Automatically slows down or speeds up centrifugal fans to respect user selected temperature day and night setpoints. Enables a much tighter and precise temperature curve. When ON/OFF controls usually yields a variation over 5F/3C, TV1 will yield a variation below 2F/1C. 6 foot cord with temperature sensor precise to 2F/1C. Can drive single phase 120 Vac induction motor type fans up to 750 Watts. Any forced ventilation rooms should be equipped with this type of control to promote faster and more vigorous growth. 3 year warranty.