Last updated: August 5, 2021

Do you not need hot water very often in your household and would like to save the costs of permanently heating the water without any sense? Then you should replace your boiler, which constantly heats water, with an instantaneous water heater.

What are the advantages of an instantaneous water heater over a boiler? How much does it cost to buy one and how do you install it? Answers to the most frequently asked questions can be found here in the big instant water heater test 2021.

We present the best instant water heater products and want to help you with your purchase decision. In addition, you will find helpful tips and tricks in our guide on which instant water heater is best for you. Regardless of whether you ultimately decide on an electronic or hydraulic instantaneous water heater, we will tell you about the advantages and disadvantages of each model.




Summary

  • An instantaneous water heater is needed to prepare fresh hot water. Unlike a boiler, an instantaneous water heater does not heat the water until the tap is opened.
  • The instantaneous water heater is particularly practical if hot water is not often needed in a household. In this case, you can save a lot of money with this appliance.
  • Important criteria such as size, workmanship, output, weight, intended use and features should be considered when buying an instantaneous water heater.

The Best Instantaneous Water Heater: Our Choices

Guide: Questions you should ask yourself before buying an instantaneous water heater

What is an instantaneous water heater and how does it work?

Instantaneous water heaters are permanently installed devices for heating water. They heat the water only when the tap or the point of use is opened. Due to the high heat output, hot water can be produced continuously. Instantaneous water heaters are used in decentralised water supply, for example in the kitchen or bathroom.

In which cases is an instantaneous water heater useful?

Instantaneous water heaters are ideal,...

  • if there is no space on site for larger storage tanks that store hot water over a longer period of time
  • if hot water is not needed regularly in buildings or parts of buildings
  • if only a small budget is available, and
  • if it is important that hot water is available immediately when needed

What are the differences between an instantaneous water heater and a hot water storage tank?

When it comes to providing hot water, the central question is: Is it more sensible to use a hot water storage tank (closed or pressure-resistant, open or unpressurised) or an instantaneous water heater?

If it is important to you to have hot water as soon as you turn on the tap, if you want to waste as little energy as possible in providing it and if the place of use is in a location where no huge quantities of hot water are needed - then the instantaneous water heater is the best choice for you.

Provides your hot water: the instantaneous water heater. (Photo: reverent/ pixabay.com)

Hot water tanks are used to produce, supply and store hot water. These so-called boilers exist - depending on the area of application - in large or small variants.

Storage tanks with a volume of 5 to 15 litres are used to produce hot water in kitchens or bathrooms, while storage tanks with a larger volume are used, for example, in showers or bathrooms. Both variants are connected directly to the tapping point.

Hot water storage tanks are available in both unpressurised and pressurised versions. Instantaneous water heaters are used to produce and supply hot water. When the tapping point is opened, the instantaneous water heater switches on and produces hot water immediately. In contrast to a conventional hot water tank, an instantaneous water heater does not store heated water. This prevents the waste of unnecessary energy in many cases.

What are the advantages of an instantaneous water heater compared to a conventional hot water storage tank?

Instantaneous water heaters are best suited for heating water in small quantities, for example in flats and parts of buildings where the demand for water is rather low. The great advantage of instantaneous water heaters is the elimination of supply losses (since hot water is only produced when it is needed). Similarly, instantaneous water heaters are cheaper to purchase than large-volume hot water tanks, which often saves money.

Hot water: essential for kitchens and bathrooms. (Photo: MikesPhotos/ pixabay.com)

What power do instantaneous water heaters have?

In the following, we show you what power different instantaneous water heaters can have:

Circuit breaker Tap quantity Electrical output in % of appliance output
Stage 1 Small 33 %
Stage 1 Small 66 %
Stage 2 Large 50 %
Stage 2 Large 100 %

How much electricity does an instantaneous water heater consume?

Unfortunately, no general statement can be made here either. It depends entirely on the amount of water to be heated. The more hot water you need, the more electricity it consumes. The manufacturers' power specifications only indicate the amount of water that can be heated at the same time.

