Lennox MERIT Series Installation Instructions Manual page 10

WARNING
Improper installation of the furnace can result in personal
injury or death. Combustion and flue products must
never be allowed to enter the return air system or air
in the living space. Use sheet metal screws and joint
tape to seal return air system to furnace. In platform
installations with furnace return, the furnace should be
sealed airtight to the return air plenum. A door must
never be used as a portion of the return air duct system.
The base must provide a stable support and an airtight
seal to the furnace. Allow absolutely no sagging, cracks,
gaps, etc. For no reason should return and supply air
duct systems ever be connected to or from other heating
devices such as a fireplace or stove, etc. Fire, explosion,
carbon monoxide poisoning, personal injury and/or
property damage could result.
The unit may be installed three ways in downflow applica-
tions: on non-combustible flooring, on combustible floor-
ing using an additive base, or on a reverse-flow cooling
coil cabinet. Do not drag the unit across the floor in the
downflow position. Floor and furnace flange damage
will result. Refer to FIGURE 13 for clearances in down-
flow applications.
Downflow Application Installation Clearances
Left Side
Top
*Front
Back
Sides
Vent
Floor
*Front clearance in alcove installation must be 24 in. (610 mm).
Maintain a minimum of 24 in. (610 mm) for front service access.
†Allow proper clearances to accommodate condensate trap and
vent pipe installation.
‡
tional base is installed between the furnace and the combustible
floor.
FIGURE 13
Top
Right Side
Bottom
0
0
0
0†
0
NC‡
Installation on Non-Combustible Flooring FIGURE 14
1 - Cut floor opening keeping in mind clearances listed
on unit rating plate. Also keep in mind gas supply
connections, electrical supply, flue and air intake
connections and sufficient installation and servicing
clearances. See TABLE 1 for correct floor opening
size.
2 - Flange warm air plenum and lower the plenum into
the opening.
3 - Set the unit over the plenum and seal the plenum to
the unit.
4 - Ensure that the seal is adequate.
NON-COMBUSTIBLE FLOOR OPENING SIZE
Cabinet
Width
B (17.5")
C (21")
NOTE - Floor opening dimensions listed are 1/4 inch (6 mm) larger than
the unit opening. See dimension drawing on page 2.
FURNACE
PROPERLY
SIZED FLOOR
OPENING
Installation on Combustible Flooring FIGURE 15
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.
Page 10
TABLE 1
Front to Rear Side to Side
in. mm in
19-3/4 502 16-5/8
19-3 4 502 20-1/8
SUPPLY AIR
PLENUM
FIGURE 14
CAUTION
mm
422
511