Page 12
80AF1DF UNIT
COOLING COIL
PLENUM
FIGURE 12
PROPERLY
SIZED FLOOR
OPENING
Return Air Opening −− Downflow Units
The following steps should be taken when installing ple-
num:
1 − Bottom edge of plenum should be flanged with a
hemmed edge (See figure 13).
SECURE FROM
OUTSIDE CABINET
HEMMED EDGE
PLENUM
SEALING STRIP
(Field Provided)
CABINET SIDE PANEL
Side View
FIGURE 13
2 − Sealing strip should be used.
3 − In all cases, plenum should be secured to top flanges
of furnace with sheet metal screws.
SECURE FROM IN-
SIDE CABINET
HEMMED EDGE
FIBERGLASS
SEALING STRIP
(Field Provided)
CABINET SIDE
PANEL
PLENUM
Side View
FIGURE 14
4 − In closet installations, it may be impossible to install
sheet metal screws from the outside. In this case,
make plenum with a removable front and install
screws from the inside (See figure 14).
5 − Make certain that an adequate seal is made.
Filters
This unit is not equipped with a filter or rack. A field−pro-
vided high−velocity filter is required for the unit to operate
properly. Table 3 lists recommended filter sizes.
A filter must be in place any time the unit is operating.
TABLE 3
Cabinet Width
Return Air Filter Size (inches)
A (14−1/2")
14 x 25 x 1 (1)
B (17−1/2")
16 x 25 x 1 (1)
C (21")
20 x 25 x 1 (1)
Duct Sytem
Use industry-approved standards (such as those pub-
lished by Air Conditioning Contractors of America or Ameri-
can Society of Heating, Refrigerating and Air Conditioning
Engineers) 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 − Do not operate the furnace in the heating mode
with an external static pressure that exceeds 0.8 inches
w.c. Higher external static pressures may cause erratic lim-
it operation.
Ensure that you have made a seal between the supply air
plenum and the furnace and between the furnace and the
return air plenum.
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.
