Lennox SIGNATURE SL280UHV Installation Instructions Manual page 10

Return Air −− Upflow Applications
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.
NOTE −
60C and 60D units that require air volumes over 1800
cfm (850 L/s) must have one of the following:
1 − Return air from single side with transition which will
accommodate 20 x 25 x 1 in. (508 x 635 x 25 mm) clean-
able air filter. (Required to maintain proper air velocity.)
See figure 8.
2 − Return air from single side with optional RAB Return
Air Base. See figure 9.
3 − Return air from bottom and one side.
4 − Return air from both sides.
5 − Return air from bottom.
Refer to Engineering Handbook for additional information.
(Upflow Applications Only −− For use with A, B, C and D cabinets)
AIR FLOW
14−1/2" (368) A Width (65W75)
17−1/2" (446) B Width (50W98)
21"− (533) C Width (50W99)
24−1/2"− (622) D Width (51W00)
NOTE− Optional Side Return Air Filter Kits are not for use with Optional 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.
Optional Return Air Base
FURNACE
FRONT
IF BASE
IS USED
WITHOUT
IAQ CABINET,
INDOOR AIR
A SINGLE
RETURN AIR
PLENUM
MUST
COVER BOTH
UNIT AND
RETURN
AIR BASE
OPENINGS
OPTIONAL
RETURN AIR BASE
FIGURE 9
Page 10
Single Side Return Air
(with transition and filter)
AIR FLOW
FIGURE 8
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)
(Either Side)
26−7/8
(683)
SIDE VIEW
20" X 25" X 1"
(508mm X635mm X 25mm)
Cleanable Filter
Return Air
Plenum
Transition
1
Minimum
11 (279)
Maximum
2
1
22−7/16
14 (356)
(570)
Overall
(Maximum)
23
3/4
(584)
(19)