The warm exhaust gases are then vented up a flue pipe through the roof. This robs a building of heated air. An automatic vent damper not only restricts the flow of heated air up the chimney, but can also reduce the amount of cold outside air leaking in to replace the escaping warm air. It is placed in the flue pipe between the heating unit and the chimney to block the passage of heat after the unit has been shut down. The time needed to reach this point is reduced as a result of the vent damper.
Vent dampers can also help to retain humidity in the building by reducing infiltration.
This can improve comfort in the winter months. The electromechanical vent damper is coupled with the gas valve. It opens when the thermostat signals that the heating unit is on and closes when the thermostat signals the unit is off. These have fail-safe mechanisms to prevent them from locking in the closed position. A thermomechanical damper, unlike its counterpart, has no electrically activated parts.