Last updated: August 5, 2021

Welcome to our large hot water tank test 2021. Here we present all the water heaters that we have tested in detail. We have compiled detailed background information for you. 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.

Furthermore, you will also find some important information on this page, that you should be aware of if you want to buy a hot water tank.

Contents




Summary

  • A hot water tank is a permanently installed device and allows you to produce as well as store hot and warm water.
  • There are two main groups of boilers: the closed, pressure-resistant ones and the open, pressureless ones. Both types come in different sizes and installation variants.
  • Most hot water boilers are operated with conventional electricity. More and more models, however, are being coupled with solar operation in order to protect the environment and your wallet.

The Best Hot Water Tank: Our Choices

Guide: Questions you should deal with before buying a hot water cylinder

How does a water heater work?

As you may know, the name of the hot water tank as boiler comes from the English "to boil", which means to boil. This designation thus already describes the basic principle of the function of all water heaters. In simple terms, a hot water tank is a somewhat larger kettle - cold water is poured in, heated up to a certain temperature and can then be used as desired. This example also shows that, in contrast to a central hot water supply, the treatment takes place close to, if not directly at, the point of use.

Directly heated boiler

In a closed, pressure-resistant hot water tank with its own heating burner, the energy generated by the burner passes through the tank in which the domestic hot water is stored to the flue gas connection and releases the heat during this process. As soon as the temperature falls below the preset value, the burner becomes active again.

To prevent the heated water from flowing back into the inflow, this type of boiler must be installed with a non-return valve. In addition, a safety valve must be fitted to allow the water, which expands as it heats up, to drain out if necessary and prevent overpressure.

Indirectly heated boiler

In an indirectly heated hot water tank, there is a spiral-shaped pipe (made of copper or stainless steel) in the tank that is surrounded by the domestic water. The heating water flows through this pipe into the storage tank with the help of a pump and thus heats the surrounding water while it cools down itself.

Because of this heat exchange, the pipe is also called a heat exchanger. This heating of the domestic water is also called charging, and the pump that pumps the heating water through the pipe is correspondingly called a charging pump.

The desired temperature of the hot domestic water can be pre-selected either by means of a controller on the heating system itself or with the help of a thermostat. If the temperature falls below the set value, the heating starts to heat up until the corresponding value is reached again.

The hot water tank ensures that there is a supply of warm and hot water in your home. There are directly and indirectly heated water storage tanks as well as closed, pressure-resistant and open, pressureless ones. (Picture source: 123rf.com / 55845687)

What energy sources do hot water tanks use?

Whereas in the past it was still necessary to heat water by hand in order to have hot water available, in most of the world today it is somewhat easier. Of all the known energy sources, solar energy, electricity and gas are the main ones used for hot water tanks, although the source differs depending on the size of the boiler.

For smaller water heaters, an electric source is preferred nowadays, in contrast to the earlier gas. Larger boilers are also mainly powered by electricity or gas, and only newer models have a special device to allow additional heating by solar energy.

Electricity

Smaller water heaters have a metal-sheathed heating element in the casing that heats the surrounding water by converting the supplied electricity into heat energy. Normally, a connected load of 2,000 watts is required for small boilers, so they can simply run off the regular electricity supply. Larger boilers logically require more electricity, which is why they are usually operated via night-time electricity in order to keep costs as low as possible.

For this purpose, the heating phases are scheduled to the cheapest times of the electricity provider, which in most cases applies at night. In order to minimise the heat loss of the heated domestic hot water, from the time of heating until effective use during the day, such storage tanks are very well insulated and have the highest possible maximum temperature.

Gas

Today, gas is rarely used as an energy source for small hot water storage tanks and is mainly used for larger boilers in detached houses with gas heating. Larger hot water tanks have a connection option for commercially available propane gas cylinders, while smaller ones (for example in camping) use a heating element with a gas burner.

Solar energy

Hot water tanks based on solar energy are devices in which the solar tank, boiler and heating circuit are integrated. In summer, the hot water demand of a single-family house can be covered by solar collectors, which support the heating system in winter.

