In a home, a thermostat is the HVAC control that manages the operation of the furnace or air conditioner, and the blower that distributes heated or cooled air. In the past, thermostats were basic devices that simply started the equipment at a certain temperature set point, and then shut it off at another.

HVAC (Heating, Ventilation and Air Conditioning) equipment needs a control system to regulate the operation of a heating and/or air conditioning system. Usually a sensing device is used to compare the actual state (e.g. temperature) with a target state.