A sound attenuating transfer duct is a duct used to allow air to flow through a sound wall, but not sound. It is a necessity in buildings that have a return air plenum and full-height sound walls.
The duct should be constructed according to SMACNA HVAC Duct Construction Standards with no turning vanes in the elbows.
Line duct with 1” thick fiberglass with a coated surface equal to Johns Manville Linacoustic RC.
I typically layout transfer air ducts to provide multiple parallel paths of airflow from each space back to the air handling unit return air duct. This minimizes pressure drop and provides for a good air balance.
Dimensions H and W are the clear dimensions from liner surface to liner surface. H and W are calculated as required to achieve an airflow velocity of approximately 500 fpm (HxW=CFM/500). H may be limited by space constraints in the plenum.
Dimension A should be equal to or greater than W.
Dimension B should be equal to or greater than 1.5 x W.
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