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- Elbows with turning vanes or splitters are
recommended to minimize air noise and resistance;
- The first elbow in the ductwork leaving the unit
should be no closer than 3 fan diameters from the
unit, thereby minimizing noise and resistance.
In those instances where the unit is installed over an
acoustically critical area, additional treatment of the
ductwork is recommended. Both supply and return
Figure 20
Typical Supply and Return Ductwork
3 Fan
diameters
8
ductwork should be lined internally with glass fiber
duct liner 1" thick. The external surface of the supply
duct should be covered with an acoustical barrier
material such as one or two pound/sq. ft. sheet lead
(1/64" or 1/32") or loaded vinyl sheet or gypsum
board for the first 10 ft. of ductwork. The lining should
extend from the point where the duct penetrates the
roof to a distance of 10 ft. beyond the vertical drop
from the unit.
Coil
space
Vertical
discharge
Use line duct for all returns
(1" thick, 6 lb density fiberglass recommended)
Return air
CLCH-IN-18A
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