnace is installed in an unconditioned space and an
extended power failure occurs, there will be potential damage to
the internal components. Following a power failure situation, do
not operate the unit until inspection and repairs are performed.

Clearances for access:

Ample clearances should be provided to permit easy access to the unit.
The following minimum clearances are recommended:

1. Twenty-four (24) inches (61 cm) between the front of the furnace
and an adjacent wall or another appliance, when access is
required for servicing and cleaning.

2. Eighteen (18) inches (46 cm) at the side where access is required
for passage to the front when servicing or for inspection or
replacement of flue/vent connections.

In all cases, accessibility clearances shall take precedence over clear­ances for combustible materials where accessibility clearances are
greater.

Unitary Products Group 3

268894-UIM-A-0407

Downflow furnaces for installation on combustible flooring only
when installed on the accessory combustible floor base on wood
flooring only and shall not be installed directly on carpeting, tile or
other combustible material.

Check the rating plate and power supply to be sure that the electri­cal characteristics match. All models use nominal 115 VAC, 1
Phase 60Hz power supply.

Furnace shall be installed so the electrical components are pro­tected from water.

Installation in a residential garage:

A gas-fired furnace for installation in a residential garage must be
installed so the burner(s) and the ignition source are located not less
than eighteen (18) inches (46 cm) above the floor, and the furnace must
be located or protected to avoid physical damage by vehicles.

TABLE 1:

Unit Clearances to Combustibles

Application

Top Front Rear Left Side Right Side Flue

In. (cm) In. (cm) In. (cm) In. (cm) In. (cm) In. (cm)

Downflow 1 (2.5) 6 (15.2) 0 (0.0) 0 (0.0) 3 (7.6) 6 (15.2)

Downflow B-Vent 1 (2.5) 3 (7.6) 0 (0.0) 0 (0.0) 0 (0.0) 1 (2.5)

Floor/

Bottom

1 (25.4)
1 (25.4)

Closet Alcove Attic

1

Yes Yes Yes No

1

Yes Yes Yes No

Horizontal 1 (2.5) 6 (15.2) 0 (0.0) 0 (0.0) 3 (7.6) 6 (15.2) Combustible No Yes Yes

Horizontal B-Vent 1 (2.5) 3 (7.6) 0 (0.0) 0 (0.0) 0 (0.0) 1 (2.5) Combustible No Yes Yes

1. Special floor base or air conditioning coil required for use on combustible floor.

2. Line contact only permitted between lines formed by the intersection of the rear panel and side panel (top in horizontal position) of the furnace jacket and building joists, studs or framing.

SECTION II: DUCTWORK

DUCTWORK GENERAL INFORMATION

The duct system’s design and installation must:

1. Handle an air volume appropriate for the served space and within
the operating parameters of the furnace specifications.

2. Be installed in accordance with standards of NFPA (National Fire
Protection Association) as outlined in NFPA pamphlets 90A and
90B (latest editions) or applicable national, provincial, or state, and
local fire and safety codes.

3. Create a closed duct system. For residential and Modular Home
installations, when a furnace is installed so that the supply ducts
carry air circulated by the furnace to areas outside the space con­taining the furnace, the return air shall also be handled by a
duct(s) sealed to the furnace casing and terminating outside the
space containing the furnace.

4. Complete a path for heated or cooled air to circulate through the
air conditioning and heating equipment and to and from the condi­tioned space.

The cooling coil must be installed in the supply air duct, down­stream of the furnace. Cooled air may not be passed over the heat
exchanger.

When the furnace is used in conjunction with a cooling coil, the coil
must be installed parallel with, or in the supply air side of the furnace to
avoid condensation in the primary heat exchanger. When a parallel flow
arrangement is used, dampers or other means used to control airflow
must be adequate to prevent chilled air from entering the furnace. If
manually operated, the damper must be equipped with means to pre­vent the furnace or the air conditioner from operating unless the damper
is in full heat or cool position.

