Which system, referred to as an "on-demand" system, provides heated water only when needed?

A tankless water heater, often referred to as an "on-demand" system, provides heated water only when it is needed. Unlike traditional water heaters, which continuously heat and store a certain amount of water in a tank, tankless systems heat water directly as it flows through the unit. This means that there is no standby energy loss from keeping a reservoir of water heated.

When a hot water tap is turned on, cold water travels through a pipe into the unit, where either a gas burner or an electric element heats the water. This on-demand feature allows for an unlimited supply of hot water, making it efficient and convenient for households. As a result, tankless water heaters can save energy and reduce costs because they eliminate the energy wasted in maintaining the temperature of stored water.

In contrast, standard water heaters, heat pumps, and storage water heaters involve some form of heating or storage of water before use, leading to energy loss due to standby heating. Therefore, the tankless water heater stands out in its ability to provide hot water instantly and only as needed.