Dampers typically control the flow of air into, throughout and out of the furnace system. The types of dampers required vary by furnace design, but most consist of piping and valves.
Chimney dampers are commonly used with furnaces and prevent cold air from entering the building when the furnace is not in use. These dampers also allow gases generated by pilot lights to vent out of the home. Furnace systems that draw air from outdoors often use backdraft dampers, which often use a butterfly valve that pulls in air when the system is in use and automatically close when the system turns off. As of 2015, modern condensing furnaces sometimes use the same piping for intake and exhaust, leading to integrated fixtures that contain multiple dampers.