PTF & PTDD series Inline Duct Fans are well suited for indoor exhaust fresh air systems, ventilation, and humidification. Each fan includes smart wired technology that can detect the environmental temperature and adjust the motor speed from Low, Medium, and High. It also includes a room temperature display and a timer setting that can be set from 1-30 minutes. Service life is enhanced by a relay switch that has been tested for greater than 100,000 times.