Instantaneous water heaters: tests, saving tips & differences between hydraulic, electronic and fully electronic

Instantaneous water heater in the test

Instantaneous water heaters: tests, saving tips & differences between hydraulic, electronic and fully electronic: instantaneous

Hot tap water is a matter of course in Germany. However, there are several ways to get to the warm water. Instantaneous water heaters - also called hot water geyser, spa or gas boiler - have a little reputation for being big power guzzlers.

But with the right model and the right handling, you can even save a lot of electricity - especially in comparison to a boiler.

If a water heater is operated hydraulically, then it is always dependent on the water pressure, which is why it always requires a minimum flow rate for switching on. In most cases, such a spa has only two possible heating levels. If, during operation, the amount of water flowing through the spa changes, the temperature also changes. So it can happen that the water gets hot or cold during the shower when someone else in the apartment washes his hands at the same time. Hot water geysers of this type are cheaper than electronic ones, almost all manufacturers such as Stiebel-Eltron, Siemens and AEG still have them on offer.

How a water heater works

Instantaneous water heaters: tests, saving tips & differences between hydraulic, electronic and fully electronic: saving

Instantaneous water heater and its mode of operation (Source:

A water heater only heats the water when it is needed. Therein lies the difference to a boiler. Because boilers and water heaters heat the water permanently and thereby drive up electricity costs. However, spas have a smaller capacity than boilers and, in contrast to wall mounted kettles, are not suitable for preparing boiling water. They are mainly used in the kitchen and bathroom. Hot water geysers have different kW outputs (kilowatts). Usual are 18, 21, 24, 27 and 33 kW. The smaller versions are also referred to as small flow heaters and are useful where it depends on a small size.

The device works as follows: Inside is a tube system that can be heated. As a result, the water flowing through can be heated up within seconds. There are also models that are not powered by electricity, but by gas. However, gas heaters are not as compact as the electric ones and have a longer starting time. This shortcoming can be compensated by an integrated small memory. With a higher heat output, more water can be heated at once.

Hydraulically controlled spas

Electronically controlled hot water geyser

If the spa is controlled electronically, it is independent of the water pressure. The amount of water therefore has no influence on the temperature, which means there are no temperature fluctuations with simultaneous operation of several faucets. Although electronic instantaneous water heaters are more expensive than the hydraulic ones, this money is recouped while saving energy costs.

Fully electronic instantaneous water heater

Thanks to the intelligent, fully electronic control, this water heater always keeps exactly the desired temperature and at the same time saves up to 30% of water and energy compared to hydraulic instantaneous water heaters. All pressure and temperature fluctuations are actively compensated.

Installation and maintenance of the spa

You should never install a water heater yourself! It may only be installed by qualified personnel and, in some cases, even requires the approval of the respective energy supply company, which depends in particular on the respective electricity network and that thermal baths require a great deal of energy.

Do you have a water heater that is operated electronically, this usually requires no maintenance. If the spa is operated with gas, the combustion chambers should be cleaned annually.

Advantages and disadvantages of water heaters

The instant water heater does not require the water to travel long distances and the power will be automatically turned off when the tap is turned on. For boilers e.g. a certain amount of water is permanently heated and boilers need a long time after switching off (for example, because you are traveling for a long time) until they have brought the water back up to temperature. With a spa, however, you have warm water immediately.

However, it may happen that the water heater can not be installed because there is no gas connection, or the amperage number of the power line is insufficient. For an electrical connection, the power cross section is decisive. Because electric baths require at least 20 amps. Here is the advantage of gas boiler: Although the efficiency is lower than an electric instantaneous water heater, but only half as much energy is consumed.

Saving tips for instantaneous water heaters

You should be able to set the heater to specific temperatures, as this can save a lot of energy. Similarly, good insulation of the hot water pipe reduces energy consumption. In addition, you should never mix in cold water, because it consumes only unnecessary energy.

The temperature should be kept below 60° as much as possible, because this reduces the limescale deposits on the heating elements, and limescale deposits cause higher power consumption. It is also important to avoid long distances, so the heater should be placed near the tap or shower to prevent heat loss. If the pool and shower are far apart, you should think about purchasing a small separate heater for the sink.

A shower column in combination with a water heater

Anyone who runs a spa and would like to purchase a shower column with several massage jets, should urgently make sure that this also works with the water heater. It can happen that the shower columns consume more warm water than the spa can produce. In most cases, the possibility of using with water heater is noted in the product description.

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