They are set up inside the HVAC ductwork and therefore are brought on to close once they perception smoke. Smoke dampers are often made from aluminum and have a motorized actuator that closes the damper. Backdraft dampers are either gravity or motorized. Gravity backdraft dampers utilize the power of gravity https://air-control-dampers-for-h47789.blogolize.com/5-tips-about-air-control-dampers-for-engine-sheds-you-can-use-today-75567421