This MFD Mechanical Fireplace Damper prevents heat from escaping up through the chimney when the fireplace is not in use, and prevents backdraft down the chimney. It is designed for chimney top installations.
The MFD is used as a component in a combined fan and damper system. The damper actuator can be interlocked to a control (ADC100 or ADC150) so it only operates when the fireplace is in use and the fan is running.