Tankless heaters can supply an endless supply of hot water and can save energy. They are an excellent backup for a solar water heater.
Storage tank-type water heaters raise and maintain the water temperature to the temperature setting on the tank. Even if no hot water is drawn from the tank the heater will operate periodically to maintain the water temperature. These standby losses represent 10% to 20% of a household’s annual water heating costs.
Unlike conventional storage tank water heaters, tankless water heaters heat water only as it is used, or on demand. A tankless hot water heater has a heating device that is activated by the flow of water when a hot water valve is opened. Once activated, the heater delivers a constant supply of hot water.