We recommend Backdraft Dampers as the next line of defense against odor control. Backdraft Dampers prevent air from reverse flowing through the fan when powered off.
Ours are available in 6 different sizes from 4" - 14" and are spring loaded for positive closure. The rigid design is constructed from galvanized steel for the collar and lightweight aluminum for the damper blades.
They can be mounted horizontally or vertically for horizontal or vertical airflow.