This requires collectors, a solar storage tank with temperature controller and, if necessary, a heating system. Solar storage tanks, also called solar hot water buffer tanks, store the heat so that hot water is available even without sunshine. The stored heat is then used as domestic hot water or for space heating. Since the sun does not always shine strongly enough, the temperature of solar-powered boilers is usually set much higher than that of electricity-powered ones.

When the water is dispensed, cold water is added to the 80 °C to 90 °C hot water through a thermostatic valve in order to reach the desired consumption temperature. The conventional heating only starts when the hot water produced by solar energy has been used up. This can greatly reduce energy costs.

Where is a hot water tank most often used?

Smaller boilers (5 to 15 litres) are often installed directly by sinks or washbasins if there is no central hot water supply or the distance to it is too great (energy loss and increased risk of legionella formation). Larger hot water storage tanks (70 to 200 litres) are often used as the sole hot water supply for individual residential units.

What types of hot water storage tanks are there?

The smaller versions of boilers are mounted directly above or below the point of use, on the wall. These forms are accordingly referred to as over-the-sink or under-the-sink forms. Larger hot-water cylinders are also available as wall-mounted or floor-standing or even as so-called flat cylinders. The classic form, however, is the upright cylinder, as this is the best from the point of view of energy efficiency.

Which type and size of hot water cylinder is the most environmentally friendly?

This again depends on your personal consumption and requirements for the hot water tank. Of course, a boiler with solar energy as an optional source is more environmentally friendly than one that runs purely on electricity or gas. A good insulation of the storage tank as well as the positioning of the boiler increase the energy efficiency considerably.

Regardless of the level of insulation, hot water tanks benefit from a warmer environment, for example near a heat source.

How long is the service life of a hot water tank?

Due to calcification and the resulting increased risk of bacteria formation, it is not advisable to keep a hot water tank in its original condition throughout its service life. On average, this is 15 to 20 years, depending on the model. In terms of energy efficiency and environmental friendliness, it is always worth taking a look at the latest models.

What are the advantages of a hot water tank over an instantaneous water heater?

In the following, we list the advantages of a hot water tank compared to an instantaneous water heater:

Hot water tank instantaneous water heater
Advantages - Simple models already available at very low prices - Constant water temperature of the entire domestic water volume - No water loss due to "warm-up" - Shorter waiting time until the desired water temperature is reached - Low standby loss - Theoretically unlimited quantity of hot water, without time delay - Less hygienic, as there is no stored water - Compactness
Disadvantages - Higher energy consumption in the long run - Waiting time to reach target temperature first time - Limited capacity - Hygiene loss if water is left to stand for longer - High energy consumption during use - Temperature fluctuations, (especially in models without flow-dependent control) - No possibility of reducing electricity costs

What are the alternatives to a hot water tank?

In addition to hot water storage tanks, there is also the option of heating your water with an instantaneous water heater. In contrast to the boiler, the instantaneous water heater does not contain a drinking water storage tank and is therefore more compact in size. The instantaneous water heater is connected to the cold water pipe in the same way as the boiler, but it works differently in that it is connected directly to the tap.

It heats the water as soon as the tap is opened, for example, and stops heating when the tap is closed again. This is done by directing the flowing cold water along a heating element and thus heating it. Apart from their compactness, instantaneous water heaters do not differ in shape from conventional hot water tanks. Small and medium sizes prefer to run on electricity, while medium and large ones run on gas.

What are the costs of a water heater?

An accurate cost calculation for the purchase and use of a boiler can only be made when the following factors are known:

  • The required or real water consumption of the object to be supplied
  • The size of the boiler required
  • The desired temperature of the water (initial and final temperature)
  • The insulation of the boiler

You should note that using an electricity source for your water heater is more expensive than using alternative sources (gas, oil, district heating, etc.).

To give you a rough idea of the price trends of new boilers, you will find some information listed here. If you want a closed, pressure-resistant hot water tank, you should expect prices from 110 to 320 euros for a 15-litre capacity. For a 100-litre capacity, prices range from 340 to 460 euros.