How does the installation work?

An instantaneous water heater may only be connected and put into operation by a specialist company. The water heater is installed on the existing water and electricity connections on site.

What does an instantaneous water heater cost?

That depends on what kind of product you choose. Ordinary instantaneous water heaters are available from around 150 euros in some online markets. For small instantaneous water heaters, the price starts at 125 euros.

However, if you want a product from a well-known manufacturer that offers you its service and quality afterwards, which can also be conveniently operated via an LCD display, such a device can easily cost between 400 and 600 euros, in some cases even more.

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

Basically, you can distinguish between two different types of instantaneous water heaters:

  • Electronic instantaneous water heaters
  • Hydraulic instantaneous water heater

An instantaneous water heater is used to heat water. The boiler is a contrast to the instantaneous water heater, as it provides a limited amount of water in a storage tank. In contrast, the permanently installed instantaneous water heater only heats the water when a tap is opened.

Instantaneous water heaters have a very high heating capacity, so that the incoming cold water is heated directly as it flows through. This means that there is no need for a hot water tank at all. The instantaneous water heater is particularly useful if hot water is not often needed in your household. That's why you can save a lot of money with an instantaneous water heater. In some online markets, ordinary instantaneous water heaters are usually available from around 150 euros.

Important criteria such as size, workmanship, performance, weight, intended use and equipment also play an important role in the purchase and should also be taken into account. In the following section, we would like to give you an overview of the two different types of instantaneous water heaters.

In addition, we will briefly explain the respective differences to help you find out which instantaneous water heater is the right one for you. The advantages and disadvantages of each type are clearly presented for comparison.

How does an electronic instantaneous water heater work and what are its advantages and disadvantages?

The electronic instantaneous water heater has an inlet temperature sensor and a flow sensor. With this type of instantaneous water heater, the water temperature can be selected on the appliance beforehand, which eliminates the need to add cold water. In addition, the electronic instantaneous water heater heats the water independently of the water pressure.

Depending on the desired temperature, the heating power is switched on continuously via fixed programmed values. Many models also have a remote control so that you can easily set the desired temperature at the touch of a button. The advantages of electronic instantaneous water heaters lie clearly in their convenience and better efficiency, which enables energy savings of up to 20 percent compared to hydraulic instantaneous water heaters. The disadvantage of electronic instantaneous water heaters is the purchase price, as this is usually higher than for hydraulic models.

Advantages
  • Works much more efficiently
  • Desired temperature possible
  • Energy-saving
  • Great comfort
Disadvantages
  • Higher purchase price

Two subgroups of electronic instantaneous water heaters are fully electronic and partially electronic instantaneous water heaters. The fully electronic instantaneous water heater has an almost constant temperature without fluctuations.

The water quantity and the automatic adjustment of the electrical heating output are monitored via sensors and the motor valve. After monitoring, the fully electronic instantaneous water heater determines whether the heat output was correct. If the heat deviates from the required temperature, the instantaneous water heater adjusts its output accordingly within a few seconds.

The semi-electronic instantaneous water heater also works with sensors that monitor the incoming cold water and the flow rate. Based on the two measured values, the semi-electronic instantaneous water heater adjusts its output according to a pre-programmed formula.

How does a hydraulic instantaneous water heater work and what are its advantages and disadvantages?

The hydraulic instantaneous water heater works a little differently because the hydraulic instantaneous water heater regulates the hot water production via the water flow through the water pipe.

For example, if you open the tap a little, the first stage of the instantaneous water heater switches on and heats the water. If the tap is opened further, the flow rate increases. The hydraulic instantaneous water heater then switches to the second stage and heats the water.

Advantages
  • Favourable purchase
Disadvantages
  • Greater energy consumption
  • temperature fluctuations

The disadvantage of the hydraulic instantaneous water heater is the temperature fluctuations. If the water pressure fluctuates, so does the temperature. The result is frequent readjustment. However, there are also more modern hydraulic instantaneous water heaters with more than two stages. These models are much more energy-efficient and usually have three times as many stages.

