The best flat water heaters in the UK 2023

A water heater can make life easier, but it can also become a real source of clutter if it's not chosen properly. A solution that is accessible to small households: the acquisition of a flat water heater. A space-saving solution, it allows you to enjoy hot water all day long. Connected, with boost mode, extra-flat... this little guide will help you choose the right model.

Ariston Velis Evo - 50 L 1

Best value for money

Ariston Velis Evo - 50 L

The best flat water heater in 2021

With its 50 L capacity, this Ariston warmer is ideal for those who don't have much room. It combines several technologies that allow you to control the volume of water used.

255 £ on Amazon

Its compact design and rectangular shape make this Ariston Evo flat water heater a must-have for small homes. With its thickness of only 27 cm, it can be positioned vertically or horizontally for a considerable space saving. Its touch-sensitive control panel allows easy control of all parameters such as programming or heating temperature.

Thanks to the Eco Evo technology, you can save up to 15% on your bill. In addition, this model of water heater embraces the Nanomix function that separates hot water from cold water, as well as Shower Ready to have more visibility on the number of available showers. It is a designer appliance that is built to last over time.

Thermex IF Smart - 80 L 2

Best value for money

Thermex IF Smart - 80 L

The best entry-level flat water heater

With its compact size, this water heater adapts perfectly to all types of use. Offering a decent performance, it is ideal for small budgets that want to have hot water available all day long.

229 £ on Amazon

With its intermediate capacity of 80 L and its extra-flat design, this water heater can be integrated into any type of interior. It offers a correct energy performance thanks to its innovative insulation system. The intelligent Smart function allows you to constantly monitor the use of hot water. Moreover, it is a device that resists perfectly to corrosion thanks to the Bio-glasslined technology.

This flat water heater has a relatively fast heating time of 1 hour 45 minutes so that you can have hot water at 45°C. It offers ease of use with its intuitive control panel to activate the Smart function and adapt the temperature to your needs. By choosing this device, you will benefit from a self-diagnosis mode to detect any errors. It is also equipped with an excellent anti-frost system.

Atlantic Linéo - 80 L 3

Best value for money

Atlantic Linéo - 80 L

The best high-end flat water heater

This flat semi-accumulation water heater has all the technologies in terms of heating. Space-saving and economical, it can operate permanently and can be controlled remotely.

527 £ on Cdiscount

This Atlantic Linéo flat water heater adapts to the needs of the whole family thanks to its average capacity of 80 L. Designed to save space in small spaces, it can easily be installed in showers and kitchens to bring a modern touch to interior design. You can pair it with a mobile device to control it remotely via the Cozytouch app.

This device integrates 3 modes, Eco, Manual and Boost to better control hot water consumption and thus save on energy expenses. You can plug it in all day, and turn it off when you're away to avoid waste. Moreover, this water heater benefits from an efficient protection against corrosion.

Thermor Malicio 2 - 80 L 4

A great choice

Thermor Malicio 2 - 80 L

The best alternative for the family

Sleek design and fully functional, Thermor Malicio 2 has a connected function to optimize hot water expenditure. It has several modes to facilitate its use.

388 £ on Amazon
Buying guide • November 2023

Best flat water heater

Any specific needs?

The best flat water heater in 2021

The best entry-level flat water heater

The best high-end flat water heater

The best alternative for the family

Your guide : Samuel

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Comparison table of the best flat water heaters

Ariston Velis Evo - 50 L 5
Thermex IF Smart - 80 L 6
Atlantic Linéo - 80 L 7
Thermor Malicio 2 - 80 L 8
Ariston Velis Evo - 50 L
Thermex IF Smart - 80 L
Atlantic Linéo - 80 L
Thermor Malicio 2 - 80 L
With its 50 L capacity, this Ariston warmer is ideal for those who don't have much room. It combines several technologies that allow you to control the volume of water used.
With its compact size, this water heater adapts perfectly to all types of use. Offering a decent performance, it is ideal for small budgets that want to have hot water available all day long.
This flat semi-accumulation water heater has all the technologies in terms of heating. Space-saving and economical, it can operate permanently and can be controlled remotely.
Sleek design and fully functional, Thermor Malicio 2 has a connected function to optimize hot water expenditure. It has several modes to facilitate its use.
Energy class
50 L
80 L
80 L
80 L
Eco Evo - Nanomix Function - Shower Ready
Remote control with the Cozytouch app
Remote control with the Cozytouch app
Heating time
1h30 min
1h45 min
4h04 min
4h04 min