The duct system must be properly sized to obtain the correct airflow
for the furnace size that is being installed.

Refer to Table 7 and the furnace rating plate for the correct rise
range and static pressures

If the ducts are undersized, the result will be high duct static pres­sures and/or high temperature rises which can result in a heat
exchanger OVERHEATING CONDITION. This condition can result
in premature heat exchanger failure, which can result in personal
injury, property damage, or death.

FLOOR BASE AND DUCTWORK INSTALLATION

Downflow Combustible Floor Base

Installations on combustible material or floors must use a
combustible floor base shown in Figure 1. Follow the
instructions supplied with the combustible floor base acces­sory. This combustible floor base can be replaced with a
matching cooling coil, properly sealed to prevent leaks. Fol­low the instructions supplied with the cooling coil cabinet for
installing the cabinet to the duct connector. Refer to the
installation instructions for additional information.

Downflow Duct Connectors

All downflow installations must use a suitable duct connector approved
by the furnace manufacturer for use with this furnace. The duct connec­tors are designed to be connected to the rectangular duct under the
floor and sealed. Refer to the instructions supplied with the duct con­nector for proper installation. Refer to the separate accessory parts list
at the end of these instructions for the approved accessory duct con­nectors.

When replacing an existing furnace, if the existing plenum is not the
same size as the new furnace then the existing plenum must be
removed and a new plenum installed that is the proper size for the new
furnace.

The duct system is a very important part of the installation. If the duct

system is improperly sized the furnace will not operate properly.

The ducts attached to the furnace plenum, should be of sufficient size
so that the furnace operates at the specified external static pressure
and within the air temperature rise specified on the nameplate.

Line

Contact

2

Yes

2

Yes

4 Unitary Products Group

268894-UIM-A-0407

Table 2 is a guide for determining whether the rectangular duct system
that the furnace is being connected to be of sufficient size for proper fur­nace operation.

Use the Example below to help you in calculating the duct area to deter­mine whether the ducts have sufficient area so that the furnace oper­ates at the specified external static pressure and within the air
temperature rise specified on the nameplate.

The following are general duct sizing guidelines that may not serve to
requirements of every application.

Example: The furnace input is 80,000 BTUH with 1,200 CFM blower
requirement. The recommended duct area is 216 sq. in, there are two 8
x 12 rectangular ducts attached to the plenum and there are two 7 inch

1. Take 8 x 12, which equals 96 sq. in. X 2, which equals 192 square
inches then go to round duct size located in Table 3.

2. The square inch area for 7 inch round ducts is 38.4 sq. in. x 2 =

76.8 square inches.

3. Then take the 192 square inch from the rectangular duct and add it
to the 76.8 sq. in. of round duct. The total square inch of duct
attached to the furnace supply plenum is 268.8 total square
inches. This exceeds the recommended 216 square inch of duct.

In this example, the duct system attached to the plenum has a sufficient
area so that the furnace operates at the specified external static pres­sure and within the air temperature rise specified on the nameplate,
providing the return duct is properly sized as well.

round ducts attached to the furnace.

TABLE 2:

Input/Cabinet Airflow

Minimum Duct Sizing For Proper Airflow

1

Return

Rectangular

2

Round

2

Supply

3

Rectangular

2

Round

BTU/H (kW) CFM (m³) In² (cm²) in. x in. (cm x cm) in. (cm) dia. In² (cm²) in. x in. (cm x cm) in. (cm) dia.

