The AeroTherm utilizes both heat-pump technology and back-up electric heating elements to heat water. This integrated system helps to drive the AeroTherm's economical and efficient operation. During heat pump operation' a fan draws heat from the air into a compressor and evaporator to heat refrigerant. Once heated' the refrigerant travels through a coil that fully surrounds the water storage tank. Heat is directly transferred to the water in the tank.