Vents KOM 125 U 5 inch Backdraft Damper buy2get20 They also have a relay

They also have a relay output that can turn your fan on or off based on indoor CO2 levels

and other public and commercial spaces

this garage exhaust fan kit mounts cleanly through the wall using the included PVC sleeve and exterior grille

and applications where a standard inline duct fan may not provide enough power

As a Ductless Energy Recovery Ventilator

Vents KOM 125 U 5 inch Backdraft Damper buy2get20 They also have a relayThe Vents KOM 125 U Spring Loaded Backdraft Damper is made for 5" round duct systems. It prevents backdraft, insects, and birds when the ventilation system is off. Its operation is simple: blades open with airflow and close securely due to a strong spring. This KOM 125 U damper is easy to install in 5" round ducts, and features a 26 gauge galvanized steel housing and precision engineered aluminum blades with spring action. It also has foamed rubber