On counterflow installations, the air conditioning coil must be
downstream from the furnace heat exchanger.
Counterflow Installation Over a Noncombustible Floor
Before setting the furnace over the plenum opening, ensure
that the surface around the opening is smooth and level. A
tight seal should be made between the furnace base and
floor by using a silicone rubber caulking compound or
Counterflow Installation Over a Combustible Floor
If installation over a combustible floor becomes necessary, use
an accessory subbase (see Specification Sheet applicable for
your model for details). A special accessory subbase must be
used for upright counterflow unit installations over any
combustible material, including wood. Refer to subbase
instructions for installation details. Follow the instructions with
the subbase for proper installation.
NOTE: Do not install the furnace directly on carpeting, tile or
other combustible material other than wood flooring.
The subbase will not be required if an air conditioning coil is
installed between the supply air opening on the furnace and the
Clearances and Accessibility
Unobstructed front clearance of 24" (61 cm) for servicing is
Clearances to Combustibles—in. (cm)
Connector Sides Front Back Top (Plenum)
NOTE: Top clearance for horizontal configuration is 1" (2.5 cm).
A. Top clearance—1" (2.5 cm)
B. Vent pipe clearance—6" (15.2 cm)
for single wall connector, 1"
(2.5 cm) for B-1 vent
Adequate combustion/ventilation air must be supplied to the
closet or enclosure.
Furnace must be completely sealed to the floor or base.
Combustion/ventilation air supply pipes must terminate 12"
(30.5 cm) from the top of the closet or enclosure and 12"
(30.5 cm) from the floor of the closet or enclosure.
C. Back clearance—0"
D. Side clearance—1" (2.5 cm)
E. Front clearance—3" (7.6 cm)
NOTE: Do not remove the solid base plate for the side return.
Return air ducts must be completely sealed to the furnace
and terminate outside the enclosure surfaces.
Horizontal Installation—WGFM28 Models Only
Line contact to framing is permitted when installed in the
horizontal configuration. Line contact is defined as the portion of
the cabinet that is formed by the intersection of the top and side.
IMPORTANT: Accessibility clearance, where greater, should take
precedence over minimum fire protection clearance.
A gas-fired furnace for installation in a residential garage
must be installed so that the ignition source and burners are
located not less than 18" (45.7 cm) above the floor and are
protected or located to prevent physical damage by vehicles.
A gas furnace must not be installed directly on carpeting, tile,
or other combustible materials other than wood flooring.
If suspending the furnace from rafters or joists, use ³⁄₈" threaded
rod and 2" x 2" x ¹⁄₈" (5.1 cm x 5.1 cm x 3.2 mm) angle iron as
shown in the "Suspended Furnace" illustration. The length of the
rod will depend on the application and the clearances necessary.
A. ³⁄₈ " (1 cm) diameter threaded
B. 8" (20.3 cm) minimum clearance
between center rod and furnace
cabinet to allow for circulator
C. Level furnace end to end, slight
forward tilt with front 0" to ³⁄₄ "
(1.9 cm) below back.
NOTE: When an existing furnace is removed from a venting
system serving other appliances, the venting system may be too
large to properly vent the remaining attached appliances.
The following vent testing procedure is reproduced from the
American National Standard/National Standard of Canada for
Gas-Fired Central Furnaces ANSI Z21.47—latest edition,
CSA-2.3—latest edition Section 1.23.1.
The following steps shall be followed with each appliance
connected to the venting system placed in operation, while any
other appliances connected to the venting system are not in
1. Seal any unused openings in the venting system.
2. Inspect the venting system for proper size and horizontal
pitch, as required by the National Fuel Gas Code, ANSI
Z223.1 or the CAN/CSA B149 Installation Codes and these
instructions. Determine that there is no blockage or
restriction, leakage, corrosion and other deficiencies which
could cause an unsafe condition.
D. Tilt outward to allow for door and
circulator blower removal.
E. Position as close as possible to
blower deck to allow for
circulator blower removal.
F. 2" x 2" x ¹⁄₈ " (5.1 cm x 5.1 cm x
3.2 mm) angle iron (3)
G. Support nuts
H. Hold down nuts
Existing Furnace Removal