Hot water supply, i.e., warm drinking water, is now almost standard in every household. It can be produced in gas boilers, instantaneous water heaters, or with the aid of solar thermal collectors. Central drinking water heaters – storage or flow-through systems must be designed, built, and operated in such a way that the hot water temperature at the outlet of the drinking water heater is equal to or greater than 60 °C. This is necessary primarily for hygienic reasons in order to reliably prevent the formation of Legionella bacteria. This temperature is often too high for heat pumps in residential areas, so electric direct heating is used.