A heat pump moves energy in the form of heat from one point to another. Heat pumps are realized through several physical effects.

The most common are

• gas compression heat pumps
• phase change heat pumps
• thermoelectric heat pumps use the Peltier effect
• geothermal exchange heat pumps

Refrigerators, Air Conditioners and heating system are all common applications of heat pumps.

When comparing the performance of heat pumps, it is best to avoid the word "efficiency", as it has many different meanings. The term coefficient of performance or COP is used to describe the ratio of heat output to electrical power consumption. A typical heat pump has a COP of about three, whereas an electric heater has a COP of just one.