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Gas heating – reliable and flexible to use

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Whether for a new build or a modernisation project, Viessmann offers gas heating systems, gas boilers and gas hybrid heating systems for owner-occupied apartments, detached houses and major housing developments. Use of the latest technologies ensures a wide range of needs can be met whilst also offering convenient heating with either natural gas or LPG.

Compact, versatile and efficient

Viessmann gas heating systems are noted for their extremely compact design and highly efficient operation utilising condensing technology. It is no accident that gas heating is the most commonly installed heating system in Germany in detached homes, two-family houses and apartment buildings (accounting for 49.3  percent of systems) and in apartments (48.2  percent). This means that just under half of all heat generators in use here run on natural gas, according to the results of the study "Wie heizt Deutschland 2019?" [German Heating System Survey 2019] conducted by the Federal Association for Energy and Water Management (BDEW).  

Owners of detached homes, two-family houses and small apartment buildings in particular benefit from the wide portfolio of products that Viessmann offers in the residential buildings sector. Regardless of whether they opt for a compact condensing appliance in the form of a wall mounted gas boiler or a floorstanding gas boiler with solar indirect coil: with rated heating outputs of up to 80  kW, Viessmann gas heating systems can meet heating and heat demands efficiently and reliably at all times.

Detailed information on gas condensing boilers is provided in the section on gas heating with condensing technology. Anyone interested in the proven conventional heating technology for the 405 to 2000  kW output range will find all the important information in the section on low temperature gas boilers.

Caring for the environment with condensing technology

All Viessmann gas heating systems meet EU-wide requirements for efficient condensing technology. Up to 98  percent of the energy used is converted into heat. With such unbeatably high levels of efficiency, everyone who uses a gas condensing boiler is making a positive contribution to protecting the climate and the environment. By comparison, most heating systems without condensing technology, for example low temperature gas boilers, manage about 87  percent under the same conditions. Innovative technology, such as the new gas adsorption heating appliance, reduces gas consumption by around 25  percent compared to conventional condensing technology. This saves fuel, reduces emissions still further and makes heating with a gas boiler even more efficient.

High efficiency

Viessmann gas boilers with condensing technology convert up to 98  percent of the energy used into heat. How this works in detail and which components play a role is explained in the section on the function and benefits of gas condensing technology.

Diagram: How a gas condensing boiler works

Buying tips and requirements

The operation of a gas heating system requires certain conditions to be met. Once these are satisfied, consistently economical operation is ensured. Find out here about these requirements and what should be borne in mind before buying.

Which gas heating system is best for me?

Before homeowners buy a gas heating system, it is advisable to get an overview of the variety of models available and the benefits they offer. In principle, condensing boilers are now considered state of the art and are therefore very reliable. If homeowners have only a low heat demand, they can usually opt for a very compact wall mounted appliance that can theoretically even fit into a wall cupboard. Combi boilers with a built-in loading cylinder, which ensure constant high levels of DHW convenience, are somewhat wider. If homeowners plan to use solar energy from the outset, gas condensing boilers with an integral solar loading cylinder are the best choice.

In the case of large buildings and industrial plants, gas boilers in the higher output range are worth considering. They optionally use condensing technology and, thanks to cascade functions, can achieve rated heating outputs of up to 2000 kW.

An expert consultation is the first step in any heating system modernisation project

For a new gas heating system to be cost-saving and reliable in the long term, it must match the heat demand. This is best determined with the help of a professional.  

Buying a gas heating system with subsidies

Homeowners opting for a gas heating system should also consider using renewable energies. This is because the combination of a gas condensing boiler with a solar thermal system, heat pump or wood heating is subsidised by the state with very attractive grants. In fact, the Federal Office for Economic Affairs and Export Control (BAFA) covers up to 30  percent of the eligible costs for gas hybrid heating systems through the Federal Funding for Energy-Efficient Buildings (BEG). If the gas heating system is prepared for the future integration of renewable energies, the subsidy rate is up to 25  percent. Detailed information on this topic can also be found in the section on subsidies for gas condensing technology.

Vitodens 343-F – gas condensing storage combi boiler with integral 170 litre stainless steel DHW cylinder with solar indirect coil.

Requirements for operating a gas condensing heating system

Those wishing to buy a gas heating system also need to decide in advance on the technology. Conventional boilers can now only be used in exceptional cases in the housing industry. Gas heating systems utilising condensing technology are considered state of the art. These are noted for their high efficiency, as they can convert almost all of a fuel's energy content into heat. To find out more about what this technology entails, take a look at the section on how gas condensing boilers work. To operate a gas condensing heating system, however, some requirements need to be met.

