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Figure 12.
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 13 or Figure 14).
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 13.
Figure 14.
507332-02G / 31-5000663
Filters
This unit is not equipped with a filter or rack. A field provided
high velocity filter is required for the unit to operate properly.
A filter must be in place any time the unit is operating.
Duct System
Use industry approved standards (such as those published
by Air Conditioning Contractors of America or American
Society of Heating, Refrigerating and Air Conditioning
Engineers) 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: Do not operate the furnace in the heating mode
with an external static pressure that exceeds 0.8 inches
w.c. Higher external static pressures may cause erratic
limit operation.
Supply Air Plenum
If the furnace is installed without a cooling coil, a removable
access panel must be installed in the supply air duct. The
access panel should be large enough to permit inspection
(either by smoke or reflected light) of the heat exchanger
for leaks after the furnace is installed. The furnace access
panel must always be in place when the furnace is operating
and it must not allow leaks into the supply air duct system.
Return Air Plenum
NOTE: 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.
Venting
A 4 inch diameter flue transition is factory installed on the
combustion air inducer outlet of all models.
Issue 2209
Page 11 of 35
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