water heater

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Simple modern kettle without a base and without temperature control with a stainless steel vessel for 0.5 l

Kettles are electrical kitchen appliances that can be used to heat water particularly quickly. Since the heating element is integrated in the device, neither a stove nor an open fire are necessary. Depending on the model, there are kettle, jug or jug-shaped designs of the cooking vessel. Many devices work with a heating coil housed in a metal tube based on the immersion heater principle . Cleaning is easier with devices in which the heating element is under a base plate. With many kettles, the cooking vessel can be removed from its contact base and thus easily disconnected from the circuit and moved freely.


Electric kettle, designed by Peter Behrens , 1909

Electric kettles have largely replaced the whistling kettles and immersion heaters that were previously used to heat water .

The first electric kettle was shown at the Chicago World's Fair in 1893 . Long before that there were (non-electric) table stoves for people without access to a stove.

Layout and function

Modern kettles usually consist of two parts:

  • a removable cooking vessel made of plastic , metal (mostly stainless steel ) or glass with heating element (mostly covered, heating a base plate made of stainless steel)
  • as well as a separate contact foot with supply cable, which provides the power supply for the cooking vessel placed on the base via a plug connection .

Such two-part devices are often referred to as “wireless” in trade and advertising, which means that the detachable cooking vessel is not connected to the power supply with a cable, but is connected to the power supply by placing it on the contact base Taking off is disconnected from the electricity.

In addition, one-piece devices are offered, which are usually also equipped with a concealed heating element. With these devices, the connection cable should be disconnected from the mains before filling with water in order to reduce the risk of an electrical accident .

The cooking vessel usually has a (plastic) lid as protection against splashing and scalding in order to reduce evaporation and to keep the heat in the container. An automatic switch-off when the boiling point is reached is only functional when the lid is closed. Some devices have a spout with a permanent water filter.

For filling with water, the lid can usually be folded up manually at the push of a button or it can be removed completely. With some devices, filling is also possible and provided directly via the spout. The prerequisite for this is a correspondingly wide spout and a permanent filter that enables water to flow in both directions (e.g. by automatically folding away due to the water pressure / gravity), or the general waiver of a corresponding filter in front of the spout.


Inside view of a kettle with the round bimetal element that can be seen on the left, which switches off with steam

Kettle having a heating element in addition to the snap-action switch ( temperature switch ) connected to a bimetal , the device off automatically. Together with an on / off switch mechanically coupled to it, it is arranged in the housing of the cooking vessel in such a way that it is not heated by the water, but only by the steam produced, which is only created in large quantities when it is boiling and therefore only switches the temperature switch off . For the shutdown to function correctly, the cover must therefore be closed, otherwise the resulting steam will escape and not reach the temperature switch. Some types of device switch off when the cover is opened.

In many devices, the electrical connection to the mounting plate is in the form of a concentric plug connection. This usually contains a feeler pin that switches off the device when it is lifted, provided that the automatic switch-off has not yet responded. As a result, in this case too, the device switches off before the electrical plug connection between the device and the base is mechanically interrupted. This prevents the plug connection from being damaged or worn by tear-off sparks . Above all, this also prevents a device that is accidentally still switched on from being returned to the base and unintentionally continuing to heat.

The kettles used today have a temperature fuse that works independently of the automatic switch-off ( dry boil protection ). This often also works on the shutdown device and is then reversible. However, kettles should not be left unattended or left empty.

In the device base or the cable plug of the connection cable there are sometimes additional, irreversibly triggered thermal fuses against overheating.


A distinction is made between kettles with concealed and exposed stainless steel heating elements. T. no longer in the form of conventional heating wires, but designed as printed circuits .

Exposed heating element
The heating coil enables a compact device design. Since it has to be completely covered by water, small amounts of water cannot be heated without risk.
Concealed heating element (stainless steel heating floor)
Easily accessible, but with a smaller heat transfer surface, and therefore a stronger boiling noise - some devices therefore optionally offer a special operating mode for a slower but particularly quiet heating process.

