# 44876D006 Page 3
Supply and return ductwork must be adequately sized to
meet the system’s air requirements and static pressure
capabilities. Ductwork should be insulated with a minimum
of 1" thick insulation with a vapor barrier in conditioned
areas or 2" minimum in unconditioned areas. Connect
supply air duct to the flange on top of the unit. If an
isolation connector is used, it must be non-flammable.
Sheet metal ductwork run in unconditioned spaces must
be insulated and covered with a vapor barrier. Fibrous
ductwork may be used if constructed and installed in
accordance with SMACNA Construction Standard on
Fibrous Glass Ducts. Check local codes for requirements
on ductwork and insulation.
Duct system must be designed within the range of exter-
nal static pressure the unit is designed to operate against.
It is important that the system airflow be adequate. Make
sure supply and return ductwork, grills, special filters,
accessories, etc. are accounted for in total resistance.
Supply plenum is attached to the duct flanges supplied on
the unit around the blower outlet.
Supply plenum should be the same size as the flanged
opening provided around the blower outlet and should
extend ideally at least 3' from the unit before turning or
branching off plenum into duct runs. The plenum forms an
extension of the blower housing and minimizes air expan-
sion losses from the blower.
If an elbow is included in the plenum close to the unit,
it must not be smaller than the dimensions of the
supply duct flange on the unit.
Non-Ducted Return Closet Installation
The cabinet can be installed in a closet with a false bottom
to form a return air plenum or be installed with a return air
plenum under the unit. Louvers or return air grilles are
field supplied. Local codes may limit application of sys-
tems without a ducted return to single story buildings.
• Install louvers in a closet. Use the free area of louver
or grille to determine the size opening required to
provide the free area for metal louvers or grilles.
• If the free area is not known, assume a 25% free area
for wood or a 75% free area for metal louvers or grilles.
• If the return air plenum is used, the return air grille
should be immediately in front of the opening in the
plenum to allow for the free flow of return air.
• When not installed in front of the opening, there must
be adequate clearance around the unit to allow for the
free flow of return air.
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Recommended Remote Filter Sizes
Table 1
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