20
or suspended furnaces closer than 12--in. (305 mm) to joists. The
sheet metal MUST extend underneath the furnace casing by 1 -- in.
(25 mm) with the door removed.
The bottom closure panel on furnaces of widths 17--1/2--in. (445
mm) and larger may be used for flame roll--out protection when
bottom of furnace is used for return air connection. See Fig. 25 for
proper orientation of roll--out shield.
ANY COMBINATION OF 1, 2, OR 3 PERMITTED.
A11036
Fig. 22 -- Upflow Return Air Configurations and Restrictions
A11037
Fig. 23 -- Downflow Return Air Configurations
and Restrictions
HORIZONTAL TOP
RETURN NOT
PERMITTED FOR
ANY MODEL
A11038
Fig. 24 -- Horizontal Return Air Configurations
and Restrictions
Supply Air Connections
For a furnace not equipped with a cooling coil, the outlet duct shall
be provided with a removable access panel. This opening shall be
accessible when the furnace is installed and shall be of such a size
that the heat exchanger can be viewed for possible openings using
light assistance or a probe can be inserted for sampling the air
stream. The cover attachment shall prevent leaks.
Connect supply--air duct to flanges on furnace supply--air outlet.
Bend flange upward to 90_ with wide duct pliers. See Fig. 19.
The supply--air duct must be connected to ONLY the furnace
supply-- outlet--air duct flanges or air conditioning coil casing
(when used). DO NOT cut main furnace casing side to attach
supply air duct, humidifier, or other accessories. All supply-- side
accessories MUST be connected to duct external to furnace main
casing.
Return Air Connections
The return--air duct may be connected to bottom of the furnace.
The side of casing that faces downward may also be used for return
air connection. A combination of the bottom and downward
facing side may also be used. The upward facing side of the casing
cannot be used as a return air connection. See Fig. 24.
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