Refrigerant circulating in the heat pump detracts the heat from the air, water or ground, changing its state from liquid to gaseous and evaporating. Stage Two - Compression: The heat pump’s compressor compresses the several-degrees-heated gas refrigerant rapidly and multiplies the small heat gain using the physical principle (the higher pressure the higher temperature) to a higher temperature level, about 80°C. Stage Three - Condensation: The heated refrigerant transmits its heat to the water in the heating or hot water circuit in the second exchanger, in doing so it then it cools down and condensates. The heating or hot water system then emits the gained heat and the water in the system then goes back to the exchanger to be heated again. Stage Four - Expansion: The refrigerant goes back to the first exchanger through the expansion valve which regulates the flow of refrigerant which then is heated up again in the evaporator. This cycle repeats constantly.