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Page 9
FIGURE 10
COOLING COIL
PLENUM
PROPERLY
SIZED FLOOR
OPENING
SLP98DF UNIT
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 follow-
ing steps should be taken when installing plenum:
1 − Bottom edge of plenum should be flanged with a
hemmed edge (See figure 11 or 12).
2 − Sealing strips should be used to ensure an airtight seal
between the cabinet and the plenum.
3 − In all cases, plenum should be secured to top of fur-
nace using sheet metal screws.
4 − Make certain that an adequate seal is made.
FIGURE 11
SECURE FROM
OUTSIDE CABINET
PLENUM
(Field Provided)
SEALING STRIP
(Field Provided)
Side View
CABINET
SIDE PANEL
SECURE FROM
INSIDE CABINET
PLENUM
(Field Provided)
SEALING STRIP
(Field Provided)
Side View
CABINET
SIDE PANEL
FIGURE 12
Filters
This unit is not equipped with a filter or rack. A field−pro-
vided filter is required for the unit to operate properly. Table
3 lists recommended filter size.
A filter must be in place whenever the unit is operating.
TABLE 3
Furnace
Cabinet Width
Filter Size
B Cabinet (17−1/2")
16 X 25 X 1 (1)
C Cabinet (21−1/2")
Duct System
Use industry-approved standards to size and install the
supply and return air duct system. This will result in a quiet
and low-static system that has uniform air distribution.
NOTE − Operation of this furnace in heating mode (indoor
blower operating at selected heating speed) with an exter-
nal static pressure which exceeds 0.8 inches w.c. may re-
sult in erratic limit operation.
Return Air Plenum
Return air must not be drawn from a room where this
furnace, or any other gas−fueled appliance (i.e., water
heater), or carbon monoxide−producing device (i.e.,
wood fireplace) is installed. When return air is drawn
from a room, a negative pressure is created in the room. If
a gas appliance is operating in a room with negative pres-
sure, the flue products can be pulled back down the vent
pipe and into the room. This reverse flow of the flue gas
may result in incomplete combustion and the formation
of carbon monoxide gas. This toxic gas might then be dis-
tributed throughout the house by the furnace duct sys-
tem.
Use fiberglass sealing strips, caulking, or equivalent seal-
ing method between the plenum and the furnace cabinet to
ensure a tight seal. If a filter is installed, size the return air
duct to fit the filter frame.