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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 FIGURE 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
furnace using sheet metal screws.
4 - Make certain that an adequate seal is made.
PLENUM
(Field Provided)
SEALING STRIP
(Field Provided)
Side View
FIGURE 11
PLENUM
(Field Provided)
SECURE FROM
INSIDE CABINET
Side View
FIGURE 12
Filters
This unit is not equipped with a filter or rack. A field-provid-
ed 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.
IMPORTANT
If a highefficiency filter is being installed as part of this
system to ensure better indoor air quality, the filter must
be properly sized. Highefficiency filters have a higher
static pressure drop than standardefficiency glass/foam
filters. If the pressure drop is too great, system capacity
and performance may be reduced. The pressure drop
may also cause the limit to trip more frequently during
the winter and the indoor coil to freeze in the summer,
resulting in an increase in the number of service calls.
Before using any filter with this system, check the
specifications provided by the filter manufacturer against
the data given in the appropriate Lennox Product
Specifications bulletin. Additional information is provided
in Service and Application Note ACC002 (August 2000).
SECURE FROM
OUTSIDE CABINET
CABINET
SIDE PANEL
SEALING STRIP
(Field Provided)
CABINET
SIDE PANEL
Page 9
TABLE 3
Furnace Cabinet Width
B Cabinet 17-1/2"
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 qui-
et and low-static system that has uniform air distribution.
See FIGURE 13 below for proper duct installation.
Duct Installation
Down-Flow Unit
FIGURE 13
Discharge Air Temperature Sensor
This furnace is shipped with a discharge air temperature
sensor that can be installed in the furnace plenum. The
sensor is used to measure temperature rise in the heat-
ing mode and temperature drop in the cooling mode. See
TABLE 4 and FIGURE 14. Drill a 3/8 inch diameter hole
in the plenum based on the specified location. Center the
discharge air temperature sensor in the middle of the hole
and use two field provided screws to secure in place. Field
supplied wiring must be used to connect the sensor to the
discharge air temperature sensor terminals on the inte-
grated control board. See FIGURE 14.
NOTE - If unable to mount at specified location, sensor
can be mounted in the coil cabinet 1" from the bottom and
5" from the right side. Care must be exercised to avoid
hitting the coil/drainpan while drilling through the cabinet.
A communicating thermostat can be used to run tempera-
ture rise and temperature drop tests and viewed in the
installation reports. See FIGURE 48 on page 36 for
thermostat wiring. If a communicating thermostat is not
being used, then the discharge air temperature can be
viewed on the seven segment LED on the integrated con-
trol shown in FIGURE 14.
For zoning applications the discharge air sensor must be
installed and wired to the zoning control board. Wiring to
the furnace control board is not required.
Fillter Size
16 X 25 X 1 (1)
SUPPLY
AIR
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