Did you know that there are also gas-powered instantaneous water heaters? However, these devices usually take up more space and usually cannot boil water, unlike water-storing boilers.

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

In the following, we would like to show you which factors you can use to compare and evaluate instantaneous water heaters. This should help you decide whether a product is suitable for you or not. In short, these are the following criteria:

  • Output
  • Intended use
  • Weight
  • Comfort / Equipment
  • Quality
  • Size

In the following text you can get an overview of what the individual criteria mean and how you can make a decision based on them.

Performance

As with other electronic items, power is important here: it indicates how much water can be heated to a certain temperature in a certain amount of time.

For example, if several people live in the same household and use the same appliance, a water heater with a higher output is recommended.

Intended use

The most important decision criterion: for what purpose do you need your instantaneous water heater? Do you only want to use hot water for washing up in the kitchen or do you also want to take long, hot showers? Or perhaps both at the same time? If so, it is advisable to supply several taps at the same time.

Supplying several taps at the same time allows you to shower and use the hot water tap in the kitchen at the same time. (Photo: 955169 / pixabay.com)

Weight

This is actually a rather negligible decision criterion. Even though you should consider the weight because of the different mounting options, we would pay a little less attention to this point.

Comfort / Features

You should also think about the features. Most instantaneous water heaters allow you to set the temperature to the exact degree Celsius. In some cases, this can even be done conveniently by remote control. Most products also have a digital temperature display, which makes operation much easier.

Quality

If you use a device from one of the most popular manufacturers - AEG, Siemens, Vaillant, Junkers, Stiebel Eltron or Clage - it is almost impossible to make a wrong purchase. A warranty claim, for example, is definitely not denied by these manufacturers.

Size

Size is an important criterion, especially for instantaneous water heaters. Connections that have already been laid and prepared must fit exactly. The appliance should also not be covered by furniture, so that easy operation is guaranteed at all times.

Facts worth knowing about instantaneous water heaters

How does an instantaneous water heater work?

The water flows through the cold water connection and through the water strainer to the water quantity regulator. This compensates for the influence of pressure fluctuations from the mains supply and thus keeps the water flow and thus the temperature increase as constant as possible. The water flowing through creates a differential pressure between the chambers below and above the membrane in the water switch via the Venturi nozzle.

Depending on the amount of water flowing through, the flow switch is actuated by the membrane. With small water flow rates, three of the four heating coils are switched on. With larger tapping quantities, the flow rate increases and thus the differential pressure in the water switch. A higher unit output is released at the flow switch. In the heating block, the water flowing through is heated directly at the heating coils.

When the unit is switched off, the hot water tap valve is closed, the differential pressure in the water switch is reduced and the flow switch interrupts the circuit. If this cut-off fails to occur, pressure builds up in the heating block because the non-return valve shuts off the water passage in front of the safety switch. The excess pressure acts on the diaphragm of the safety switch, whose switching contacts immediately interrupt the power supply to the heating coils.

How long have instantaneous water heaters been around?

The engineer Hugo Junkers applied for a patent for his gas bath heater in 1894. This was much larger than the instantaneous water heaters we know today, although it was based on the same principle.

Over the decades, of course, this technology was continuously developed until an electrically operated instantaneous water heater emerged from a gas bath heater. Today, you can find instantaneous water heaters in countless households, often the size of a shoebox. They are usually powered by electricity.

How do I descale an instantaneous water heater?

  • First, disconnect all electricity, gas and water supply lines from the unit!
  • Now the appliance is dismantled and disassembled into its individual parts.
  • The calcified components are soaked in an acid bath (for a few hours, or even a few days in case of hardship!).
  • Before using the appliance again, it should be completely rinsed once to remove all acid and limescale residues.
  • There should no longer be any white deposits inside the unit.

The appliance should be decalcified at the latest when the function of the instantaneous water heater is impaired by hard water and, for example, no longer provides hot water for the shower or bathtub.

Picture credits: Pixabay.com / Seregas

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