Last updated: August 8, 2021

Here we present all the condensing boilers we have tested in detail. We have compiled detailed background information and added a summary of customer reviews on the internet.

In this way, we would like to make your purchase decision easier and help you find the best condensing boiler for you.

You will also find answers to frequently asked questions in our guide. If available, we also offer interesting test videos. Furthermore, you will also find some important information on this page that you should definitely pay attention to if you want to buy a condensing boiler.


  • Condensing boilers are on average 15 percent more energy efficient than standard boilers. They are also safer, as the risk of carbon monoxide poisoning is significantly reduced.
  • Condensing boilers also have the advantage of low energy loss, which saves on heating costs. Most models are also very space-saving.
  • In general, a distinction can be made between condensing boilers that function as instantaneous water heaters and condensing boilers with hot water storage tanks. Depending on your hot water consumption, one or the other system will suit you better.

The Best Condensing Boiler: Our Choices

Guide: Questions you should ask yourself before buying a condensing boiler

What is a condensing boiler?

A condensing boiler is a wall-mounted hot water heating system that ideally uses the energy content of natural gas almost completely. If you use a condensing boiler, you can save energy and thus CO² emissions.

Condensing boilers are on average 15% more energy efficient than standard boilers. They are also safer, as the risk of carbon monoxide poisoning is significantly reduced. (Image source: / horjaraul)

A condensing boiler is a gas boiler and is basically a further development of the low-temperature boiler. Therefore, the condensing boiler is the first choice when deciding on a new heating system that can be installed in the home.

In a condensing boiler, the heating water is heated via combustion heat. However, the heat contained in the flue gas does not escape unused via the chimney, but is used by the condensing boiler.

The water vapour contained in the flue gases is cooled down to 57° C with the help of special heat exchangers. The water vapour condenses and the condensation heat is released.

To give you a better idea of how a condensing boiler works, we have selected a video in which condensing technology is explained briefly and clearly:

What does a condensing boiler consume?

The energy consumption of condensing boilers is lower than that of other systems. Compared to low-temperature boilers, the savings with a condensing boiler are at least 10 percent.

Condensing boilers are on average 15 percent more energy efficient than standard boilers. They are also safer, as the risk of carbon monoxide poisoning is significantly reduced.

With even older standard boilers, the savings potential is even higher. Here, fuel costs can be saved by up to 30 percent.

What legal regulations do I need to be aware of when buying a condensing boiler?

Before buying a condensing boiler, you should familiarise yourself with the EU's new Ecodesign Directive. This ensures that products are as environmentally friendly as possible, both in their manufacture and in their use.

Since 26 September 2015, a detailed regulation has been in force in this regard (EU Regulation No. 813/2013), which requires that broken boilers may only be replaced by energy-efficient condensing boilers. The sale of conventional heating boilers to wholesalers or installation companies has been prohibited since then.

Did you know that in the case of a rented flat, the landlord bears the costs for the replacement of a condensing boiler?

The tenant himself only has to pay for regular maintenance.

If a boiler is broken, it should be replaced with a new condensing boiler. However, if conventional devices are still in stock at plumbers or DIY stores, you can still opt for them.

What does a condensing boiler cost?

Condensing boilers are offered in various output classes, efficiency classes and brands. Depending on whether the boiler is supplied with a storage tank, installation aids and heating control, the costs vary.

Condensing boilers require a larger heat exchanger surface or radiator than conventional boilers. This makes them somewhat more expensive to purchase. Existing chimneys must also be adapted to this type of boiler. As a rule, a metal pipe is inserted into the chimney, which incurs additional costs.

The price range for condensing boilers is between 2,000 and 8,000 euros. The manufacturer and the technology used determine how much a condensing boiler costs.

However, the higher purchase costs pay for themselves after just a few years, as a condensing boiler can save 10 to 20 percent on heating costs.

Type Price range
Condensing boiler € 2,000 - € 8,000
Water storage tank € 800 to € 1,500
Installation and commissioning approx. € 300

Find out whether government subsidies are available in your case. This way you can save additional costs. Popular subsidies are those from the Kreditanstalt für Wiederaufbau (kfW) and the Federal Office of Economics and Export Control (BAFA).

