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Return Air Opening - Downflow Units
Return air may be brought in only through the top opening of
a furnace installed in the downflow position. The following
steps should be taken when installing plenum:
1.
Bottom edge of plenum should be flanged with a
hemmed edge (See Figure 11 or Figure 12).
2.
Sealing strips should be used to ensure an airtight
seal between the cabinet and the plenum.
3.
In all cases, plenum should be secured to top of
furnace using sheet metal screws.
4.
Make certain that an adequate seal is made.
Figure 11.
Figure 12.
Filters
This unit is not equipped with a filter or rack. A field provided
filter is required for the unit to operate properly. Table 3 lists
recommended filter sizes.
A filter must be in place when the unit is operating!
Furnace Cabinet Width
B Cabinet 17-1/2"
C Cabinet 21"
507029-05
Minimum Filter Size
Side Return
16 x 25 x 1 (1)
Table 3.
Duct System
Use industry approved standards to size and install the
supply and return air duct system. This will result in a quiet
and low static system that has uniform air distribution.
NOTE: Operation of this furnace in heating mode (indoor
blower operating at selected heating speed) with an
external static pressure which exceeds 0.8 inches w.c.
may result in erratic limit operation.
Supply Air Plenum
If the furnace is installed without a cooling coil, a removable
access panel should be installed in the supply air duct. The
access panel should be large enough to permit inspection
(by reflected light) of the heat exchanger for leaks after
the furnace is installed. If present, this access panel must
always be in place when the furnace is operating and it
must not allow leaks into or from the supply air duct system.
Return Air Plenum
Return air must not be drawn from a room where this
furnace, or any other gas fueled appliance (i.e., water
heater), or carbon monoxide producing device (i.e., wood
fireplace) is installed. When return air is drawn from a
room, a negative pressure is created in the room. If a gas
appliance is operating in a room with negative pressure, the
flue products can be pulled back down the vent pipe and
into the room. This reverse flow of the flue gas may result
in incomplete combustion and the formation of carbon
monoxide gas. This toxic gas might then be distributed
throughout the house by the furnace duct system.
Pipe and Fittings Specifications
All pipe, fittings, primer and solvent cement must conform
with American National Standard Institute and the American
Society for Testing and Materials (ANSI/ASTM) standards.
The solvent shall be free flowing and contain no lumps,
undissolved particles or any foreign matter that adversely
affects the joint strength or chemical resistance of the
cement. The cement shall show no gelation, stratification,
or separation that cannot be removed by stirring. Refer to
Table 4 for approved piping and fitting materials.
Issue 2241
Page 9 of 73
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