A line of PVC and CPVC duct dampers offered in butterfly, gravity, and blast gate types for fume removal applications is available. The backdraft dampers come in three flow control types: butterfly ...

Greenheck’s EM-30 Backdraft Damper series was recently AMCA Licensed for Air Leakage and Air Performance. Designed to open by air pressure differential and close by gravity, backdraft dampers can be ...

They're relatively inexpensive, 15-30 dollars or so, but should be mounted so they can be easily serviced. Dryer backdraft dampers come in several different configurations.