Basically, the more environmentally friendly the heating system, the higher the subsidies.

What alternatives are there to condensing boilers?

There are many alternatives to condensing boilers. If it is an old building, converting to a condensing boiler is often only possible at great expense. Therefore, we have prepared a clear table with the individual alternatives to condensing boilers.

Alternative Description
Boiler boilers Boiler boilers are wall-mounted heating centres. They are heating boilers with an integrated hot water tank (usually 30 - 45 litres capacity).
Combi boiler Like the condensing boiler, the combi boiler is a gas boiler that produces hot water as well as heating. This alternative is usually more space-saving and energy-efficient than using two separate appliances. In terms of energy efficiency, however, condensing boilers are state of the art.
Calorific value boilers Calorific value boilers are the classic gas boilers, so-called atmospheric calorific value boilers. They are only used for heating purposes and cannot provide hot water directly - like a combi boiler. If an old building would require too extensive conversion work for a condensing boiler, the calorific value boiler is preferable.
Pellet heating A pellet heating system works like a conventional gas heating system. The fuel is burned and the heat is released via the heating circuit. The difference to the gas boiler is that the fuel must be provided in an additional store.
Heat pump The heat pump takes its energy from the ground or the ambient air. Compared to pellet heating, the fuel costs are higher, but there is no need for a dedicated storage room. The heat pump runs on electricity.

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

Condensing boilers offer many advantages. However, we don't want to deprive you of the disadvantages. The low energy loss and the resulting heating cost savings are offset by the constantly rising gas prices.

  • Low energy loss - heating cost savings
  • Space-saving design
  • Low consumption
  • Environmentally friendly
  • In apartment buildings it is easier to see who consumes how much
  • Only low heat output possible
  • Requires space in kitchen or bathroom
  • Gas prices rise

In general, however, a distinction can be made between condensing boilers that function as instantaneous water heaters and condensing boilers with hot water storage tanks. Depending on your hot water consumption, one or the other system will suit you better.

  • Condensing boiler with instantaneous water heater
  • Condensing boiler with hot water cylinder

Here we are only concerned with providing hot water for showering, washing and drinking. In a condensing boiler, the heat for heating is heated in a continuous flow system anyway.

What distinguishes a condensing boiler with an instantaneous water heater and what are its advantages and disadvantages?

The instantaneous water heater provides hot water in the household. But unlike a condensing boiler with a storage tank, no water is heated in advance here. The boiler only starts working when the tap is turned on and then immediately heats the required water.

An instantaneous water heater is suitable for heating water in low quantities. Because there is no water storage tank, this variant also requires less space. Installation is relatively easy.

  • Small space requirement
  • Lower investment costs
  • Relatively simple installation
  • Unsuitable for high hot water demand
  • Hot water must be heated only when needed

What are the features of a condensing boiler with hot water cylinder and what are its advantages and disadvantages?

Condensing boilers with hot water storage heat the water in advance and store it until it is needed. A hot water cylinder is particularly suitable for higher hot water requirements.

A hot water cylinder is recommended, for example, in a multi-family house where more hot water is needed daily for showering, washing, etc. A hot water tank can also be used to supply several taps at the same time with a higher draw-off quantity.

  • Suitable for higher hot water demand
  • hot water is always available
  • More expensive investment costs
  • somewhat more complex installation

Purchase criteria: You can use these factors to compare and evaluate condensing boilers

In the following, we show you which aspects you can use to decide between the different models of condensing boilers.
The criteria you can use to compare condensing boilers include:

  • Calorific value
  • Condensing value
  • Efficiency
  • Room air dependent or independent
  • With solar collectors

We will now go into more detail on the individual purchase criteria.

Calorific value

The so-called calorific value (Hi) or energy content is given in kilowatt hours per cubic metre (kWh/m³). It indicates the amount of heat that can be used during combustion without condensation occurring. The calorific value for natural gas is approximately 9 to 10.4 kWh/m³.

Calorific value

The calorific value (Hs) also includes the amount of heat of the water vapour made usable by condensation. On average, the calorific value is therefore 10 percent higher than the heating value and is between 9.5 and 11.5 kWh/m³ for gas condensing boilers, depending on the quality.


