"Heat pumps are considered energy efficient alternatives to furnaces and air conditioners. As the heat pumps remove heat from one space to the other, the cost of operating them are lesser than that of conventional heating and cooling appliances. Generally, there are three different kinds of heat pumps. They are the air source heat pumps, the water source heat pumps and the ground source heat pumps. These heat pumps collect heat from air, water or ground outside the house and it is used inside later on. However, the commonest among these is the air source heat pump. The air source heat pumps transfer heat between the house and the outside air. The efficiency of heat pumps is so high that it reduces around 50% usage of electricity. On the other hand, the water source heat pumps use water to absorb as well as dissipate heat. Last but not the least, ground source heat pumps transfer heat between the house and the ground. They have a lower operating cost because they take heat from a more constant source of heat that is the ground."