Electric immersion heaters are used to prepare domestic hot water. Immersion heater fulfils its task if, for example, the heat pump in winter can not deliver the right amount of heat. In a hot water storage tank, an electric immersion heater is useful in the summer, when the central heating is not used or when the produced by the solar panels hot water on cold days is insufficient. Despite cheaper ways of obtaining heat, an electric immersion heater is still a popular reserve method of heating water for utility purposes in homes or offices.