Setting a Barometric Bypass Damper

General Instructions for Residential and Light Commercial Barometric Bypass Dampers


As the individual zone dampers close, the system static pressure will tend to rise.  In order to maintain constant airflow through the HVAC system, a barometric bypass damper will be required to bypass some of the discharge air back into the return.  These bypass dampers can be used on systems with static pressure ratings up to 0.75” W.C.


The bypass damper should be installed in such a way as to connect the supply air duct to the return air duct.  The damper should be installed in the horizontal position.  Tap into the return air duct at least two feet back from the return air plenum if possible.


With the HVAC unit running, adjust the weight located on the rod so that the bypass damper is fully closed when all zone dampers are in the full open position.  To increase the system static pressure move the weight outward toward the end of the rod.  To decrease the system pressure move the weight inward toward the damper shaft.  To insure that all zone dampers are in the open position while adjusting the bypass damper, disconnect one of the two wires to each of the spring return open damper motors.  Additional weights can be added to bypass damper arm if necessary.

When attaching the weight and arm to a horizontal barometric bypass damper, adjust the damper arm to the 4 o’clock position when air flow is moving left to right.  Adjust the damper arm to the 8 o’clock position when air flow is moving right to left.

Make a call for heating, cooling, of fan in every zone.  Verify that all zone dampers are in the open position. Verify that the barometric bypass damper is in the closed position.  Slowly move the weight upwards on the arm until the damper starts to open slightly.  Then move the weight back down the arm until the damper stays closed. Close one zone and the barometric damper should open.



Updated: March 24, 2008 — 2:49 pm

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