One of the benefits of gas heating is that system owners do not have to store the fuel. Natural gas is usually supplied directly from the gas connection valve, thereby ensuring an exceptionally high degree of operating convenience. Or at least that's how it is in most cases. At over 500,000  kilometres long, the German gas distribution network is capable of supplying most residential buildings and apartments in Germany with natural gas. Even so, it is simply not feasible to connect all households. In rural areas in particular, it may not be possible to lay the gas lines. Anyone intending to purchase a gas heating system should therefore contact their local gas supply company beforehand.  

A connection to the local gas grid is not required if the gas heating system is running on liquid gas rather than natural gas. These are gases that have been liquefied under pressure, sometimes very high pressure. The best-known types of liquid gas are butane and propane gases as well as LPG (liquefied petroleum gas) and LNG gas (liquefied natural gas). Compared to natural gas, liquid gas has a higher energy content. This means that a gas boiler needs less fuel to produce the same amount of heat. If you wish to purchase a gas heating system that runs on liquid gas, you will need a tank to store the fuel. This can be placed either above ground or buried underground. Underground tanks are more expensive to purchase and must be monitored by TÜÜV.

The key to condensing technology is the utilisation of the heat of condensation. This is recovered when the combustion gases cool down and the water vapour releases the latent heat. In order for condensation to take place, system flow temperatures should be as low as possible. In specific terms, this means that the heating water flowing from the radiators back to the boiler must be as cool as possible. This is the only way to get the hot flue gases to condense. Underfloor heating systems and large-area radiators are particularly well suited to this operating mode.

Some components of the hot flue gases are acidic and can damage the chimney in the long term. Before homeowners purchase a gas heating system with condensing technology, they need to think about a suitable flue system that is approved for use with this.

Operating a gas condensing boiler creates condensate. To remove it, the condensate drain pipe must be fitted with a drain. The slightly acidic condensate can be discharged into the normal public sewage system without any problems. Only larger gas condensing boilers with a rated heating output of over 100  kW require the condensate to be neutralised before it is discharged. The deciding factor here is the pH value of the condensate. Code of Practice "DWA-A 251" of the German Association for Water, Wastewater and Waste (DWA) can generally be used as a guide. You will find a detailed description of this in the section on gas as a fuel.

Components of a flue gas system that are required for a gas condensing heating system

Benefits of modernising a gas heating system

There are still countless gas heating systems in use that utilise outdated technology and are a burden not only economically but also ecologically. By modernising their outdated gas heating system, homeowners benefit in many ways. But in order for the process to run smoothly, there are a few points to consider. Read more about the incentives and special considerations of modernisation here.

By choosing a gas condensing boiler, homeowners are actively doing their part to conserve resources and reduce the burden on the environment. By going one step further and using biogas, they can improve their environmental credentials even more. Technically, making this switch with a gas condensing boiler from Viessmann is not a problem. Thanks to the Lambda Pro Control combustion controller, the gas condensing boilers adjust automatically to different gas types –– including biogas mixtures. In addition to natural gas, biogas and liquid gas, the Vitodens products are also suitable for natural gas/hydrogen blends containing up to 20  percent hydrogen. Accordingly, they always convert the highest possible amount of energy into heat whatever the gas quality.

Another argument in favour of modernising old gas heating systems is the possibility of combining them with solar thermal energy. Every new gas heating system can and should be combined with solar collectors to use free solar energy. Viessmann gas boilers are prepared for connection to a solar thermal system. In just a few simple steps they can be switched from mono mode to dual mode. The solar thermal system is then able to provide all the DHW and serve as a backup for the heating system. The Viessmann system design guarantees that all components work together perfectly, right down to the convenient control unit –– even via the internet using an app that does everything you could ask of it.

Gas heating systems can be combined with heat pumps

For dual mode operation, a gas boiler can be combined not just with a solar thermal system but with a heat pump. In the case of the latter, the heat pump then not only provides DHW, but also heats the rooms. The gas boiler is switched on during peak loads. System owners are thus able to heat their homes extremely efficiently and cleanly whilst also conserving resources. Last but not least, the state supports such combinations with attractive subsidies, provided the boiler uses condensing technology. A gas heating system in an older building intelligently supplemented in this way will deliver optimum economic performance.