40/A (11.7) 1200 (34.0) 280 (1806) 14 x 20 (35.6 x 50.8) 18 (45.7) 216 (1394) 12 x 18 (30.5 x 45.7) 16 (40.6)
60/A (17.6) 1200 (34.0) 280 (1806) 14 x 20 (35.6 x 50.8) 18 (45.7) 216 (1394) 12 x 18 (30.5 x 45.7) 16 (40.6)
80/A (23.4) 1200 (34.0) 280 (1806) 14 x 20 (35.6 x 50.8) 18 (45.7) 216 (1394) 12 x 18 (30.5 x 45.7) 16 (40.6)
80/B (23.4) 1600 (45.3) 360 (2322) 18 x 20 (45.7 x 50.8) 22 (55.8) 280 (1806) 14 x 20 (35.6 x 50.8) 18 (45.7)

80/C (23.4) 1600 (45.3) 360 (2322) 18 x 20 (45.7 x 50.8) 22 (55.8) 280 (1806) 14 x 20 (35.6 x 50.8) 18 (45.7)

100/B (29.3) 1200 (34.0) 280 (1806) 14 x 20 (35.6 x 50.8) 18 (45.7) 216 (1394) 12 x 18 (30.5 x 45.7) 16 (40.6)
100/C (29.3) 1600 (45.3) 360 (2322) 18 x 20 (45.7 x 50.8) 22 (55.8) 280 (1806) 14 x 20 (35.6 x 50.8) 18 (45.7)
100/C (29.3) 2000 (56.6) 440 (2834) 20 x 22 (50.8 x 55.8) 24 (60.9) 390 (2516) 16 x 22 (40.6 x 55.8) 22 (55.8)
115/C (33.7) 1600 (45.3) 360 (2322) 18 x 20 (45.7 x 50.8) 22 (55.8) 280 (1806) 14 x 20 (35.6 x 50.8) 18 (45.7)
115/C (33.7) 2000 (56.6) 440 (2834) 20 x 22 (50.8 x 55.8) 24 (60.9) 390 (2516) 16 x 22 (40.6 x 55.8) 22 (55.8)
130/D (38.1) 2000 (56.6) 440 (2834) 20 x 22 (50.8 x 55.8) 24 (60.9) 390 (2516) 16 x 22 (40.6 x 55.8) 22 (55.8)

NOTE: This chart does not replace proper duct sizing calculations or take into account static pressure drop for run length and fittings. Watch out for the temperature rise and static pressures.

1. Maximum return air velocity in rigid duct @ 700 feet per minute (213 m/min).

2. Example return main trunk duct minimum dimensions.

3. Maximum supply air velocity in rigid duct @ 900 feet per minute (274 m/min).

TABLE 3:

Round Duct Size

Round Duct Size Calculated Area For Each Round Duct Size

inches (cm)

Sq.in (cm

2

)

5 (13) 19.6 (126)
6 (15) 28.2 (182)
7 (18) 38.4 (248)
8 (20) 50.2 (324)

Home duct designs.
IMPORTANT: If the supply air duct is being connected to the furnace

without the use of an accessory duct connector, then a transition duct
must be installed with flanges or tabs that are securely attached and
sealed to the supply air duct and to the base of the furnace. The transi­tion duct must have insulation between the transition duct and any com­bustible material.

The transition duct must be the same dimensional size as the rectangu­lar opening in the base of the furnace.

9 (23) 63.6 (410)
10 (25) 78.5 (506)
11 (28) 95 (613)
12 (30) 113.1 (730)
13 (33) 132.7 (856)
14 (36) 153.9 (993)

1. The Air Temperature Rise is determined by subtracting the Return
Air Temperature Reading from the Supply Air Temperature Read-

DOWNFLOW
FURNACE

WARM AIR PLENUM
WITH 1” FLANGES

FIBERGLASS
INSULATION

ing.

2. The External Static Pressure is determined by adding the Supply
Duct Static Pressure reading to the Return Duct Static Pressure
reading and adding the pressure drop across any applied a-coil

FIBERGLASS TAPE
UNDER FLANGE

and return air filter.

