Check that adequate combustion air is available for the
furnace. Improper or insufficient combustion air can expose
building occupants to gas combustion products that could
include carbon monoxide. Refer to "Combustion and
Ventilation Air Requirements."
Set the furnace on a level floor to enable proper condensate
drainage. If the floor becomes wet or damp at times, place
the furnace above the floor on a concrete base sized
approximately 1¹⁄₂" (3.8 cm) larger than the base of the
furnace. Refer to "Horizontal Applications and
Considerations" for leveling of horizontal furnaces.
Check that the upflow or horizontal furnaces are not installed
directly on carpeting, or any other combustible material.
NOTE: The only combustible material allowed is wood.
A special accessory subbase must be used for the upright
counterflow unit installations over any combustible material
(including wood). Refer to subbase instructions for installation
NOTE: A subbase will not be required if an air conditioning
coil is located beneath the furnace between the supply air
opening and the combustible floor.
Exposure to contaminated combustion air will result in safety
and performance-related problems.
NOTE: Do not install the furnace where the combustion air is
exposed to the following substances:
Chlorinated waxes or cleaners
Chlorine-based swimming pool chemicals
Water softening chemicals
Deicing salts or chemicals
Cleaning solutions (such as perchloroethylene)
Cements and glues
Antistatic fabric softeners for clothes dryers
Masonry acid washing materials
Seal off a nondirect vent furnace if it is installed near an area
frequently contaminated by any of the above substances.
This protects the nondirect vent furnace from airborne
contaminants. To ensure that the enclosed nondirect vent
furnace has an adequate supply of combustion air, vent from
a nearby uncontaminated room or from outdoors. Refer to
"Combustion and Ventilation Air Requirements" for details.
If the furnace is used in connection with a cooling coil unit,
install the furnace upstream or in parallel with the cooling coil
unit. Premature heat exchanger failure will result if the cooling
coil unit is placed ahead of the furnace.
If the furnace is installed in a residential garage, position the
furnace so that the burners and ignition source are located
not less than 18" (45.7 cm) above the floor. Protect the
furnace from physical damage by vehicles.
If the furnace is installed horizontally, ensure the furnace
access doors are not on the "up/top" or "down/bottom" side
of the furnace. The furnace access doors must be vertical so
that the burners fire horizontally into the heat exchanger.
Do not connect the furnace to a chimney flue that serves a
separate appliance designed to burn solid fuel.
On counterflow installations, the air conditioning coil must be
downstream on the supply (positive) side of the furnace heat
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.
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 floor.
Clearances and Accessibility
Installations must adhere to the clearances to combustible
materials to which this furnace has been design-certified. The
minimum clearance information for this furnace is provided on
the unit's clearance label. These clearances must be permanently
Clearances must also accommodate an installation's gas,
electrical, drain trap and drain line connections. If the alternate
vent/flue connection is used, additional clearance must be
provided to accommodate these connections. Refer to "Vent/
Flue Pipe and Combustion Air Pipe" for details.
NOTE: In addition to the required clearances to combustible
materials, a minimum of 24" (61 cm) service clearance must be
available in front of the unit.
A furnace installed in a confined space (for example, a closet or
utility room) must have 2 ventilation openings with a total
minimum free area of 0.25 sq. in. per 1,000 Btu/h of furnace input
rating. Refer to the Specification Sheet applicable to your model
for minimum clearances to combustible surfaces. One of the
ventilation openings must be within 12" (30.5 cm) of the top. The
other opening must be within 12" (30.5 cm) of the bottom of the
confined space. In a typical construction, the clearance between
the door and door frame is usually adequate to satisfy this
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 "Suspended Furnace" illustration. The length of rod will
depend on the application and the clearances necessary.