507714-01
Page 11 of 52
Issue 1716
Figure 15.
SUPPLY AIR
PLENUM
PROPERLY
SIZED FLOOR
OPENING
FURNACE
NON-COMBUSTIBLE
FLOORING
Installation on Combustible Flooring
1. When unit is installed on a combustible floor, a
downflow combustible flooring base must be installed
between the furnace and the floor. The base must be
ordered separately. See Table 2 for opening size to
cut in floor.
The furnace and combustible flooring base shall not be
installed directly on carpeting, tile, or other combustible
material other than wood flooring.
CAUTION
Table 2. Combustible Flooring Base Opening Size
Cabinet
Width
Catalog
Number
Front to Rear
Side to Side
in.
mm
in.
mm
B cabinet
(17.5”)
11M60
22
559
18-3/4
476
C cabinet
(21”)
11M61
22
559
22-3/4
578
Figure 16.
FURNACE
SUPPLY AIR
PLENUM
COMBUSTIBLE
FLOORING BASE
PROPERLY
SIZED FLOOR
OPENING
COMBUSTIBLE
FLOORING
2. After opening is cut, set the combustible flooring base
into opening.
3. Check fiberglass strips on the combustible flooring
base to make sure they are properly glued and
positioned.
4. Lower supply air plenum into the combustible flooring
base until plenum flanges seal against fiberglass
strips.
NOTE:
Be careful not to damage fiberglass strips.
Check for a tight seal.
5. Set the furnace over the plenum.
6. Ensure that the seal between the furnace and plenum
is adequate.
Installation on Cooling Coil Cabinet
NOTE:
Downflow combustible flooring kit is not used.
1. Refer to reverse-flow coil installation instructions for
correctly sized opening in floor and installation of
cabinet.
2. When cooling cabinet is in place, set and secure the
furnace according to the instructions that are provided
with the cooling coil. Secure the furnace to the cabinet.
3. Seal the cabinet and check for air leaks.
Figure 17.
Return Air Opening - Downflow Units
Return air may be brought in only through the top opening of
a furnace installed in the downflow position. The following
steps should be taken when installing plenum:
1. Bottom edge of plenum should be flanged with a
hemmed edge (see Figure 18 or Figure 19).
2. Sealing strips should be used to ensure an airtight
seal between the cabinet and the plenum.