Table of Contents

Selection Criteria Electric Water Heaters


Topten (Best products of Europe) lists the most energy efficient electric water heaters with storage. The listed products function with air source heat pump and are limited to consolidated, factory made systems. They must deliver a minimal coefficient of performance (COP) according to EN 16147 or EN 255-3. The coefficient of performance describes the ratio of heat in tapped warm water to consumption of electricity. As an alternative system, solar water heating systems are presented on some country-Topten-sites.


There are many different systems to supply domestic hot water (combined with space-heating, separate with a storage tank or separate and tankless by heating the water instantaneously). The energy used varies from oil or gas boilers, to electrical resistance heaters or (electrical) air source heat pumps, to renewable sources like solar collectors, wood or industrial waste heat (often combined with space-heating as backup in winter and with electrical heaters in summer).

Domestic water heaters with air source heat pumps use much less electric energy than electrical resistance heaters, because they use electric heat pumps to extract heat from the surrounding air or from outside. Of course, the air source must not be from a heated room, since this would steal energy from the heating system. In Europe, every third domestic water heater is an electrical resistance heater. Around 4 million units electric water heaters with storage (>30 l) are sold per year (estimate from European Commission Joint Research Center for 2007).

The most sustainable way of supplying domestic hot water is by using renewable energy, of course. For some countries, solar water heating systems are presented on their Topten-site.

Technical criteria

Coefficient of performance (COP) according to one of the following european standards:

  • EN 255-3: 1997 (in July 2011 substituted by EN 16147: 2011):
    • COP higher than 3.0 for heat source temperature of 15°C
    • COP higher than 3.5 for heat source temperature of 20°C
  • EN 16147: 2011: COP higher than 2.3

Measurements according to EN 255-3: 1997 will be accepted until further notice.

Data Sources

  • National data-bases and Topten-sites such as
  • All data is given by the manufacturers.
  • The coefficient of performance (COP) must be proven by a test report pertaining to one of the two demanded standards.

Order of presentation

The products are ranked by brand names. The order of presentation can be changed by clicking on the headings of the tables.


Control type for electric heating

One-time buttons (they trigger the water to be heated up higher once) or timer clocks (for example only Saturday night) help avoid that the electric heating stays on unintentionally. A simple switch should at least be illuminated or combined with an indicator lamp, in order not to be forgotten left on.

Max. temperature without electric heating

Highest adjustable water temperature when operating only with the heat pump. With the electric heating or an additional heat exchanger the temperatures rise higher.

Electric heating

Allows the water to heat up at about twice the speed and to higher temeratures than by operating with the heat pump only. The temperature is normally set to 65° C.

Additional heat exchanger

Here, the boiler can be connected for fast heating and for covering peaks in warm water demand. Another option is to connect solar collectors.

Air ducts

Air ducts allow to supply (and conduct) the air from outside or the next room. The supplied air serves as heat source and cools down in the process.

Available in countries

This item displays the availability of models in European countries according to producers’ information. "EU" means all countries of the European Union. "On demand" means, that producers could not indicate the availability and that consumers have to ask in their countries on their own. The country codes are according to ISO.


Standards and Labels


Producer and retailers are kindly asked to contact info(at) to inform about more products which meet the Topten selection criteria.


03/2012 Nipkow/Geilinger