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Buying guide - flat water heater

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How to choose your flat water heater

Having a water heater at home provides comfort and well-being, especially in cold weather. But these appliances can quickly turn into a real money pit if you choose them randomly. Here are some criteria to consider if you want to find a good quality flat water heater.

#1 - The capacity

The capacity of an instantaneous water heater varies from 50 to 200 L. Those with a smaller capacity are suitable for one person's hot water needs, while those with a larger tank are suitable for families of more than 4 people. Don't forget about other machines that need hot water, such as washing machines, when making the calculation. This allows you to find the water heater that covers all your hot water needs.

#2 - The power

The more powerful your appliance, the more energy it consumes. In the case of a flat water heater, you should always consider the number of users in a household to determine the power of the unit you should buy. For example, you should get a machine with a power rating of 3.7 kW if you use a hand-washer and up to 11 kW if you need running hot water for your baths.

#3 - The installation

Although a flat water heater requires little space for installation, it is useful to determine how it will be positioned; on this will also depend its performance. You may want to choose a vertically mounted unit to optimize use and quickly access the digital console. If you have a lot of space, a flat horizontal water heater is recommended to avoid leaving a gap on the sides. But there are also connected models that can be installed as you wish. The trick is to know how to harmonize the appliance with the rest of the decoration.

#4 - The modes

A flat water heater should offer the basic energy-saving operating modes. Without this, the appliance will not be cost effective and you may even find it difficult to use. Thus, make sure that the three modes are present: manual, automatic and absence.

#5 - The options

This is certainly not a fundamental criterion for those who are just looking to have hot water in their home. But it is still useful to include it among the elements to consider when choosing a water heater pleases. This greatly improves the comfort of use and handling of the machine. For example, you should check if there is an off-peak program, smart mode or boost mode to heat water quickly.

How to maintain a flat water heater?

A machine of any kind always needs a minimum of maintenance. This will both extend its life and keep it in excellent condition, even after years of use. Follow these tips if you want your flat water heater to stay in top shape.

The safety group: This element should be checked regularly. For example, you can take about 10 minutes a month to do a simple check. This consists of checking the valve to eliminate deposits that could prevent it from working properly.

Draining: It is highly recommended to drain the water periodically, especially if your flat water heater is not connected to an electrical power source for a long period of time.

Tank: As a key component of a water heater, the tank should be well maintained. This means replacing the anode if it is too worn, or is less than 10 mm in diameter. Cleaning the tank is more difficult and it is better to delegate the task to a professional to avoid any malfunction. Also, you should always make sure to turn on your water heater when you are away or on vacation. Otherwise, you risk damaging the entire system as the water heats up continuously when not in use.

The different types of flat water heaters

There are 4 main types of flat water heaters. Each has its own operation and technology used in its design. The electrical resistance is also a crucial element that differentiates them.

The armoured water heater

It is a type of flat water heater that resists all external elements that could damage it, such as wind corrosion or the effects of time. Often designed with high quality materials, it is characterized by its thermoplastic resistance completely embedded in the water. This also allows the water to heat up more quickly. It is especially suitable for those with a limited budget.

The disadvantage of this type of appliance is its sensitivity to hard water, which will logically lead to corrosion. The models are also more difficult to maintain due to the complexity of the protection system.

The flat soapstone water heater

This type of water heater is equipped with a resistance made from soapstone which is a rock with a great resistance to the effects of limestone contained in water. The appliance is also protected by an enamel sleeve that prevents water from reaching the resistance. Some models are even equipped with a magnesium anode to fight against corrosion. This helps to optimize the life of the machine. The flat soapstone water heater is therefore highly recommended for those who live in areas where the water is very hard.

