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Duct System and Filters
Duct System
The air handler is provided with flanges for the connection
of the plenum and ducts. The air handler is equipped with
flanges that can form a filter rack for the installation of the
air filter, or the filter may be installed as part of the return
air duct system.
Supply and return duct system must be adequately sized
to meet the system's air requirements and static pressure
capabilities. The duct system should be insulated with
a minimum of 1" thick insulation with a vapor barrier in
conditioned areas or 2" minimum in unconditioned areas.
Supply plenum should be the same size as the flanged
opening provided around the blower outlet and should
extend at least 3 ft. from the air handler before turning or
branching off plenum into duct runs. The plenum forms
an extension of the blower housing and minimizes air
expansion losses from the blower.
Filters
A filter is provided. Table 1 lists the filter size for each unit.
Capacity
Filter Size
-024 and -030
15" x 20" x 1
-036
18" x 20" x 1
-042, -048 and -060
18" x 24" x 1
IMPORTANT
If a high -efficiency filter is being installed as part of
this system to ensure better indoor air quality, the filter
must be properly sized. High -efficiency filters have a
higher static pressure drop than standard- efficiency
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 Allied Air
Product Specifications bulletin.
Page 10 of 22
Actual Minimum
Filter Size
14.50" x 19.50" x .75"
17.50" x 19.50" x .75"
17.50" x 23.50" x .75"
Table 1
Installing Duct System
Install the conditioned air plenum, ducts and air filters
(not provided) in accordance with NFPA 90B Standard for
the Installation of Warm Air Heating and Air-Conditioning
Systems (latest edition).
Connect supply air duct to the flange on top of the air
handler. If an isolation connector is used, it must be
nonflammable.
Field-Fabricated Return Air Duct Flange for
Horizontal Applications
A return air duct system is recommended, but not factory-
provided. If the unit is installed in a confined space or
closet, run a full-size return connection to a location outside
the closet.
CABINET
DOOR FLANGE
1−1/2
(38)
DUCT
FLANGE
3/4
(19)
1−1/2(38)
1/2
(13)
−024 & −030 18−3/8 (467)
−036 to −060 21−3/4 (552)
Figure 13. Cabinet and Duct Flange
Issue 1810
3/4
(19)
3/4
(19)
"A"
BRAKE DOWN 90 DEGREES
1/4 (6) DIA.
2−HOLES
"A"
UNIT SIZE
BOTTOM OF
CABINET
DUCT
ADAPTER
3/4
(19)
1−1/2
(38)
507623-02
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