Performance and efficiency

Common household kettles have a capacity of one to two liters (electric kettles for the commercial sector also up to four liters) and a heating power of 600 to 3100 watts . A higher power consumption goes hand in hand with correspondingly shorter cooking times and less heat transport into the environment, so high-performance devices have a slight advantage over slower kettles in terms of energy balance.

Some can-shaped devices with an encapsulated heating base have special filling devices, double reservoirs or more precisely resolving fill level indicators in order to be able to fill very small amounts of water (e.g. a cup and less) precisely and heat it up in a targeted manner, in order to be able to use energy, water and time to save.

Kettles heat water as efficiently as immersion heaters , and modern models also switch off automatically and are therefore more economical and safer than immersion heaters.

Immersion heaters and kettles heat water more efficiently than electric hotplates. This is because the energy is transferred practically directly to the water and does not have to heat the stove top and its surroundings.

In Germany, heating water with a kettle was more expensive in 2006 (approx. 1.9 cents per liter) than on a gas stove (approx. 1.5 cents per liter).

For 2019 in Germany, the gas stove will cost 1.59 ct per liter (gas price: 6.34 ct. Per kWh, efficiency: 38%) and the kettle 3.3 ct. per liter (average household electricity price: 30.85 cents per kWh, efficiency: 89%). Even with efficiency levels of 30 to 40% for gas stoves, gas always has a price advantage.

For comparison, the efficiency of a ceramic hob for heating 1 liter of water by 80 Kelvin is 56%.

Health aspects and safety

Most kettles are harmless from a health point of view. However, some specimens can release nickel or hormonally active substances ( bisphenol A ) into the water, especially if the water remains in the device for a long time. This applies in particular to devices with an exposed heating coil or those with a plastic housing.

Microplastics can dissolve from plastic kettles into the boiling water. In a random test, this was the case with all four devices tested, each in different concentrations. Possible effects on the user when drinking or otherwise consuming are still unclear. In 2019, the Swiss consumer magazine Saldo tested ten plastic kettles. In six of the tested kettles, plastic particles between 5 and 50 micrometers in size dissolved during cooking.

Kettle with temperature setting

In addition to the pure cooking function, some devices also offer the option of heating the water to a selectable temperature - for example between 40 ° C and 100 ° C (e.g. for preparing tea at 90 ° C and other hot drinks) and, if necessary Maintain temperature over a longer period of time. For the preparation of baby food, some kettles also have an automatic boiling function, which first heats the water to the boiling point and then keeps it at a preset lower temperature for a longer time after it has cooled down again.

In particular, devices with a metal vessel pose a risk of burns if the z. T. over 90 ° C heated surface is accidentally touched while handling. Devices with a glass or plastic surface, as well as devices with an insulating double jacket, offer better thermal insulation properties. A scald with boiling water can cause second-degree burns to large areas. Accidents happen when children have access to kettles, especially when pulling on the hanging power cord is dangerous.

Kettles have a specified maximum capacity to avoid boiling over. The lid must be closed when heating, otherwise the shutdown will not work. Instructions for use warn against submerging the kettle in water as the electrical system is not encapsulated in a watertight manner.

Other designs

Boiling water device

Permanently installed, pressureless boiling water device (5 l)

Another design are so-called boiling water devices (boilers) . These are permanently installed containers with a capacity of around 5 liters, which are able to heat the water up to the boiling point (but also adjustable lower temperatures). The device is usually installed directly above the sink and connected to the water pipe. This is mainly found in old buildings, as the simple cold water taps on the wall above the sink that used to be common can easily be replaced by a boiling water device.

