Air source heat pump takes advantage of a little electric power to make the compressor work, put high-pressure working medium to expansion tank for expansion and to evaporator to make it gaseous. In this process the medium absorbs a lot of heat from the air, then the compressor makes it high-pressured and high-heated liquid. this liquid goes through the condenser and transfer the heat to water. In this way water is heated. It can save energy up to 80% compared to traditional gas boiler or electric heaters.