Thermostats control nearly all types of heating and cooling equipment, keeping room temperatures within a set range. By doing so, they ensure comfort, cut energy waste, and offer considerable convenience.

A thermostat has a temperature sensor and an activating switch. Some are mechanical, others electronic. Not all thermostats work with all types of furnaces and heaters; a forced-air thermostat, for example, won't necessarily work with a heat pump. Most thermostats are either manual, electronic or "line-voltage" (used with electric baseboard and wall mounted heating).

Programmable, electronic thermostats couple sensors with circuitry to do the job. Typical programmable thermostats can handle both heat-only systems-such as forced-air, steam, hot water, and, in some cases electric-and complete air-conditioning systems. Most are like minicomputers that can automatically align heating and cooling to changing daily needs, eliminating unnecessary energy usage and reducing energy costs.