Thermodynamic water heaters in Luxembourg: the guide
Why is this type of water heater so popular? Should you buy one in 2026? We explain everything in this guide.
Key points to remember
- The thermodynamic water heater works like a heat pump by capturing heat from the air to heat water
- It can reduce your hot water bill by up to 70%.
- There are two main types: on room air (requiring an unheated room of at least 20m³) and on outside air (ideal for small homes).
What is a thermodynamic water heater?
A thermodynamic water heater (CET) is an appliance designed to produce domestic hot water by combining two technologies: a heat pump and a storage tank.
In practical terms, this system works on the principle of aerothermy: in other words, it generates energy from the air. It captures the heat naturally present in the air to heat the water, reducing your hot water bill by 70%. It works in exactly the same way as a heat pump classic.
In contrast, an electric water heater will have to use a resistance and consume energy that is not naturally present to heat the water.
The components of a thermodynamic water heater
First of all, here are the various technical components that enable the water heater to operate:
- A fan which draws in ambient air
- A evaporatorwhich contains a refrigerant that captures heat from the air
- A compressor which increases the pressure and temperature of the fluid
- A condenser which transfers the heat from the fluid to the water in the tank
- A auxiliary electric heater which takes over if necessary (if there is not enough energy to heat the water properly)
- A storage tank (or tank) which holds the hot water until it is used
And here is the process that takes place in a thermodynamic model:
- The fan draws in ambient or outside air containing calories (even in cold weather)
- This air transfers its heat to the refrigerant in the evaporator
- The fluid turns into a gas then passes through the compressor where its temperature rises
- The condenser transfers the heat from the fluid to the water in the tank.
- The cooled fluid returns to the liquid state and the cycle starts again.
- ...And so on, for more than 20 years! (average lifespan of a thermodynamic hot water tank)
Thanks to this process, thermodynamic water heaters consume around 3 times less electricity than traditional electric water heaters to produce the same amount of hot water.
Sound coefficient of performance (COP) is generally between 3 and 4, which means that it produces 3 to 4 kWh of heat for just 1 kWh of electricity consumed. This is the same coefficient as that of traditional heat pumps for heating.
The different types of thermodynamic water heaters
You will have realised that thermodynamic water heaters need to draw energy from the air. There are two main types of system: those that draw their energy from the air in the room, and those that draw their energy from the outside air.
Thermodynamic water heaters using ambient air
This model captures heat from the air in the room where it is installed. It is very easy to install, and is ideally placed in an unheated space such as a garage, utility room or cellar. However, please note that :
- The room must have a minimum volume of 20 m³. (you need enough air for the machine to work)
- The room temperature should remain between 5°C and 35°C throughout the year. (so as not to disrupt its operation)
- This system will tend to cool the room in which it is installed. (So don't install the water heater in a room that you plan to make habitable or heat later).
Outdoor air-source thermodynamic water heater
This model extracts heat directly from the outside air. It is available in two versions:
- Monobloc version The appliance is installed indoors and connected to the outside by air ducts.
- Split version The heat pump is installed outside, while the storage tank is inside.
It's perfect for situations where the home is small: there will always be enough supply air. However, be careful to comply with regulations if you are installing the heat pump outside. A certain noise level must be respected at the property boundary (see the guide to heat pumps in Luxembourg).
Finally, note that there is also an extracted air variant: the thermodynamic water heater draws energy from the air extracted by the home's CMV system. This can be useful if your home is already ventilated, but requires very fine-tuning to ensure that the heater does not overheat.
The advantages of a thermodynamic water heater in Luxembourg
Installing a thermodynamic water heater in Luxembourg has many advantages, both economically and ecologically. But there are also a few drawbacks. Here's everything you need to know if you're on the fence about this method of producing domestic hot water:
The benefits
- You consume very little energy: you'll reduce your hot water bill by 70%. Even more if you also install a heat pump for your heating.
- You benefit from a very short heat-up time (hot water is available quickly) and the equipment lasts longer than average (20 years compared with 10-15 years for electric water heaters).
- You are eligible for renovation grants (Klimabonus, Enoprimes...). See the 2026 scale.
- You increase the value of your property (by improving your energy passport)
- Some models are compatible with photovoltaic panels (so you can use your own electricity to heat your water)
Disadvantages
- The initial cost (equipment and installation) is 2 to 4 times higher than an electric or thermal water heater (generally between €6,000 and €9,000, depending on the size and specific features of the project).
- This type of water heater is difficult to install in condominiums (unless you opt for a collective model)
- You need an unheated room with sufficient air volumeor ducts drawing air from outside (which adds extra to the installation bill).
- There may be some noise pollution: the fan and compressor can emit 30 to 45 decibels depending on the model
- If the heat pump is installed outdoors, the regulations on noise levels at property boundaries must be complied with.
Price and profitability of a thermodynamic water heater in Luxembourg
One of the most important aspects to consider before investing in a thermodynamic water heater is its cost and long-term profitability. In Luxembourg, a number of specific factors influence these parameters and deserve particular attention.
How much does a thermodynamic water heater cost in Luxembourg?
The price of a thermodynamic water heater in Luxembourg varies according to a number of criteria: the brand, the capacity, the type of system and the options available.
