Last updated: 16/10/2022

Welcome to our big water heater test 2022. Here we present all the water heaters we have tested in detail. We have compiled detailed background information and added a summary of customer reviews on the internet.

We would like to make your purchase decision easier and help you find the best water heater for you.

You will also find answers to frequently asked questions in our guide. If available, we also offer interesting test videos. Furthermore, you will also find some important information on this page that you should definitely pay attention to if you want to buy a water heater.


  • The hot water boiler should be sized to supply the sufficient amount of water. Devices that are too large should be avoided, as this increases operating costs and also requires more space.
  • The main distinguishing criterion for water heaters is their size. In general, water heaters can be divided into small units and medium to large units, which differ in their capacity and mode of operation.
  • Small units offer high flexibility in terms of installation and space requirements. The energy costs and also the purchase costs are lower than for medium and large units.

The Best Hot Water Boiler: Our Choices

Guide: Questions you should ask yourself before buying a water heater

What is a water heater and how does it work?

The term boiler (English: “to boil”) already describes the basic functional principle of a hot water boiler. A water heater is similar to a household water boiler.

To always have hot water, you need a hot water boiler. (

Cold water is fed into the storage tank, which is then heated to the selected temperature and can be withdrawn from the tank as needed.

Most water heaters heat water mainly with electricity. The casing therefore usually contains a metal-jacketed heating element that converts the electric current into thermal energy and heats the surrounding water.

The stored water is heated to about 60° to 80°, rarely even up to 95°C.

The desired temperature is set via a regulator with a temperature-dependent switch and the heating element is switched off when the selected temperature is reached or switched on again when it cools down considerably.

Depending on their size, hot water boilers hold a certain amount of water, which they heat and then keep at the same temperature. The classic boiler is usually filled and heated just before the water is drawn off and therefore does not require thermal insulation. Examples are bath ovens and boiling water appliances.

The amount of hot water that can be drawn off in a short time depends on the storage tank size of the boiler.

The connected load in turn determines the amount of water that can be drawn off permanently. By the way, if you don’t have any windows in the bathroom but still like to enjoy a hot bath, you might want to get a bathroom fan. This product prevents mould from forming in your bathroom.

What should I consider when buying a water heater?

Before buying a water heater, there are some basic questions you should ask yourself. It is particularly important that you consider what is to be heated and to what extent.

You should choose your hot water boiler according to your hot water needs. For a rarely used washbasin in the guest toilet, a small appliance is usually sufficient. (Source: / Ihotsky)

For an infrequently used washbasin in the guest WC, a small appliance may be sufficient. For a bathroom that is used a lot and is available to several people every day, you need a hot water tank with a larger capacity.

But structural and consumption-related aspects should also be taken into account in the planning. For example, if the bathroom is narrow, this makes it difficult to install a large hot water boiler.

In any case, you should have the installation of non-plug-in appliances carried out by the respective manufacturer or a specialist company.

The hot-water boiler should be sized so that it supplies a sufficient amount of water. You should avoid choosing a storage volume that is too large, as this increases operating costs and also requires more space. For a household, 40 litres per person per day is assumed.

What does a hot water boiler cost?

The price range for water heaters is very wide. Depending on the model, capacity, operating mode and manufacturer, the price can be quite different. Small water heaters can already be purchased at a very reasonable price. The larger the capacity, the larger the boiler and the more the appliance costs.

Type Price range
Hot water boiler 50 to 800 €

Hot water boilers can be purchased for as little as €50. Depending on the model, however, the boiler can cost up to €800 if you need a very large storage tank.

What alternatives are there to hot water boilers?

If you don’t want to buy a water heater or are considering an alternative way of supplying hot water, you can use an instantaneous water heater or a pure water storage tank, for example.

We have prepared a clear table with all the alternatives.

Alternative Description
Instantaneous water heater Instantaneous water heaters do not store hot water. This makes these devices very compact. Water is only heated when needed. When the hot water tap is closed, the heating process of the instantaneous water heater also stops.
Pure hot water storage tank Unlike boilers, pure heat storage tanks use energy from external heat sources.
Condensing boiler In a condensing boiler, the heating water is heated via combustion heat. However, the heat contained in the flue gas does not escape unused through the chimney, but is used by the condensing boiler. Condensing boilers are used to supply hot water and for heating.