Tables 2 and 3 are to be used as a guide only to help the installer deter­mine if the duct sizes are large enough to obtain the proper air flow

COMBUSTIBLE FLOOR
BASE ACCESSORY

(CFM) through the furnace. Tables 2 and 3 ARE NOT to be used to
design ductwork for the building where the furnace is being installed.
There are several variables associated with proper duct sizing that are

FIGURE 1: Combustible Floor Base Accessory

not included in the tables. To properly design the ductwork for the build­ing, refer to the ASHRAE Fundamentals Handbook, chapter on “DUCT
DESIGN” or a company that specializes in Residential and Modular

2

Unitary Products Group 5

268894-UIM-A-0407

The supply air temperature MUST NEVER exceed the Maximum
Outlet Air Temperature, specified on the nameplate.

Operating the furnace above the maximum outlet air temperature
will cause the heat exchanger to overheat, causing premature heat
exchanger failure. Improper duct sizing, dirty air filters, incorrect
manifold pressure, incorrect gas orifice and/or a faulty limit switch
can cause the furnace to operate above the maximum supply air
temperature. Refer to SECTIONS II, III and VIII for additional infor­mation on correcting the problem.

Downflow Air Conditioning Coil Cabinet

The furnace should be installed with coil cabinet part number specifi­cally intended for downflow application. If a matching cooling coil is
used, it may be placed directly on the furnace outlet and sealed to pre­vent leakage. For details of the coil cabinet dimensions and installation
requirements, refer to the installation instructions supplied with the coil
cabinet.

Attach the air conditioning coil cabinet to the duct connector, and then
position the furnace on top of the coil cabinet. The connection to the fur­nace, air conditioning coil cabinet, duct connector, and supply air duct
must be sealed to prevent air leakage.

IMPORTANT: On all installations without a coil, a removable access
panel is recommended in the outlet duct such that smoke or reflected
light would be observable inside the casing to indicate the presence of
leaks in the heat exchanger. This access cover shall be attached in
such a manner as to prevent leaks.

HORIZONTAL MODELS

Attach the supply plenum to the furnace outlet duct flanges through the
use of S cleat material when a metal plenum is used. The use of an
approved flexible duct connector is recommended on all installations.
This connection should be sealed to prevent air leakage. The sheet
metal should be cross-hatched to eliminate any popping of the sheet
metal when the indoor fan is energized. On all installations without a
coil, a removable access panel is recommended in the outlet duct such
that smoke or reflected light would be observable inside the casing to
indicate the presence of leaks in the heat exchanger. This access cover
shall be attached in such a manner as to prevent leaks.

Residential and Modular Home Horizontal Return Plenum
Connections

The return duct system must be connected to the furnace inlet and the
return duct system must terminate outside the space containing the fur­nace. When replacing an existing furnace, if the existing plenum is not
the same size as the new furnace then the existing plenum must be
removed and a new plenum installed that is the proper size for the new
furnace.

Attach the return plenum to the furnace inlet duct flanges. This is typi­cally through the use of S cleat material when a metal plenum is used.
The use of an approved flexible duct connector is recommended on all
installations. The connection of the plenum to the furnace and all the
ducts connecting to the plenum must be sealed to prevent air leakage.
The sheet metal should be cross-hatched to eliminate any popping of
the sheet metal when the indoor fan is energized.

The duct system is a very important part of the installation. If the duct
system is improperly sized the furnace will not operate properly. The
ducts attached to the furnace must be of sufficient size so that the fur­nace operates at the specified external static pressure and within the air
temperature rise specified on the nameplate.

Attic installations must meet all minimum clearances to combustibles
and have floor support with required service accessibility.

IMPORTANT: if an external mounted filter rack is being used see the
instructions provided with that accessory for proper hole cut size.

IMPORTANT: This furnace may be installed in a horizontal position on
either side as shown above. It must not be installed on its back.

