They are really put in during the HVAC ductwork and so are brought on to shut whenever they sense smoke. Smoke dampers usually are made from aluminum and also have a motorized actuator that closes the damper. Backdraft dampers are either gravity or motorized. Gravity backdraft dampers use the drive https://aircontroldampersforhotcl89011.blogthisbiz.com/43665190/new-step-by-step-map-for-air-control-dampers-for-hot-climates