The Fantech Makeup Air System is a "powered" or "fan-forced" system. The Makeup Air System is triggered when the compensated exhaust system is energized. The Makeup Air System damper opens and the Makeup Air System fan is powered on. The fan is speed-controlled relative to the speed of the compensated exhaust system's fan speed. In otherwords, as you speed up the exhaust fan, the Makeup Air System fan speeds up too, and vice versa.