Instant water heaters, or tankless water heaters, are electrical devices used to provide domestic hot water for residential or commercial spaces. Their operation is based on a heating element that heats water in real time, for as long as the tap remains open—meaning hot water does not run out, unlike a conventional water heater or solar water heater. Instant water heaters provide water at a constant temperature, and the higher their power, the faster they heat the water to offer a greater flow at the selected temperature. Newer models feature a heat exchanger with heating elements that do not accumulate scale, which is why they offer a multi-year warranty for proper operation. They do not have a storage tank like solar or conventional water heaters, and therefore do not store hot water that may ultimately go unused. Furthermore, they are self-regulating (digital – inverter), meaning they automatically adjust their power to meet our needs with the lowest possible energy cost. They can be installed in series with other hot water supply units (e.g., solar water heater, heat pump, boiler, etc.) and operate only when the temperature of the water they receive from the other unit is lower than desired, thus providing hot water at the desired temperature instantly and economically in terms of energy and water consumption.