Here is an average of the unsubsidised prices observed in 2026 (including installation):
| Type of system | Capacity | Price including installation |
|---|---|---|
| On ambient air | 200-300L | 5 700 - 7 500 € |
| On outside air (monobloc) | 200-300L | 6 100 - 8 500 € |
| On outside air (split) | 200-300L | 6 800 - 10 800 € |
Note that the Luxembourg government's renovation grants help to finance a large proportion of this work.
On average, it is estimated that the return on investment for a thermodynamic water heater in Luxembourg is between 4 and 7 yearswhich is very attractive given its lifespan of 15 to 20 years.
Factors influencing price
In Luxembourg, as elsewhere, the price of a thermodynamic water heater varies according to a number of criteria:
- Balloon capacity The capacity: this generally varies between 150 and 300 litres, depending on the number of people in the household (150L for 2 people, and 300L for 4 people in general).
- The technology used Split models are generally more expensive than monoblocks, as they require 2 separate units to be installed in two different locations.
- The brand and performance The major brands such as Atlantic, Thermor, Saunier Duval and Ariston offer different ranges with varying levels of performance (it's up to you to decide whether you prefer a budget or top-of-the-range model).
- Additional features : Some models offer advanced functions such as an anti-scale mode, control connected to your home automation system, learning your habits, and so on. But these features come at a price.
How do I choose the right thermodynamic water heater in Luxembourg?
The ideal thermodynamic water heater for you will depend mainly on the configuration of your house or flat. This is particularly the case in Luxembourg, where there is a wide variety of housing types (terraced houses, blocks of flats, detached houses on large plots of land, etc.).
Here is a table to help you determine the best model for your situation:
| Type of thermodynamic water heater | Ideal for... | Points of attention |
|---|---|---|
| On ambient air | Houses with garage, basement or spacious utility room | - Minimum volume of 20 m³ required - Room cooling |
| On outside air (monobloc) | Flats or houses with limited space | - Requires co-ownership authorisation - Ventilation ducts to be provided |
| On outside air (split) | Flats or houses with no space to install ducts | - Requires co-ownership authorisation for outdoor unit - More complex installation - Better performance in cold weather |
| On extracted air (VMC) | New homes or complete renovation with VMC | - Requires a compatible CMV - Ideal for new, well-insulated buildings - Saving space |
A word of advice to Luxembourg: if you can, Choose outdoor air models, which offer better performance in cold weather.
Finally, to find the best model of thermodynamic water heater, carefully analyse :
- Coefficient of performance (COP) The higher the COP, the more efficient the appliance. Look for a COP of at least 3.
- Operating temperature range : Opt for a model capable of operating efficiently between -5°C and 35°C.
- Noise level : Choose recent models with quiet operation (noise level below 40 dB). Especially if you live in a flat!
- The type of electrical resistance The steatite element is more resistant to limescale, especially in Luxembourg where the water is very hard.
- Anti-corrosion protection devices Opt for systems with ACI (impressed current anode) or ACI Hybrid technology - they offer greater durability over time.
Finally, choose a popular brand that is well known on the European market. Brands such as Atlantic, Thermor, Ariston, Saunier Duval, Daikin and Viessmann offer high-performance models at a range of prices. You should also pay attention to the warranties offered by the various manufacturers.
Finally, if you've made up your mind: call on one of our partner installers. We'll give you a free quote for your project.
FAQ : Frequently asked questions about thermodynamic water heaters
What is a thermodynamic water heater and how does it work?
A thermodynamic water heater is an appliance that combines a heat pump and a storage tank to produce domestic hot water. This system can reduce your hot water bill by up to 70% compared with a traditional electric water heater.
What are the different types of thermodynamic water heater available?
There are two main types of thermodynamic water heaters: room air heaters, which capture heat from the air in the room where they are installed, and outdoor air heaters, which extract heat directly from the outside air.
How efficient is a thermodynamic water heater?
The coefficient of performance (COP) of a thermodynamic water heater is generally between 3 and 4. This means that it produces 3 to 4 kWh of heat for just 1 kWh of electricity consumed, making this system three times more efficient than a traditional electric water heater.
How much does a thermodynamic water heater cost in Luxembourg?
In Luxembourg, the price of a thermodynamic water heater (excluding subsidies) varies according to type and capacity, ranging from €5,700 to €7,500 for an ambient air model, €6,100 to €8,500 for a monobloc outdoor air model, and €6,800 to €10,800 for a split model (including installation).
What are the disadvantages of a thermodynamic water heater?
The main disadvantage of a thermodynamic water heater is its high purchase and installation price, which is 2 to 4 times higher than that of a conventional electric water heater. Installation can be complex, requiring an unheated room of at least 20 m³ or ducts drawing in outside air. The system can also generate noise nuisance (between 30 and 45 decibels), and installing it in a condominium can be complicated, often requiring specific authorisations.
Can a thermodynamic water heater be installed in a small flat?
Yes, it is possible to install a thermodynamic water heater in a small flat by opting for an outdoor air model. The monobloc version requires air ducts to the outside, while the split version places the heat pump outside and only the tank inside.
How long does a thermodynamic water heater last?
The average lifespan of a thermodynamic water heater is around 20 years.This is longer than the 10-15 years generally observed for traditional electric water heaters.
Does a thermodynamic water heater work in cold weather?
Yes, because it is capable of extracting heat from the air, even at low temperatures. For cold climates such as Luxembourg, we recommend choosing a model designed to operate effectively in sub-zero temperatures, ideally down to -5°C or less.