The average consumption of water in the household should be taken into account when buying. (Image source: unsplash.com / John Cameron)

If, on the other hand, you want an open, pressureless boiler, you can expect to pay only around 60 to 70 euros for a 15-litre volume. With a 100-litre volume, however, you will have to reckon with around 450 euros.

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

Boilers are generally divided into two main groups, whereby a somewhat differentiated subgroup can also be named for the second:

  • Closed, pressure-resistant, direct-heating hot water tanks
  • Open, pressureless, indirect-heating hot water storage tanks
  • (double-shell storage tank)

For many of us, a hot bath or shower crowns our daily routine of relaxation after a long day or a hard night's sleep. But how do we get this privilege of instant hot water? It's a question many people only ask themselves when suddenly there is no hot water flowing after all.

Unless you live in a block of flats with a central water supply or in a secluded cottage with a wood-burning stove, chances are good that your hot water is also produced and stored by a hot water tank. A hot water storage tank (also called a boiler) is a technical device that processes hot water and, as the name suggests, stores it for later use. Synonyms such as drinking water storage, domestic hot water storage or buffer storage are also often used.

These devices are usually made of stainless steel, copper or steel, or enamelled, and can basically be divided into two groups based on their operating mode.

What are the operating modes for hot water storage tanks?

Hot water tanks are mainly differentiated based on the method by which the water is heated. There are so-called closed, pressure-resistant hot water tanks, which heat directly, and open, pressureless hot water tanks, which heat indirectly.

Closed, pressure-resistant, direct-heating hot water tanks

Direct-heating hot water tanks are both heat generators and heat storage tanks in one. The devices generate their heat directly within their storage tank and have a built-in heating burner as well as a flue gas connection for this purpose.

This also means that they are independent of the central heating system. The storage tank is directly connected to the water pipe and thus exposed to a pressure of up to ten bar - hence the required pressure resistance of the boiler.

Advantages
  • Independence from central heating system
  • Supplies several taps
Disadvantages
  • Low energy efficiency
  • High maintenance costs
  • Complex design
  • Additional exhaust gas production

This type is always enamelled and is operated with electricity or gas. As standard, these boilers hold 30 to 120 litres and were previously used as a group supply for several taps in the bathroom or as the central domestic hot water source.

However, since this type of boiler offers low energy efficiency and involves high maintenance costs, it is rarely installed nowadays.

Open, pressureless, indirect-heating water heaters

In indirectly heating boilers, the (storage) water is heated continuously with the help of the heating water that comes from the boiler. The boiler therefore does not have its own heating burner - the heating system used to increase the room temperature is also the boiler for the hot water. Therefore, no additional chimney connection is required when using such hot water boilers, as no flue gases are produced.

Advantages
  • No additional flue gases
  • No additional chimney connection required
  • Hot water available at all times
  • Simple construction
  • Favourable purchase price
Disadvantages
  • Small barrel capacity
  • Supplies only one object

This type of boiler has a capacity of around 5 to 15 litres and is therefore mainly suitable for supplying individual properties. In contrast to directly heating hot water tanks and instantaneous water heaters, hot water is available at all times and solar thermal systems also generally use an indirect boiler.

Pressureless hot water storage tanks are generally simpler in design and cheaper than pressurised ones, as they are not exposed to the water pressure of the water pipe.

Double-shell storage tank

As a little bonus, here is another type or subcategory of indirectly heated water storage tank. Double-shell hot water storage tanks, or double-shell storage tanks for short, are a storage-in-storage design in which the (domestic) water in the inner tank is heated by the heating water in the outer tank. The storage wall of the inner storage tank serves as a heat exchanger.

Advantages
  • Even simpler construction
  • even more favourable connection price
Disadvantages
  • Low efficiency
  • Needs additional heating

Although open, unpressurised boilers are already simpler in their construction than closed, pressurised ones, double shell boilers are even simpler and 20 to 50 percent cheaper in terms of purchase price. However, since their efficiency is lower, they are usually offered in combination with other heating options (oil, gas, wood, etc.).

