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 5?F/3?C, TV1 will yield a variation below 2?F/1?C. 6 foot cord with temperature sensor precise to 2?F/1?C. Can drive single phase 120 V 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.