Best Water Heater: Review & Recommendations

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Don’t you need hot water in your household very often and would like to save the costs for the permanent, pointless heating of water? Then you should replace your boiler, which continuously 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 great instantaneous water heater Test 2020, where we introduce you to the best instantaneous water heater products and want to help you with your purchase decision. You will also find helpful tips and tricks in our guide to help you decide which instantaneous water heater is best for you. Whether you decide to buy an electronic or hydraulic instantaneous water heater, we will explain the advantages and disadvantages of each model.

The most important facts in brief

  • An instantaneous water heater is required for the preparation of 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 when 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, performance, weight, intended use and equipment should be considered when purchasing a continuous flow heater.

Instantaneous water heater test: editorial favourites

  • The best electronically controlled instantaneous water heater
  • The best pressureless small accumulator
  • The best mini instantaneous water heater
  • The best small hydraulically controlled instantaneous water heater

The best electronically controlled instantaneous water heater

The electrically controlled instantaneous water heater from Stiebel Eltron is suitable for supplying hot water to several taps and can therefore supply the bathroom and kitchen simultaneously. With a three-stage temperature selection and high energy efficiency, the pressure-resistant instantaneous water heater meets energy class A.

The simple connection of the instantaneous water heater and its energy-saving heating convinces many buyers. In addition, the long shelf life of the product and the individual regulation of the water temperature score points with many customers.

The best pressureless small accumulator

With infinitely variable temperature selection, the pressureless AEG small storage tank with a capacity of 5 litres is ideal for washing dishes in the kitchen, but also for installation in the bathroom. Due to its high-quality thermal insulation and energy-saving position, the Durchlau

The courteous customer service and the simple assembly convince numerous customers. In addition, the device is also enthusiastically received by buyers due to its efficiency, resource savings and individual regulation of the water volume.

The best mini instantaneous water heater

Measuring 15 x 7.5 x 13.5 cm, this instantaneous water heater is the smallest compared to other appliances. The weight of 898 g is also impressively low.

This storage unit requires a 230 V power connection, and can therefore be easily connected to the mains supply via a permanent connection, as long as this connection is protected with an extra 25 A fuse. The capacity of 5 kW corresponds to the average of all small instantaneous water heaters.

The best small hydraulically controlled instantaneous water heater

With the dimensions of 14.3 x 19 x 8.2 cm the device turns out to be very small. With the weight of 1.4 kg it is in the average range of small instantaneous water heaters.

With an output of 3.5 kW, it is in the low range, so it makes sense if you want to use it to provide maximum hot water for a sink or hand wash basin, for example. […]

In concrete terms, this means for you that the device is optimally suited for small water requirements, for example in the cellar, guest bathroom or kitchen.

Advisor: Questions you should deal with before you buy an instantaneous water heater

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

Instantaneous water heaters are permanently installed devices for hot water preparation. They do not heat the water until the tap or draw-off point is opened.
The high heat output means that hot water can be produced continuously. Instantaneous water heaters are used in decentralised water supply systems, for example in kitchens or bathrooms.

Sönke Eisbacher expert at hausbau-tipps.info
New high quality gas flow heaters ignite by battery or generator ignition. And that without electricity and only when needed. However, the efficiency is only about 80 percent compared to the electric drive.
(Source: hausbau-tipps.info)

In which cases is an instantaneous water heater useful?

Instantaneous water heaters are ideal,

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

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

When providing hot water, you are faced with the central question: Is it more sensible to use a hot water storage tank (closed or pressure-resistant, open or pressureless) or an instantaneous water heater?
If you want to have hot water as soon as you turn on the tap, you want to use as little energy as possible to supply it and you want to use it in a place where you don’t need a huge amount of hot water, then the instantaneous water heater is the best choice for you.

Hot water tanks are used for the production, supply and storage of hot water. These so-called boilers exist – depending on the area of application – in large or also small variants.

Storage tanks with a volume of 5 to 15 litres are used for hot water preparation in kitchens or bathrooms, while tanks with a larger volume are used for example in showers or bathrooms.

Both variants are connected directly to the extraction point. Hot water tanks are available in both pressureless and pressure-resistant versions.

Instantaneous water heaters are used to produce and supply hot water. When the draw-off point is opened, the instantaneous water heater switches on and immediately produces hot water.

In contrast to a conventional hot water tank, a continuous flow heater does not store heated water. In many cases, this prevents the waste of unnecessary energy.