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

Basically, the most important points of consideration when buying a boiler can be summarised as follows:

  • Type of installation
  • Dimensions
  • (Heating) output
  • Average power consumption
  • Maximum temperature
  • Capacity
  • Item weight
  • Energy efficiency class
  • Maximum permissible pressure
  • Child safety lock

In most cases, buying a smaller, open water heater is the best decision.

Smaller boilers have the advantage of quick and relatively uncomplicated installation, and they also have a longer service life.

If you decide to buy a hot water tank with a capacity of around 5 litres, you should pay special attention to the heating times so that you really always have hot water stored and available. These vary depending on the boiler, but on average they are 15 to 35 minutes.

Modern water heaters are usually very well insulated and therefore consume less electricity. The price of the appliance itself should not be your main criterion, as slightly more expensive appliances make up for their extra cost with lower electricity consumption.

Type of installation

Depending on your taste and requirements, you are free to choose between different forms or installation types of hot water tanks. You will find out which types there are a few lines further down. The important thing now is to decide which one you want or which one you can use at all. In small flats or cramped spaces, the installation of a small cylinder with an under- or over-the-table installation is more suitable than that of a floor-standing or wall-mounted cylinder.

If you want to buy a larger hot water tank, you should also consult a professional. They will have the knowledge to recommend the most suitable boiler for your home and needs, and will usually take care of delivery and installation. Sometimes he can add little extras, such as a radio or Bluetooth speakers, depending on the installation location.

Dimensions

When it comes to dimensions, you should make sure that you know where you want to or will install your hot water tank and how much space you have available there. In terms of energy efficiency, cylinder-shaped water heaters are recommended because they heat the water evenly and keep it warm.

In angular shapes, on the other hand, heat is lost in the respective corners, which affects the temperature of the entire filling quantity and its reheating.

Limescale deposits reduce performance. Measurable improvements can be achieved by descaling. (Picture source: 123rf.com / 28040229)

(Heating) performance

On average, the output of smaller hot-water tanks is 2 kilowatts and of medium to large boilers 4 to 6 kilowatts. The models presented here are all in these ranges as well.

However, the heat output alone does not indicate the final electricity consumption when using the hot water tank, because a high output consumes a lot of electricity for a short time, while a low output consumes little but over a longer period of time. So in the end this balances out and there is the same electricity consumption for both.

Average power consumption

Some suppliers even note the average power consumption of their product per year or per day in their product description. These values are calculated for operation in standby mode and are intended to give you a rough idea of what you can expect to pay if you use this product. The power consumption is determined by the amount of water used and the set temperature.

Even if no hot water is flowing, the boiler keeps the stored water at a certain temperature and heats up again and again. How often this happens depends on both the insulation of the hot water tank and the set temperature. A lower temperature means less temperature loss and therefore less electricity consumption to compensate for this by reheating.

In general, smaller appliances with a capacity of up to 5 litres are cheaper to consume and older models are more expensive if they are not supplied by cheaper electricity (for example, night-time electricity).

Maximum temperature

Although the maximum temperature is stated, it is unlikely that you will ever use it. This is because the higher the water temperature, the higher the degree of calcification within the storage tank and pipes. Furthermore, a high temperature setting leads to additional electricity costs in winter, as the even colder cold water has to be heated up.

The temperature can usually be set on the unit itself using a manual or digital controller. For an average normal consumption of hot water, a setting of 55°C is sufficient, although the weekly one-time heating up to over 60°C, to combat bacteria, should not be forgotten.

Capacity

Only you know how much hot water you and your family will need or consume. However, it is assumed that a boiler with a capacity of 150 litres is sufficient for a household of four people with normal hot water use.

However, the exact size required depends on the individuals themselves and their habits, as well as on the location to be supplied.

So when calculating your required storage capacity, you should also consider when, for example, you and your flatmates shower. If the hygiene routine takes place at different times, a medium-sized boiler can be sufficient even for four people.

However, if everyone takes a shower at the same time or one right after the other, the hot water will only be enough for the first two people, unless you have a large storage volume. However, a capacity that is calculated too large is also not recommended, as this leads to extended storage times of the hot water and this can lead to the formation of bacteria (for example legionella).

