<P> A thermostat is a component which senses the temperature of a system so that the system's temperature is maintained near a desired setpoint . </P> <P> Thermostats are used in any device or system that heats or cools to a setpoint temperature, examples include building heating, central heating, air conditioners, HVAC systems, water heaters, as well as kitchen equipment including ovens and refrigerators and medical and scientific incubators . In scientific literature, these devices are often broadly classified as thermostatically controlled loads (TCLs). Thermostatically controlled loads comprise roughly 50% of the overall electricity demand in the United States . </P> <P> A thermostat operates as a "closed loop" control device, as it seeks to reduce the error between the desired and measured temperatures . Sometimes a thermostat combines both the sensing and control action elements of a controlled system, such as in an automotive thermostat . </P> <P> The word thermostat is derived from the Greek words θερμός thermos, "hot" and στατός statos, "standing, stationary". </P>

How does an electric iron regulate its temperature