The 45,000 and 67,000 Btu/h models contain an inlet air
assembly that uses two 22.5° elbows that attach separately
from the straight inlet pipe, as shown. This allows the inlet
pipe assembly to be removed if needed for service.
Install ductwork in accordance with NFPA 90B and any local
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 to avoid a negative pressure on the venting
Installation with Return Ducts
A return air duct system is recommended. If the furnace is
installed in a confined space or closet, a return connection must
be run, full size, to a location outside the closet. The air duct in
the closet must be tight to avoid any entrance of air from the
closet into the circulating air.
Some model furnaces can be installed with either a side or
bottom air return. For bottom air return the bottom air return
knockout plate must be removed. For units that do not include a
side or bottom return filter rack, kit no. AFILT524-1 (side return) or
kit no. AFILT529-1 (bottom return) can be used.
To provide sufficient filter area for installations requiring more
than 1,600 CFM nominal air delivery, return air will have to be
brought through both sides of the furnace, or through one side
and the bottom, or an optional filter rack WAFILTHA7 may be
Inlet Air Assembly—45,000 & 67,000 Btu/h Units
Installation with an Evaporator Coil
When an air conditioning furnace is used in conjunction with the
furnace, the evaporator coil must be installed in the discharge
(supply) air. Do not install an evaporator coil in the return air;
excessive condensation will occur within the furnace.
Installation without an Evaporator Coil
If a cooling coil is not installed with the furnace, then a removable
access panel should be provided in the supply plenum for
purposes of inspecting the heat exchanger. This opening must be
accessible when the furnace is installed. It must be large enough
that the heat exchanger can be viewed for possible openings
using light assistance or so that a probe can be inserted for
sampling the airstream. The cover for the opening must be
Filters are not supplied with these furnaces; however, filters must
be used. It is the installer's responsibility to install a filter rack with
the ductwork and to install properly sized filters in accordance
with the Minimum Filter Requirements Chart.
The Airflow Descriptor is the 2 digits immediately preceding
the hyphen (-) in the furnace model number. The model
number is located on the rating plate inside the access panel.
Areas and dimensions shown for cleanable filters are based
on filters rated at 600 ft (182.9 m) per minute face velocity.
A. Straight inlet pipe
C. Burner box
B. 22.5° elbows