As already mentioned, the capacity of a hot water tank also plays a significant role in the electricity consumption and therefore the costs after the purchase of the appliance. Larger quantities of water require a larger storage tank, with a larger surface area. This in turn provides more surface area for heat loss and therefore requires increased heating.

Item weight

Sometimes the living walls, especially in apartment buildings, are not very solidly built and can therefore only be loaded or resist up to a certain weight. You should always remember that the item weight is only the minimum weight, as you will still be filling your hot water tank with water.

If you need a larger capacity water heater but are not sure if your intended installation location will withstand it, be sure to consult a professional. With smaller capacities, this should not be a problem, as such boilers rarely exceed the 5 kg limit.

Energy efficiency class

Mother Nature and future generations will thank you if you think about the environment today. If you want to try to minimise your impact on the environment and your wallet, you should also pay attention to the energy efficiency class of the hot water tank on offer.

A good classification consumes less electricity, for example, and therefore causes lower costs and fewer pollutant emissions, which has a positive effect on the environment.

Since the beginning of 2017, no water heaters with an energy efficiency class of D or lower may be sold and the currently best models belong to class A+. In addition, higher-quality models have a setting option for energy-efficient use, which can save electricity and therefore costs.

Technology that is as new as possible and good insulation contribute to good energy efficiency. In addition, a responsible, individual setting of the temperature range can support this. Of course, if you are not going to use your hot water tank for a longer period of time, you should switch it off - for reasons of cost as well as hygiene.

For infrequent, repetitive use, a timer can save energy. However, you must be aware of the possible risk of frost.

Maximum permissible pressure

This point is particularly important for closed, pressure-resistant boilers. Since these have a constant connection to the water pipe, an internal pressure is created in the closed hot water tank. In order not to exceed the tolerance limit by mistake, it is important when buying such a boiler to know what pressure your water supply is at and what pressure your new boiler can handle. Nowadays, hot water boilers should be able to withstand a maximum pressure of 10 bar.

Child safety lock

If you are looking for a water heater for your family and there is a small child or a person with limited cognitive abilities in the family, you should also make sure that your water heater has a built-in child safety lock or safety valve. These can not only significantly reduce the risk of scalding, but also prevent unnecessary hot water consumption.

Facts worth knowing about hot water storage heaters

How long have hot water tanks been around?

The ancient peoples, above all the Romans and Greeks, already knew how to produce and store hot water. Today, only ruins bear witness to the colossal thermal baths of the Roman people, which were spread across the Eurasian continent These became very popular after the 1st century AD, but baths had also been known to the Greeks before that, only on a smaller scale.

The Roman baths were heated and supplied with hot water through a system of channels filled with hot air, the so-called hypocaust.

What is the ideal temperature setting for a hot water tank?

Human skin runs the risk of burning at 55 °C already. Depending on personal preference, temperatures in the 30 to 40 °C range are perceived as pleasantly lukewarm. Based on these findings, a temperature setting of 60 °C is recommended for private households. Higher temperatures than this lead to increased calcification and increased energy loss.

What is the average amount of hot water needed per person?

An average consumption of 40 litres per person per day is assumed.

How do I ensure good hygiene of my hot water tank?

In order to guarantee the hygienic standard and the quality of the drinking or service water, hot water tanks are made of enamelled steel or stainless steel.

Stainless steel is particularly durable because it is extremely corrosion-resistant. Enamelled steel storage tanks, on the other hand, are more susceptible to corrosion, as the enamel often has imperfections or wear points.

They therefore require extra protection, which can be provided by using so-called impurity/protective or sacrificial anodes. External anodes are very robust, but sacrificial anodes are mainly made of magnesium and must therefore be checked again and again depending on the water quality and replaced if necessary.

If your hot water (20 to 55 °C) stands still for a longer period of time (several hours to days) in the storage tank as well as in the pipes, this increases the risk of legionella multiplying to a number that is harmful to your health. To prevent this, it is recommended to heat the hot water to at least 70 °C once a day to ensure thermal disinfection of the water.

Picture credits: Pexels.com / Kaboompics .com

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