Alternatively, you can also use an instantaneous water heater, hot water tank or a condensing boiler.

Decision: What types of water heaters are there and which one is right for you?

The main criterion for differentiating between water boilers is their size. In general, water heaters can be divided into small appliances and medium to large appliances. These models differ not only in their capacity, but also in their mode of operation.

Hot water boilers have some advantages but also disadvantages, which we would like to share with you.

  • Simple models available at a reasonable price
  • Constant water temperature of the entire filling quantity
  • No water loss due to “running hot”
  • Limited capacity
  • Hygienic concerns with prolonged standing water
  • Waiting time until first reaching target temperature

Both variants have their own advantages and disadvantages. We will now go into more detail on the exact differences and what needs to be considered. Distinctions are made:

  • Small appliances
  • Medium and large units

What distinguishes a small appliance and what are its advantages and disadvantages?

Small storage tanks with a volume of approx. 5-15 litres come into question in places where small quantities of hot water are often needed but which do not have a 400-volt power connection for an instantaneous water heater.

  • High flexibility in terms of installation and space requirements
  • Lower energy costs
  • Lower purchase costs
  • Operation via simple mains connection
  • Significantly limited capacity
  • Only suitable for low hot water demand

Small, mainly electrically heated hot water boilers are mainly used to supply hot water for sinks and washbasins when a central hot water supply is not available or it is not worthwhile to connect it.

This can be the case if the water tapping point is far away or is rarely or irregularly used and it therefore seems unfavourable for energy reasons or is hygienically problematic in the case of prolonged low temperatures.

These designs are available for both under-sink and wall mounting. Small hot water boilers operate with a connected load of 2,000 watts and can thus usually be operated without any problems via a simple mains connection.

However, there are also small gas-powered devices for motor homes and camping caravans. (Source: / MemoryCatcher)

What distinguishes a medium-sized and large appliance and what are its advantages and disadvantages?

Hot water boilers with a volume of 30 litres or more are suitable for supplying a shower, a bathtub or several taps.

  • Demand of a whole household can be covered
  • supply of several taps
  • flat storage tank available for smaller space requirements
  • Higher purchase costs
  • More demanding in terms of space
  • Higher operating costs

Medium-sized boilers of 30 to 200 litres are often used to supply hot water to a residential unit with average hot water requirements. They are usually found in fully electrified flats and houses. With sufficient dimensioning, heating up once a day is sufficient.

Medium-sized units are designed for wall mounting, as floor-standing units or horizontal storage tanks. For some time now, there have also been flat storage heaters with a shallow depth. The electrical connected load is up to 4,000 watts. This places higher demands on a suitable electricity grid and also produces significantly higher electricity costs.

Rarely used, especially in private households, are even larger storage tanks with more than 200 to several thousand litres.

These models are even suitable for supplying hot water to apartment buildings. They are usually operated with night-time electricity in order to reduce electricity costs as much as possible.

However, models in this size range are also available with gas operation. Alternatively, they are also available with so-called bivalent heating, in which two different types of heating are used. This means that electricity or gas or even a heat pump can be used in parallel.

A large water heater with a storage tank of more than 200 litres is even suitable for supplying an apartment building with hot water. (Source: / Antranias)

Purchase criteria: You can use these factors to compare and evaluate water heaters

In the following, we will show you which aspects you can use to decide between the different models of water heaters.

The criteria you can use to compare water heaters include:

  • With or without hot water tank
  • Over-the-table or under-the-table design
  • Wall-mounted, floor-standing or floor-standing unit
  • Unpressurised or pressurised
  • Energy requirement

Now we will go into more detail about the individual buying criteria.

With or without hot water tank

Hot water boilers are available both with and without a hot water tank. The classic boiler is not a hot water storage tank. An example of this are boiling water appliances. Here, the water is heated just before use. Therefore, these appliances are not insulated against heat loss.

The advantage of hot water boilers without a storage tank is that only the amount of water needed at any one time is heated, thus saving energy. In addition, the water can be heated to boiling point and can therefore also be used to make tea or coffee.

A hot water boiler with storage tank remains completely filled with water throughout. The water storage tank made of copper, stainless steel sheet, plastic or galvanised or enamelled sheet steel is located in a plastic housing. These models are insulated and thus enable the water temperature to be maintained for a long time.