Horizontal Installations With a Cooling Coil Cabinet

The furnace should be installed with coil cabinet part number specifi­cally intended for Horizontal application. If a matching cooling coil is
used, it may be placed directly on the furnace outlet and sealed to pre­vent leakage. Follow the coil instructions for installing the supply ple­num. For details of the coil cabinet dimensions and installation
requirements, refer to the installation instructions supplied with the coil
cabinet
Attach the supply plenum to the air conditioning coil cabinet outlet duct
flanges through the use of S cleat material when a metal plenum is
used. The use of an approved flexible duct connector is recommended
on all installations. The connection to the furnace, air conditioning coil
cabinet and the supply plenum should be sealed to prevent air leakage.
The sheet metal should be cross-hatched to eliminate any popping of
the sheet metal when the indoor fan is energized.
The minimum plenum height is 12” (30.5 cm). If the plenum is shorter
than 12” (30.5 cm) the turbulent air flow may cause the limit controls not
to operate as designed, or the limit controls may not operate at all. Also
the plastic drain pan in the air conditioning coil can overheat and melt.
Refer to the installation instructions supplied with the air conditioning
coil for additional information.

Horizontal Installations Without a Cooling Coil Cabinet

When installing this appliance, the furnace must be installed so as to
create a closed duct system, the supply duct system must be con­nected to the furnace outlet and the supply duct system must terminate
outside the space containing the furnace. When replacing an existing
furnace, if the existing plenum is not the same size as the new furnace
then the existing plenum must be removed and a new plenum installed
that is the proper size for the new furnace.

ATTIC INSTALLATION

12”

SUPPLY AIR

VENT (Maintain
required clearances
to combustibles)

SHEET METAL
IN FRONT OF
FURNACE
COMBUSTION AIR
OPENINGS IS
RECOMMENDED

LINE CONTACT ONLY PERMISSIBLE
BETWEEN LINES FORMED BY THE
INTERSECTION OF FURNACE TOP
AND TWO SIDES AND BUILDING
JOISTS, STUDS OR FRAMING

FILTER RACK
MUST BE A MINIMUM
DISTANCE
OF 18” (45.7 cm)
FROM THE
FURNACE

RETURN AIR

GAS PIPING

SEDIMENT

TRAP

12”

30” MIN.
WORK AREA

FIGURE 2: Typical Attic Installation

This appliance is design certified for line contact when the furnace is
installed in the horizontal left or right position. The line contact is only
permissible between lines that are formed by the intersection of the top
and two sides of the furnace and the building joists, studs or framing.
This line may be in contact with combustible material.

When a furnace is installed in an attic or other insulated space,
keep all insulating materials at least 12 inches (30.5 cm) away from
furnace and burner combustion air openings.

6 Unitary Products Group

SUSPENDED FURNACE / CRAWL SPACE
INSTALLATION

The furnace can be hung from floor joists or installed on suitable blocks
or pad. Blocks or pad installations shall provide adequate height to
ensure the unit will not be subject to water damage. Units may also be
suspended from rafters or floor joists using rods, pipe angle supports or
straps. Angle supports should be placed at the supply air end and near
the blower deck. Do not support at return air end of unit. All four sus­pension points must be level to ensure quiet furnace operation. When
suspending the furnace use a secure platform constructed of plywood
or other building material secured to the floor joists. Refer to Figure 3
for typical crawl space installation.

In any application where temperatures below freezing are possible,
see “INSTALLATION IN FREEZING TEMPERATURES” in SEC­TION I

268894-UIM-A-0407

ANGLE IRON
BRACKET

6” MIN. BETWEEN
ROD & FRONT OF FURNACE

1” MAX. BETWEEN
ROD & BACK OF FURNACE

FIGURE 3: Typical Suspended Furnace / Crawl Space Installation

SUPPORT
BRACKET

B

A

FRONT

20

3/4

40

B

1-7/8

D

FRONT

TOP IMAGE

5

20

T’STAT WIRING

7/8” K.O.

