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2.5. MMA Indoor Unit Clearances
Non-Ducted Return Closet Installation
The air handler can be installed in a closet with a false bot-
tom to form a return air plenum. It may also be installed with
a return air plenum under the air handler. Louvers or return
air grilles are eld-supplied. Local codes may limit applica-
tion of systems without a ducted return to single-story build-
ings.
Minimum Open Area for Louvers
When an air handler unit is installed in a closet with a lou-
vered return opening, use the following table to determine
the minimum open area for the louvers:
Model Minimum Open Area
018, 024 320 square inches
036 360 square inches
048 - 060 450 square inches
If the free area is not known, assume a 25% free area for
wood or a 75% free area for metal louvers or grilles. Us-
ing the louver dimensions and the 25% or 75% assumption,
determine if the open area meets the minimum open area
listed above.
Figure 2. Plenum Clearance (Horizontal Installation)
If a 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 ow of return air. When not installed in front of the
opening, there must be adequate clearance around the air
handler to allow for the free ow of return air.
Plenum Clearance
The outlet side pipe length is 4.9 ft (1.5m) There should be a
clearance of 1 in. (25.4mm) on all sides of the plenum.
Vertical Installation (Ducted)
When installed vertically (upward or downward), the lower
end of the air outlet must be connected to the L-shaped met-
al air duct and fastened by screws.
Figure 3. Air Handler (Shown in Vertical Installation
with L-Shape Duct)
Minimum Clearance of 1 inch
(25.4 mm) on all sides
Flexible Duct Colllar
4.9 ft (1.5m)
Or
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