Over-the-table or under-the-table design

Small hot-water boilers are offered as so-called over-the-sink models, i.e. they are mounted on the wall directly above the tapping point, for example a washbasin. They are connected to the cold water pipe, but usually have their own, permanently installed mixer tap.

Hot water boilers with a hot water storage tank are more elaborately designed. Depending on the size, they are either over-the-sink or under-the-sink units. Larger boilers are usually only offered in an above-table version.

Wall-mounted, floor-standing or horizontal unit

Whether the water heater is offered as a wall-mounted, floor-standing or floor-standing unit depends primarily on the size of the unit.

Small units can be mounted unobtrusively on the wall to save space. Larger units are usually offered as standing or lying units or, in a particularly space-saving design, as a flat tank.

Flat storage cylinders are characterised by their shallow depth and are therefore the best choice if there is only limited space available for installing a water boiler.

Unpressurised or pressurised

Hot water boilers are offered in two fundamentally different designs:

  • Closed, pressure-resistant hot water boilers
  • Open, pressureless hot water boiler

With closed and therefore pressure-resistant devices, the water can be drawn off at several taps.

The storage tank of closed boilers is directly connected to the water pipe and thus exposed to a pipe pressure of up to 10 bar. The installation of normal high-pressure fittings is possible here.

Open, unpressurised hot water storage tanks supply a single tap and require a special low-pressure fitting. The supply is made via a special low-pressure mixer tap.

When the valve is open, water flows into the storage tank from below at reduced pressure. At the same time, the mixer tap serves as an overflow for water quantities that occur due to expansion during heating.

Energy demand

The energy requirement and thus the expected costs for operating a hot water boiler depend on various factors:

  • Size of storage tank
  • Actual water consumption
  • Temperature (initial and final temperature)
  • Insulation of the storage tank

The demand and thus the optimal size of a hot water boiler are very individually dependent on the habits of the user and are based on the size of the household.

The energy consumption for heating the water depends on the difference between the supply temperature and the selected final temperature. For heating by about 50 °C, an energy requirement of 0.06 kWh per litre of water can be assumed.

The insulation determines how often a unit must switch from standby to heating mode in order to keep the water in the storage tank constantly at the selected temperature.

Did you know that electrically operated hot water tanks use almost 100 % of the electrical power when heating. Losses occur due to heat transfer through the thermal insulation. In addition, when assessing the efficiency of electrically operated hot water boilers, it must be taken into account that electricity generation varies in efficiency depending on the type of power plant.

Facts worth knowing about water heaters

How do I connect a water heater correctly?

Here we have selected a suitable video for you on the subject of installing a hot water boiler. The boiler in the video is a small tank with an undersink design. The video offers tips and tricks for installing a hot water boiler.

You should always have the installation of non-plug-in appliances carried out by the respective manufacturer or a specialist company.

How do I descale my water heater and why is it so important?

Limescale is deposited on the heating coils of the hot water boiler, especially when the tap water is hard. This reduces energy efficiency, can cause dangerous bacteria and, in extreme cases, can even damage the appliance. For these reasons, it is very important to decalcify the hot water boiler regularly.

Hot water boilers without a cleaning opening should be descaled by experts. You can remove limescale from boilers that have such an opening yourself. To do this, get new seals, suitable tools, possibly a new protective anode and a hose that reaches from the hot water boiler to the drain.

Here we have selected a video summarising the topic of descaling the hot water boiler:

Here is a step-by-step guide on how best to proceed with descaling:

  1. Disconnect the water heater from the mains and shut off the water supply.
  2. Drain all the water from the boiler. To do this, attach the hose to the drain valve.
  3. Now you can open the cleaning opening and pull out the heating rod.
  4. You can now roughly remove limescale and sludge from the heating rod, the storage channels and the inner walls using wood.
  5. The inner walls and the heating rod can now be thoroughly decalcified with decalcifier or alternatively with diluted vinegar essence or citric acid.
  6. If necessary, replace the protective anode.
  7. Once everything is clean, you can reassemble the boiler and connect it to the water and electricity supply.

To prevent the heating element from burning out, do not reconnect the power until the storage tank is filled with cold water.

Image source: Catalog