Heat pumps move heat from one place to another. They work similar to refrigeration. The movement of heat takes energy, either electrical energy as in the use of vapor compression heat pumps or thermal energy as in the use of absorption heat pumps. The heat pump efficiency depends on the energy used in moving the heat and the amount of heat recovered from the heat source. Heat pumps are used to provide space heating and cooling, water heating and in some cases recover heat from exhaust air.