GAS INLET

1-1/4” X 2-1/2”

2-1/2

28-1/2

LEFT SIDE

4” Diameter

3-3/4

(VENT CONNECTION)

1-1/4

BOTTOM IMAGE

4” Diameter

20

FRONT

31-1/8

A

C

1-1/8

7-3/8

5-3/4

ALT. GAS INLET

1-1/4” X 2-1/2”

RIGHT SIDE

FIGURE 4: Dimensions
TABLE 4:

Cabinet and Duct Dimensions

BTUH (kW)

Input

CFM (m

Airflow

3

/min)

40 (11.7) 1200 (34.0) A 14 1/2 36.8 13 1/4 33.6 12 30.5 10 3/8 26.4
60 (17.6) 1200 (34.0) A 14 1/2 36.8 13 1/4 33.6 12 30.5 10 3/8 26.4
80 (23.4) 1200 (34.0) A 14 1/2 36.8 13 1/4 33.6 12 30.5 10 3/8 26.4
80 (23.2) 1600 (45.3) B 17 1/2 44.4 16 1/4 41.3 15 38.1 11-3/4 29.8

80 (23.2) 1600 (45.3) C 21 53.3 19 3/4 50.2 18-1/2 47.0 13 1/2 34.3
100 (29.3) 1200 (34.0) B 17 1/2 44.4 16 1/4 41.3 15 38.1 11 3/4 29.8
100 (29.3) 1600 (45.3) C 21 53.3 19 3/4 50.2 18-1/2 38.1 13 1/2 34.3
100 (29.3) 2000 (56.6) C 21 53.3 19 3/4 50.2 18-1/2 47.0 13 1/2 34.3
115 (33.7) 1600 (45.3) C 21 53.3 19 3/4 50 .2 18-1/2 47.0 13 1/2 34.3
115 (33.7) 2000 (56.6) C 21 53.3 19 3/4 50 .2 18-1/2 47.0 13 1/2 34.3
130 (38.1) 2000 (56.6) D 24 1/2 62.2 23 1/4 59.1 22 55.9 15 1/4 38.7

Unitary Products Group 7

Cabinet

Size

Cabinet Dimension

A A (cm) B B (cm) C C (cm) D D(cm)

268894-UIM-A-0407

RESIDENTIAL AND MODULAR HOME DOWNFLOW
RETURN PLENUM CONNECTION

The return duct system must be connected to the furnace inlet and the
return duct system must terminate outside the space containing the fur­nace. When replacing an existing furnace, if the existing plenum is not
the same size as the new furnace then the existing plenum must be
removed and a new plenum installed that is the proper size for the new
furnace.

Attach the return plenum to the furnace inlet duct flanges. This is typi­cally through the use of S cleat material when a metal plenum is used.
The use of an approved flexible duct connector is recommended on all
installations. The connection of the plenum to the furnace and all the
ducts connecting to the plenum must be sealed to prevent air leakage.
The sheet metal should be cross-hatched to eliminate any popping of
the sheet metal when the indoor fan is energized.

The duct system is a very important part of the installation. If the duct
system is improperly sized the furnace will not operate properly. The
ducts attached to the furnace must be of sufficient size so that the fur­nace operates at the specified external static pressure and within the air
temperature rise specified on the nameplate.

IMPORTANT: If an external mounted filter rack is being used see the
instructions provided with that accessory for proper hole cut size.

SECTION III: FILTERS

FILTER INSTALLATION

All applications require the use of an external filter. All filters and mount­ing provisions must be field supplied. Refer to Tables 5 & 16 for acces­sory External Filter Kits.
IMPORTANT: Air velocity through throwaway type filters must not

exceed 300 feet per minute (91 m/min). All velocities over this require
the use of high velocity filters. Refer to Table 14.

TABLE 5:

NOTES:

Recommended Filter Sizes

Cabinet Size Top Return (in) Top Return (cm)

A
B
C
D

1. Air velocity through throwaway type filters may not exceed 300 feet
per minute. All velocities over this require the use of high velocity fil­ters.