The efficiency is the difference between the calorific value and the calorific value. Since the calorific value is higher than the heating value, the efficiency is often over 100 percent. This is because the efficiency is still related to the calorific value.

A heating system that has an efficiency of 100 % only achieves about 90 % when referred to the calorific value. With optimum utilisation of the calorific value, efficiency values of up to 111 % can be achieved.

Room-air dependent or independent

When operating gas heaters, a distinction is made between room-air-dependent and room-air-independent operation. Regardless of the type of heating, oxygen is always required for combustion.

In the past, the oxygen was taken from the room air. With this room-air-dependent operation, therefore, a supply of air must always be provided. Therefore, there are regulations on how the room in which the heater is located can be reliably supplied with combustion air.

In room-air-independent operation, combustion air is supplied via a pipe. In gas condensing boilers, the flue pipes consist of a double-shell pipe-in-pipe. The combustion air is supplied in the outer shell and the flue gases are discharged in the inner pipe.

In room-air-independent operation, no special requirements are placed on the installation of the gas condensing boiler. Room-air-independent operation is also more economical, as combustion is optimised.

With solar collectors

If you want to heat in a particularly environmentally friendly way, you can also integrate solar thermal energy into your gas condensing boiler. However, a solar thermal system does not always make sense. A suitable roof surface must be available, with the right compass direction and roof pitch.

Solar collectors can also save gas and thus heating costs. (Image source: / Ulleo)

All well-known German manufacturers now offer complete systems, i.e. condensing boiler, solar system and corresponding solar control as well as suitable storage tanks. These components must be installed additionally.

The additional costs for combining a condensing boiler with solar thermal are very high. You should expect costs between 6,000 and 12,000 euros. However, subsidies of 90 euros per square metre can be deducted again.

Using solar collectors can save a lot of gas. In summer and also in the transitional period, the condensing boiler itself hardly needs to start.

In new buildings, it is definitely worth combining the condensing boiler with a solar system. This also complies with the regulations of the legislator, which stipulates the use of renewable energies in the Renewable Energies Heat Act.

Facts worth knowing about condensing boilers

What do I have to consider when installing a condensing boiler?

In order to be able to start up your new condensing boiler properly, a few prerequisites must be met:

  • An acid-proof hose must be fitted in the chimney so that it is not damaged by the low flue gas temperatures.
  • A drain for the condensation water must be placed under the boiler.

What happens to the condensate produced by the condensing boiler?

The condensate produced by a condensing boiler is acidic, it has a pH content of around 4. However, since gas condensing boilers do not produce very much condensate, it can be disposed of via the waste water pipe. This applies without restriction to gas heating systems up to an output of 25 kilowatts.

There are special regulations for larger boilers. Here it is possible that a neutralisation system is required. More detailed information on this can be obtained from a heating specialist.

Do I need new radiators when modernising with a condensing gas heating system?

This question, whether you also need new radiators when you convert to an economical condensing boiler, comes up again and again. However, this is only necessary in very few cases.

The condensing boiler works particularly economically with low flow temperatures. But the advantage of using the condensation heat can also be used at higher flow temperatures. This is the reason why radiators are only replaced in the rarest of cases.

The savings effect is merely not quite as great as with panel heating systems that manage with low flow temperatures.

Does the chimney sweep still come when a condensing boiler is used?

With conventional gas heating systems, the chimney sweep comes once a year. With condensing boilers, the chimney sweep comes twice every six years for a so-called fireplace inspection.

In the case of room sealed gas heating systems, the chimney sweep comes every two years for a safety check. If the condensing boiler has a so-called self-calibrating control system, he only comes every three years.

The chimney sweep also visits gas condensing boilers, but less frequently. (Image source: / Kakaket)

Room-air dependent heating systems are still inspected once a year. Emission measurements according to BlmSchV and cleaning of the flue pipe are no longer necessary with condensing boilers.

Does a condensing boiler need to be serviced?

A gas condensing boiler should definitely be serviced regularly. Gas is a highly explosive fuel, which is why maintenance is absolutely recommended.

During maintenance, the heating engineer checks the tightness of the gas pipes and all connections. The burner is cleaned, the heat exchangers checked and the water pressure adjusted. The control system is also checked in order to comply with the prescribed emission limits.

Image source: / 37777189

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