When using the device, the required amount of water (can be checked by means of a filling scale on the front of the container) from the water pipe is first let into the vessel through a tap, then the device is switched on. After a few minutes the water will have reached the desired temperature. This is usually indicated by a control lamp going out, but sometimes also by an acoustic signal. The water can be drained into a container or the sink using the drain tap. A third valve enables cold water to be drawn from the line bypassing the device at any time or to be added to the hot water when draining. The valves are usually located as a separate fitting below the container, but there is also a design in which they are integrated into the housing, which reduces the overall height and the device can be more easily installed in a fitted kitchen below wall cabinets. In this variant, there is sometimes an additional valve that can be used as a device connection, e.g. B. for a dishwasher is intended. The water tank of a boiling water device usually has a small opening at the top through which the descaler can be poured in to clean scale . In older devices, the container is often made of glass; today, accordingly, heat-resistant plastic is common, and the containers are now also provided with thermal insulation and cladding that reduces energy consumption and protects against burns on the hot surface.

Boiling water devices are more expensive and not as flexible to use as mobile kettles because of their fixed installation, but they may pose a lower risk of accidents for children because they cannot be torn off or overturned. In view of the central hot water supply that is common today, they are rarely installed.

Hot water dispenser

Two hot water dispensers

With hot water dispensers, the required amount of water is pumped out of a water tank at the push of a button and heated to the set water temperature. A distinction can be made between two modes of operation for hot water dispensers. The water is either heated by a flow heater and poured out immediately or first pumped into an integrated kettle, heated there to the required temperature and then poured out.

Electric jug

Japanese kettle

A special type of kettle that is almost unknown in Europe is the "electric jug" (電 気 ポ ッ トdenki potto ) from Japan . This is a kettle that constantly keeps water heated to a predetermined temperature ready. The heating output of such models is usually lower than that of European models, but it requires a holding power of approx. 50 watts . These devices do not have to be lifted for pouring, as a pump conveys the hot water through the outlet at the push of a button.

Electric samovars , which are common in Russia and Turkey, work in a similar way . Instead, they have a tap for drawing off water.

See also

Web links

Commons : Electric kettle  - collection of images
Wiktionary: kettle  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. Stiftung Warentest: test 01/2013 Kettle ( online version ): "Nothing heats water faster than an electric cooker - neither microwave, glass ceramic hob, hot plate or gas stove are faster."
  2. Stiftung Warentest: Kettle - Many bad grades. In: test 08/2006 (article can be downloaded as PDF; accessed: February 4, 2013)
  3. https://www.bundesnetzagentur.de/DE/Sachgebiete/ElektrizitaetundGas/Verbrauch/PreisRechnTarife/preiseundRechnungen-node.html Bundesnetzagentur : prices f. Electric power and gas, accessed on May 25, 2020
  4. a b c https://download.test.de/filestore/t200608064.pdf?path=/protected/94/38/c42b3070-1046-43a3-85ea-c00087e2e7c4-protectedfile.pdf&key=BBF5D4ADCCE37A3C6C8F2FC4C97719E1FB616791 Foundation goods test journal test , Issue 8/2006, page 64 ff, accessed on May 25, 2020
  5. http://www.haus-wissenswertes.de/einrichtungen/kueche/gas-oder-elektroherd.html gas or electric stove, accessed on May 25, 2020
  6. ^ Foundation Ökotest Kettle short version (2008) ( Memento from December 3, 2013 in the Internet Archive )
  7. NDR: Kettle: Danger from microplastics? ( ndr.de [accessed on September 14, 2018]).
  8. Raphael Knecht: Microplastic ends up in the tea in these kettles . ( 20min.ch [accessed on November 22, 2019]).
  9. Schmirkee: German: Model of a kettle where the temperature can be adjusted. Provided by https://wasserkocher-mit- Temperatureinrichtung.com. August 29, 2017. Retrieved October 17, 2017 .
  10. https://www.kindersicherheit.de/produktsicherheit/datenbank/az/wasserkocher.html Message from the Federal Working Group on More Safety for Children e. V. on kettles, accessed on May 25, 2020
  11. https://api.meleven.de/out/kodi/4e.bf.2f.1225600612256105manualddb76b4a.pdf instructions
  12. Press release of the Federal Association for More Security for Children e. V .: Attention kettle: Babies are particularly at risk ( Memento from October 20, 2008 in the Internet Archive )