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Return Air Guidelines
Return air can be brought in through the bottom or either
side of the furnace installed in an upflow application. If the
furnace is installed on a platform with bottom return, make
an airtight seal between the bottom of the furnace and the
platform to ensure that the furnace operates properly and
safely. The furnace is equipped with a removable bottom
panel to facilitate installation.
Markings are provided on both sides of the furnace cabinet
for installations that require side return air. Cut the furnace
cabinet at the maximum dimensions shown on Page 2.
Furnace applications which include side return air and a
condensate trap installed on the same side of the cabinet
(trap can be installed remotely within 5 ft.) require either a
return air base or field-fabricated transition to accommodate
an optional IAQ accessory taller than 14.5". See Figure 14.
CONDENSATE
TRAP
AIR FLOW
17−1/2 (446) B Width (68W62)
21 (533) C Width (68W63)
FRONT VIEW
NOTE: Optional side return air filter kits are not for use with return air base.
1 Both the unit return air opening and the base return air opening must be covered by a single plenum or IAQ cabinet.
Minimum unit side return air opening dimensions for units requiring 1800 cfm or more of air (W x H): 23 x 11 in. (584 x 279 mm).
The opening can be cut as needed to accommodate plenum or IAQ cabinet while maintaining dimensions shown.
Side return air openings must be cut in the field. There are cutting guides stenciled on the cabinet for the side return air opening.
The size of the opening must not extend beyond the markings on the furnace cabinet.
2 To minimize pressure drop, the largest opening height possible (up to 14 inches) is preferred.
507768-05G / 31-5000655
FURNACE
FRONT
IF BASE
IS USED
WITHOUT
IAQ CABINET,
INDOOR AIR
A SINGLE
QUALITY
RETURN AIR
CABINET
PLENUM
MUST
(PCO, Filter
COVER BOTH
Cabinet, etc.)
UNIT AND
RETURN
AIR BASE
OPENINGS
OPTIONAL
RETURN
AIR BASE
Figure 15. Optional Return Air Base
(Upflow Applications Only)
Issue 2223
Transition
Figure 14. Side Return Air
(with Transition and Filter)
1
23 (584)
3−1/4
Overall
(83)
(Maximum)
1
Unit side return air
Opening
SIDE RETURN
5−5/8
7−1/4
AIR OPENINGS
(143)
(184)
26−7/8
(683)
SIDE VIEW
20" X 25" X 1"
(508mm X 635mm X 25mm)
Air Filter
Return
Air
Plenum
1
Minimum
11 (279)
Maximum
2
1
22−7/16
14 (356)
Overall
(Maximum)
(Either Side)
23
(584)
Page 11 of 56
(570)
3/4
(19)
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