It is also an easy to maintain device, because you will not need to drain the water to replace the resistance. This type of water heater has an excellent resistance to corrosion due to the ACI or impressed current anode system. Generally composed of an electronic device and a titanium electrode, it effectively protects the tank from rust and other wear. The magnesium that covers the entire water heater resists any external attack.

Another advantage is the possibility of installing a more effective protection system by combining the integrated one with hybrid anodes. This ensures a long service life and also optimizes the maintenance of the machine. But you should definitely not overheat the machine to avoid any malfunction.

The impressed current water heater

This water heater is a real technological gem as it combines the ACI system and the anode to strengthen the protection of the machine. This means the tank can be used for many years without suffering the effects of time. No matter what the quality of the water and its hardness, the water heater remains efficient. Therefore, it does not need any particular maintenance. It is distinguished by the efficiency of its insulation and its precise thermostat.

It is the ideal device for intensive use, because not only is it resistant, but it also heats water quickly. Moreover, you can adjust the temperature as you wish. This type of water heater has only advantages and you will be amply satisfied with its performance.

The HPC water heater

Flat or conventional water heater?

Flat water heater

The advantage of a flat water heater lies above all in its reduced dimensions. As its name suggests, it is an appliance with an ultra-thin design that blends in perfectly with all types of space. It also guarantees a much faster heating time and is very easy to use and install.

But its shape can sometimes turn into a handicap. Indeed, a flat water heater has a much lower hot water storage capacity than a standard model. The price is also a real disadvantage as you have to spend more, no matter which range you choose.

Classic water heater

The classic water heater is a model that is perfectly suited for family use because of its tank that can hold a large volume of hot water, and you are spoilt for choice when it comes to purchasing. If you are on a budget or don't want to spend too much money, this type of heater is just what you need.

The main drawback is the heating time. A conventional water heater takes time to reach the right temperature to provide hot water quickly. As a result, it uses more energy, despite the fact that you can use it during off-peak hours. You also need to perform more frequent maintenance if you want the tank to work properly.


If you have a large family or don't want to break the bank, consider a conventional water heater. On the other hand, a flat water heater is more expensive, but it allows you to reduce your electricity and water bills. Also, with this type of heater, you won't have to worry too much about where you're going to install it.

Why buy a flat water heater?

Space saving

A flat water heater saves space, especially if you have a small living space. It is more compact than other types of appliances and because it is so light and has a depth of 31 to 51 cm, it can be installed on any wall. In addition, the smaller models can be placed horizontally or vertically, depending on the layout of your furniture and decoration. Basically, it is a very discreet device that can be used in all types of homes.

Energy saving

Unlike standard water heaters that have a more modest heating performance, a flat model heats water almost instantly. If you live alone, a 40L unit is more than enough to meet all your hot water needs. Flat water heaters with a capacity of 65 L to 120 L are more suitable for family use. As a general rule, these types of water heaters can operate during peak hours without affecting your electricity bill too much. If you have an urgent need, the boost function allows you to heat the water more quickly.


The most advanced flat water heater models have a connected feature so you can control it remotely. This means you can use your smartphone or tablet to fully control your water heater. It's also a smart device because of its ability to calculate the needs of each household and adjust consumption based on that parameter.


A flat water heater is more aesthetically pleasing than conventional models. Its sleek design and sober colour will blend in perfectly with your decor. While a water heater is usually installed in the kitchen or bathroom, the flat water heater can be installed in any room of the house.

Easy to install

A flat water heater is both compact and easy to install. In fact, you won't need any outside help to install it. As for the connection, all you have to do is follow the user's manual to connect the pipes and ducts.

The best brands of flat water heaters

In our opinion, the best brands of flat water heaters in 2022 are :

De Dietrich

Created in 1968, this French brand is well known in the field. Its heating systems are known for their high performance anti-corrosion devices. In addition to its flat water heaters, it also offers electric and solar water heaters, not to mention connected water heaters.

