They use sources such as air, water, soil, and waste heat, and are classified based on the type of source as air-source, water-source, or ground-source heat pumps. Depending on the heat transfer medium, they can be air-to-air, air-to-water, water-to-water, or water-to-air systems. There are many different types and applications available, making them environmentally friendly products due to their use of renewable energy sources and reduction of dependency on fossil fuels.

Heat pumps consist of a compressor, expansion valve, condenser, and evaporator, forming a refrigerant gas circuit. The efficiency of heat pumps depends on the difference between the fluid temperatures produced by the heat source used and the coefficient of performance of the device. The smaller this difference, the higher the efficiency.

The main principle in heat pumps is to maintain the temperature of the source as balanced as possible and close to the selected heating-cooling system's temperature regimes. Therefore, low-temperature heating and high-temperature cooling systems should be preferred in heat pumps.