Over sink water heaters typically come in two varieties: storage water heaters, with various litre capacities and tankless water heaters. Storage water heaters store and repeatedly heat water within a tank, while tankless water heaters instantly heat the water as it flows through the device, and do not retain any water internally except for what is in the heat exchanger coil. They are typically used to provide hot water for sink taps and shower heads.
With traditional storage water heaters, once the water stored inside the tank has been heated, it may be streamed until it is depleted, at which point the new supply of water must be heated. With these heating devices, over sink water heaters tend to have a smaller tank than a typical boiler.
Tankless water heaters are typically installed near their point of use. Unlike storage water heaters, these devices offer a plentiful continuous flow of hot water and potential energy savings thanks to their greater efficiency.
Certain models of over sink water heaters are intended to be installed in specific locations, such as under a sink. Many, but not all, feature a component for temperature control such as a knob. They are available to buy with different litre capacities depending upon your requirements.
All water heaters that burn gas need to be adequately vented.