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

Instantaneous water heaters are best suited for producing hot water in small quantities, for example in apartments and parts of buildings or parts of buildings where the water demand is rather low.
The great advantage of water heaters is that they eliminate supply losses (as hot water is only produced when it is needed). Likewise, instantaneous water heaters are cheaper to buy than large-volume hot water storage tanks, which often saves money.

What output do instantaneous water heaters provide?

In the following we will show you what capacity different instantaneous water heaters can have:

How much electricity does an instantaneous water heater consume?

Unfortunately it is not possible to make a general statement here either. This depends entirely on the amount of water to be heated. The more hot water you need, the more electricity it consumes.
The manufacturers’ power rating only indicates how much water 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 at the water and electricity connections available on site.

How much does an instantaneous water heater cost?

That depends entirely on which 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 Euro.
However, if you want a product from a well-known manufacturer who will offer you his service and quality afterwards, which can be operated comfortably via 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 one is right for you?

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

  • Electronic instantaneous water heaters
  • Hydraulic flow heaters

An instantaneous water heater is used for hot water preparation. The boiler is in 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 cold water flowing in is heated directly as it flows through. This means that a hot water tank is completely unnecessary.

The instantaneous water heater is particularly useful if hot water is not often needed in your household. That is why you can save a lot of money with the 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. We will also briefly explain the differences between them to help you decide which type of instantaneous water heater is right for you. The advantages and disadvantages of the individual types 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 pre-selected on the appliance, eliminating the need to add cold water.

The electronic instantaneous water heater also heats the water independently of the water pressure. Depending on the desired temperature, the heating power is continuously switched on via fixed programmed values. Many models also have a remote control so that you can easily set your desired temperature at the touch of a button.

The advantages of electronic instantaneous water heaters are clearly the comfort and the better efficiency, which allows 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.

A monitoring of the water quantity and the automatic adjustment of the electrical heating power is carried out 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 then adjusts its output accordingly in a few seconds.

The partially 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 is slightly different in its operation, as the hydraulic instantaneous water heater regulates the hot water preparation by 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 flow heater then switches to the second stage and heats the water.

Advantages

Cheap purchase

Disadvantages

Greater energy consumption
Temperature Variations

The disadvantage of the hydraulic instantaneous water heater lies in the temperature fluctuations. If the water pressure fluctuates, the temperature also fluctuates.

As a result, frequent readjustments are necessary. However, there are also more modern hydraulic flow 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 fired instantaneous water heaters?
However, these appliances usually take up more space and usually cannot boil water, unlike water-storing boilers.

Purchase criteria: You can compare and evaluate instantaneous water heaters based on these factors

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

In brief, the criteria are as follows:

  • Performance
  • Purpose
  • 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, performance is important here: it indicates how much water can be heated to a certain temperature in a given time.

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

Purpose

The most important decision criterion: for what purpose do you need your instantaneous water heater? Do you only want to wash up with warm water in the kitchen or take a long, hot shower? Or maybe both at the same time? Then it is recommended to supply several taps at the same time.

Weight

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

Comfort / Equipment

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

Quality

If you use a device from the most common manufacturers – AEG, Siemens, Vaillant, Junkers, Stiebel Eltron or Clage – a bad purchase is almost impossible. A claim to warranty for example is definitely not denied by these manufacturers.

Size

Size is an important criterion, especially for instantaneous water heaters. Connections already installed and prepared must fit exactly. Likewise, the appliance should not be covered by furniture, so that you are always guaranteed easy operation.

Trivia: Worth knowing facts 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 effects of pressure fluctuations from the mains and thus keeps the water flow and thus the temperature increase as constant as possible.

The water flowing through generates 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 membrane actuates the flow switch.

In case of small water flow rates, three of the four heating coils are switched on. At larger tap volumes, 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 coil. When switching off, the hot water tap valve is closed, the differential pressure in the water switch is then reduced and the flow switch interrupts the circuit.

If this switch-off does not take place, pressure will build up in the heating block, as the non-return valve shuts off the water passage before the safety switch. The excess pressure acts on the diaphragm of the safety switch, via whose switch contacts the power supply to the heating coils is immediately interrupted.

Since when are instantaneous water heaters available?

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

Over the decades, this technology has of course been continuously developed further until an electrically operated instantaneous water heater was created from a gas bath oven. Today you can find instantaneous water heaters in countless households, often in the size of a shoebox. As a rule, they are operated with electricity.

How do I descale an instantaneous water heater?

  • First disconnect all power, gas and water supply lines from the unit!
  • Now the device 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 hardness!)
  • Before re-starting the unit, it should be rinsed once completely to remove acid and lime residues completely.
  • There must no longer be any white coating visible inside the unit.

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,

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