The thermostat works by switching heating or cooling devices on or off. This is what happens in a central heating system or an air conditioner. In some systems it works by switching a 'heat transfer fluid' off or on as needed to keep the set temperature. The name is derived from the Greek words thermos "hot" and statos "a standing".
Because they control a system, thermostats are examples of feedback devices which maintain a steady local environment against temperature changes outside the outside world. In cybernetics, the thermostat is an example of a machine which uses feedback to maintain the stability of a heating system.
- Ashby, W. Ross 1960. Design for a brain: the origin of adaptive behaviour. 2nd ed, Chapman & Hall, p44.