506550-01 Page 11 of 66Issue 1230
Return Air - Horizontal Applications
Return air must be brought in through the end of a furnace
installed in the horizontal position. The furnace is equipped
with a removable bottom panel to facilitate installation. See
Figure 7.
Filters
This unit is not equipped with a filter or rack. A field provided
filter is required for the unit to operate properly. Table 1 lists
recommended filter sizes.
A filter must be in place when the unit is operating!
NOTE: In upflow applications where side return air filter is
installed on same side as the condensate trap, make sure
that clearance is maintained to ensure future access to the
filter access panel.
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.
Return air can be brought in through the bottom or either
side of the furnace. If a furnace with bottom return air is
installed on a platform, make an airtight seal between the
bottom of the furnace and the platform to ensure that the
unit operates properly and safely. Use fiberglass sealing
strips, caulking, or equivalent sealing method between the
plenum and the furnace cabinet to ensure a tight seal. If a
filter is installed, size the return air duct to fit the filter frame.
Figure 13
* Gas Connector may be used for Canadian installation if acceptable
by local authority having jurisdiction.
Table 1
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