An Italian company founded in the 1960s, Ariston is one of the pioneers in terms of heating systems. Its electric water heaters are of excellent quality, but it has made a name for itself with its innovative connected devices for perfect control of energy costs.

You really can't do without this brand! De Dietrich is a French brand that has been in the business for a hundred years and has always focused on consumer satisfaction by offering very affordable appliances with unmatched performance. It uses different technologies to design its flat water heaters as well as other ultra-resistant models.

Created in the 1930s, this brand is among the best on the market. It is known for its long-lasting soapstone water heaters. It offers users compact appliances, but also large capacity water heaters for the whole family.

A subsidiary of the famous Ariston brand, it is famous for its economical water heaters equipped with the latest technology. Its dedicated ChaffoLink technology, which allows total control of energy costs, is a huge success. It offers a wide range of solutions to suit all budgets.

What is the price for a flat water heater

The diagram below will help you to get an idea of the typical prices for each price range (entry-level, mid-range and high-end).

However, more expensive does not necessarily mean better.

We therefore advise you to always consult our ranking before deciding, rather than blindly relying on price ranges.

200 £ to 300 £
300 £ to 500 £
more than 500 £
Price range diagram


Choose a programmable and intelligent water heater

Opting for a programmable model allows for significant energy savings. You can control the amount of water that corresponds to your needs. This type of water heater will then memorize the parameters you have entered and adjust your consumption accordingly.

Choose the right capacity

Although a flat water heater is energy efficient, it is essential to choose the right capacity for the number of people living under the same roof. If you are alone, don't make the mistake of buying a 200L unit, unless your guests also use your hot water. On the other hand, if you are a large family, avoid using a 40 L water heater, as it is just enough for one person.

Do not overheat the water

If you happen to leave your water heater running all day long, now is the time to change your habits. You need to set the thermostat properly so that the temperature does not exceed 60°C. Not only will this reduce your bills, but the unit will maintain good performance.

If there is no space for draining the water...

All you have to do is take a small hose and connect it to the drain valve that is on the bottom of the tank. The hose should be long enough to reach a place to dump the drained water, such as a bathtub or shower.

Turn off the electricity and water supply before cleaning

This makes it easy to do the cleaning and also avoids any mishaps, especially for the power that can cause a short circuit. Basically, you should never proceed with maintenance without checking that the machine is unplugged and that water is no longer coming into the tank.


How does a flat water heater work?

In general, the flat water heater works like a conventional water heater. The only difference is that it can heat throughout the day thanks to a continuous charging system for tank refueling. Don't hesitate to apply the few tips we have recommended.

Can I use a softener in my water heater?

You can perfectly well use a water softener to make the water in the tank less hard. But ideally you should not use one, as excessively soft water could damage the tank. It is also a way to preserve your machine from premature corrosion and also tomaintain your flatwater heater properly.

Which electrical connection for my water heater?

The electrical installation of such an appliance must follow the NF-C156-100 standard. Thus, you must imperatively connect it to the ground. If the cable is not supplied, the use of a rigid wire of at least 2.5 mm section is mandatory to avoid any incident such as overheating. You will find the essentials to know in this guide.

Can I install the flat water heater in my living room?

Yes, a flat water heater, because of its design, is a decorative element in its own right. This is also one of the reasons to buy this type of water heater, even if you prefer to install it in the kitchen or bathroom for more discretion.


Note: Below are some of the sources we have consulted in writing this article. Links to other sites are not continuously updated. It is therefore possible that a link may not be found. Please use a search engine to find the desired information.
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March 2022 : Translation of this buying guide from our partner

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Our selection
Ariston Velis Evo - 50 L 9
Ariston Velis Evo - 50 L
Thermex IF Smart - 80 L 10
Thermex IF Smart - 80 L
Atlantic Linéo - 80 L 11
Atlantic Linéo - 80 L
Thermor Malicio 2 - 80 L 12
Thermor Malicio 2 - 80 L


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