Lennox SL280UHNV 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 cab-
inet for installations that require side return air. Cut the
furnace cabinet at the maximum dimensions shown on
page 2.
NOTE - 60C units that require air volumes over 1800
cfm (850 L/s) must have one of the following:
1 - Single side return air and optional return air
base with transition which will accommodate 20
x 25 x 1 in. (508 x 635 x 25 mm) air filter. (Re-
quired to maintain proper air velocity.
2 - Bottom return air
3 -Return air from both sides.
4 -Return air from bottom and one side.
Refer to Engineering Handbook for additional information.
AIR FLOW
14−1/2" (368) A Width (65W75)
17−1/2" (446) B Width (50W98)
21"− (533) C Width (50W99)
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
(Upflow Applications Only -- For use with A, B and C cabinets)
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
Single Side Return Air
(with transition and filter)
AIR FLOW
3−1/4
(83)
1
Unit side return air
5−5/8
7−1/4
(143)
(184)
FIgURE 10
Page 10
20" X 25" X 1"
(508mm X635mm X 25mm)
Cleanable Filter
Return Air
Plenum
Transition
FIgURE 9
1
23 (584)
Overall
1
(Maximum) Minimum
11 (279)
Maximum
2
14 (356)
Opening
SIDE RETURN
AIR OPENINGS
(Either Side)
23
(584)
26−7/8
(683)
SIDE VIEW
1
22−7/16
(570)
Overall
(Maximum)
3/4
(19)