(2) 14 x 20 (2) 35.6 x 50.8
(2) 14 x 20 (2) 35.6 x 50.8
(2) 14 x 20 (2) 35.6 x 50.8
(2) 14 x 20 (2) 35.6 x 50.8

An overpressure protection device, such as a pressure regulator,
must be installed in the gas piping system upstream of the furnace
and must act to limit the downstream pressure to the gas valve so it
does not exceed 0.5 PSI (14" w.c. (3.48 kPa). Pressures exceeding

0.5 PSI (14” w.c. (3.48 kPa) at the gas valve will cause damage to
the gas valve, resulting in a fire or explosion or cause damage to
the furnace or some of its components that will result in property
damage and loss of life.

OUTLET
PRESSURE
PORT

INLET

WRENCH
BOSS

INLET
PRESSURE
PORT

OFF

ON

ON/OFF SWITCH
(Shown in ON position)

VENT PORT

OUTLET

MAIN REGULATOR
ADJUSTMENT

FIGURE 5: Gas Valve

GAS PIPING INSTALLATION

Properly sized wrought iron, approved flexible or steel pipe must be
used when making gas connections to the unit. If local codes allow the
use of a flexible gas appliance connection, always use a new listed con­nector. Do not use a connector that has previously serviced another gas
appliance.
Some utility companies or local codes require pipe sizes larger than the
minimum sizes listed in these instructions and in the codes. The fur­nace rating plate and the instructions in this section specify the type of
gas approved for this furnace - only use those approved gases. The
installation of a drip leg and ground union is required. Refer to Figures 6
& 7.

EXTERNAL MANUAL
SHUTOFF VALVE

TO GAS
SUPPLY

TO GAS
SUPPLY

HORIZONTAL APPLICATION

Horizontal Filters

All filters and mounting provisions must be field supplied. Filters(s) may
be located in the duct system external to the furnace or in a return filter
grille(s). Filters(s) may be located in the duct system using an external
duct filter box attached to the furnace plenum. Any branch duct (rectan­gular or round duct) attached to the plenum must attach to the vertical
plenum above the filter height. The use of straps and / or supports is
required to support the weight of the external filter box.

All installations must have a filter installed.

SECTION IV: GAS PIPING

GAS SAFETY

IMPORTANT: Plan your gas supply before determining the correct gas
pipe entry. Use 90-degree service elbow(s), or short nipples and con­ventional 90-degree elbow(s) to enter through the cabinet access holes.

8 Unitary Products Group

DRIP
LEG

GROUNDED JOINT UNION
MAY BE INSTALLED
INSIDE OR OUTSIDE UNIT.

FIGURE 6: Downflow Gas Piping

MANUAL
SHUT-OFF
VALV E

GAS
PIPE

GAS
PIPE

DRIP
LEG

FIGURE 7: Horizontal Gas Piping

DRIP
LEG

GAS BURNERS

GAS VALVE

MANUAL
SHUT-OFF VALVE

IMPORTANT: An accessible manual shut-off valve must be installed
upstream of the furnace gas controls and within six (6) feet (1.8 m) of
the furnace.

The furnace must be isolated from the gas supply piping system by
closing its individual external manual shut-off valve during any pressure
testing of the gas supply piping system at pressures equal to or less
than 1/2 psig (3.5 kPa).

Never apply a pipe wrench to the body of the gas valve when
installing piping. A wrench must be placed on the octagonal hub
located on the gas inlet side of the valve. Placing a wrench to the
body of the gas valve will damage the valve causing improper oper­ation and/or the valve to leak.

Gas piping may be connected from either side of the furnace using any
of the gas pipe entry knockouts on both sides of the furnace. Refer to
Figure 4 dimensions.

