Controls, controllers or switches come in many forms for specific needs of the equipment it is controlling. There are speed controls including 2 speed, 3 speed or variable speed controls. Thermostats with varying temperature ranges. Thermostats with probes for reading temperatures in duct work. 2 stage thermostats for 2 speed heating or cooling. Carbon monoxide detector sensors that can activate ventilation when necessary. Industrial Fans Direct carries a wide variety of controls and switches.