Water heaters

Water heaters are appliances to provide water at the temperature that a person decides. Domestic hot water can be used for many purposes, for example cleaning and cooking. The production of hot water makes up an important share of the overall energy consumption for heating purposes (between 10 and 20%) and this share increases in well-insulated buildings.

One purpose, many technologies

The choice of a water heater depends on the type of building and on the needs of those who will be using it. For example, some water heaters are fit for one tap only, while others can provide hot water to a whole building.

The first differentiation is between on-demand and storage water heaters.


On-demand water heaters, also known as tank-less water heaters, heat water instantly - as it flows through them.

Small tank-less water heaters can be located right where the water is used and are connected with a specific tap. Larger tank-less water heaters are common in centralised systems, such as single flats or one- or two-family houses. Most of these water heaters run on gas or electricity.

Other heating appliances, called combination heaters, are able to both provide domestic hot water and also heat rooms.

Storage water heaters offer instantaneous delivery of hot water and provide great comfort in cases of simultaneous use, for example when two showers are running at the same time.

They can heat water directly, therefore combine in the same appliance a hot water storage tank [link to tech page] and a heating element. The heating element can be a gas or oil burner, an electric resistance heater or an air source heat pump.

In other cases, tanks are heated indirectly. This means that they are connected to an external heater, for example a heat pump, a boiler or solar collectors - or combinations of those.


  • Variety of technologies to meet hot water demand in all buildings;
  • Great comfort for users;
  • With solar thermal water heating, energy from the sun may cover 70% of domestic hot water needs;
  • Heat pump water heaters can reduce energy consumption by 80% compared to traditional water heaters.