GAS ORIFICE CONVERSION FOR PROPANE (LP)

This furnace is constructed at the factory for natural gas-fired operation,
but may be converted to operate on propane (LP) gas by using a fac­tory-supplied LP conversion kit. Follow the instructions supplied with
the LP kit. Refer to Table 6 or the instructions in the propane (LP) con­version kit for the proper gas orifice size.

268894-UIM-A-0407

LoNOx furnaces requiring propane (LP) gas must have the LoNOx
screens removed prior to installation and operation. See the
instructions supplied with the propane conversion kit or the start up
procedure at the back of these instructions on proper removal of the
NOx screens.

HIGH ALTITUDE GAS ORIFICE CONVERSION

This furnace is constructed at the factory for natural gas-fired operation
at 0 – 8,000 feet (0-m – 2,438 m) above sea level.

The manifold pressure must be changed in order to manitain proper
and safe operation when the furnace is installed in a location where the
altitude is greater than 8,000 feet (2,438 m) above sea level. Refer to to
Table 6 for proper manifold pressure settings.

HIGH ALTITUDE PRESSURE SWITCH CONVERSION

For installation where the altitude is less than 8,000 feet (2,438 m), it is
not required that the pressure switch be changed. For altitudes above
8,000 feet (2,438 m), see Table 16 Field Installed Accessories - High
Altitude Pressure Switch.

TABLE 6:

PROPANE AND HIGH ALTITUDE CONVERSION KITS

It is very important to choose the correct kit and/or gas orifices for the altitude and the type of gas for which the furnace is being installed.
Only use natural gas in furnaces designed for natural gas. Only use propane (LP) gas for furnaces that have been properly converted to use pro-

pane (LP) gas. Do not use this furnace with butane gas.
Incorrect gas orifices or a furnace that has been improperly converted will create an extremely dangerous condition resulting in premature heat

exchanger failure, excessive sooting, high levels of carbon monoxide, personal injury, property damage, a fire hazard and/or death.
High altitude and propane (LP) conversions are required in order for the appliance to satisfactorily meet the application.
An authorized distributor or dealer must make all gas conversions.
In Canada, a certified conversion station or other qualified agency, using factory specified and/or approved parts, must perform the conversion.
The installer must take every precaution to insure that the furnace has been converted to the proper gas orifice size when the furnace is installed.
Do not attempt to drill out any orifices to obtain the proper orifice size. Drilling out a gas orifice will cause misalignment of the burner flames,
causing premature heat exchanger burnout, high levels of carbon monoxide, excessive sooting, a fire hazard, personal injury, property damage
and/or death.

Nominal Manifold Pressure - High Fire

Manifold Pressures (in wc) Manifold Pressures (kpa)

0-7999 8000-8999 9000-9999 0-2437 2438-2742 2743-3048
800 3.5 3.5 3.5
850 3.5 3.5 3.5 31.7 0.87 0.87 0.87
900 3.5 3.5 3.5 33.5 0.87 0.87 0.87
950 3.5 3.5 3.3 35.4 0.87 0.87 0.81

1000 3.5 3.2 2.9 37.3 0.87 0.80 0.73

(BTU/cu ft.)

Gas Heating Value

1050 3.5 2.9 2.7 39.1 0.87 0.73 0.67
1100 3.2 2.7 2.4 41.0 0.80 0.66 0.61

2500 (LP) 9.8 8.2 7.5 93.2 (LP) 2.44 2.03 1.86

Altitude (feet) Altitude (m)

29.8 0.87 0.87 0.87

(MJ/cu m)

Gas Heating Value

SECTION V: ELECTRICAL POWER

Electrical Power Connections

Field wiring to the unit must be grounded. Electric wires that are field
installed shall conform to the temperature limitation of 63°F (35°C) rise
when installed in accordance with these instructions. Refer to Table 7 in
these instructions for specific furnace electrical data.

Unitary Products Group 9

Use copper conductors only.