Problem-free installation

Since most connections lead directly into the house, the installation of a gas heating system is pretty straightforward. Once homeowners have opted for this type of heating system, a boiler can be installed almost anywhere. The compact wall mounted gas condensing boilers are space saving and can be installed quickly and easily in a utility room or basement. Whilst compact floorstanding appliances can be installed in an attic or ancillary room, homeowners can also easily hang gas condensing appliances in living spaces. There are even gas condensing boilers that fit in a kitchen cupboard.

No storage room necessary

With the connection being located directly in the house, homeowners do not need a storage room or a fuel tank to run a gas heating system. A tank is only required if they use liquid gas instead of natural gas. This can be installed in the garden, for example. An existing chimney is always required. When installing or mounting in the attic, a fireproof roof outlet with a small diameter of about ten centimetres is sufficient. If a chimney is available, the flue pipe can also be routed via the roof. If the gas heating system uses condensing technology, the flue pipes need to meet certain requirements.

More reasons

Mandatory replacement

The German Buildings Energy Act (GEG) requires that boilers installed before 1991 be replaced. These are now over 30 years old and consume an unnecessary amount of energy. However, mandatory replacement only applies to constant temperature boilers.

Value appreciation

Another reason for modernising the gas heating system is to increase the value of the property. A new and reliable gas boiler is a key factor influencing the desirability of a property, especially properties that have undergone structural redevelopment for use as rental apartments. New gas boilers are also very compact, meaning they take up little space when installed. Replacing the boiler therefore creates more space within the home.


In order to qualify for state subsidies from the Federal Funding for Energy-Efficient Buildings (BEG) programme to assist with the costs of modernisation projects, condensing technology must be used.

Heating with gas – a clean solution for commercial enterprises and local authorities

The gas boiler is a proven technology suitable for a variety of applications. With a portfolio offering outputs up to 2000 kW, Viessmann has the right solution for every need and budget. Technically speaking, we need to make a distinction here between low temperature and condensing technology. We'll explain what the difference is and what sets the two systems apart in commercial and municipal applications.

Gas condensing boilers with outputs of up to 2000 kW for commercial use

Gas condensing boilers additionally use the heat of condensation from the hot gases and thus achieve extremely high levels of efficiency. Here, the hot gases are not discharged as flue gases directly into the open air via the chimney, as is the case with conventional boilers. Instead, they flow through a heat exchanger and cool down in the process. As the gases cool, the water vapour contained in them condenses and releases the latent heat of condensation. This is then used to heat the heating water. In this way, the boiler has to do less work to bring the flow temperature up to the required level. Gas condensing boilers for commercial applications thus not only lower heating costs in the long term, but also help to reduce the amount of fossil fuels burned. This means that there is significantly less burden on the environment.

Viessmann's advanced gas condensing technology is noted for its use of Inox-Crossal heat exchangers made of stainless steel. These are ideally suited to condensing technology and can be found in all boilers in the Vitocrossal series in the output range between 80 and 1400 kilowatts. Vitocrossal condensing boilers are mainly used in apartment complexes, in public and commercial buildings and in local heating networks. Which type of boiler is best suited for the specific application should be determined through thorough project preparation and planning.

FAQs about heating with gas

What are the benefits of modernisation? How much can you save on energy costs with a new gas heating system? What does the forthcoming gas conversion mean? Isn't gas a finite fuel and how can I make myself independent of its price trends? The five most frequently asked questions about gas heating and their answers.

In the case of a boiler with conventional heating technology, savings of 15  percent are realistic. With an old constant temperature boiler, on the other hand, savings can be as much as 30  percent. If homeowners opt for a combination of gas condensing boiler and solar thermal energy as part of a heating system modernisation, their bills may be up to 35  percent lower than before. This is always assuming that the system components –– boiler, radiators, pump and pipework –– are all matched to each other.

In the coming years, many gas boilers will have to undergo technical conversion as part of the gas changeover in western Germany. Specifically, L-gas is being replaced by the more energy rich H-gas. Anyone owning a Viessmann gas condensing boiler with the Lambda Pro Control intelligent control unit is not affected by the conversion. This is because the control unit automatically adapts to the new gas type and can burn H-gas without any problems.

Those with gas condensing boilers not equipped with Viessmann's Lambda Pro Control intelligent control unit should take note of all letters, notices and deadlines received from their energy supplier. Consumers will not have to bear any of the costs incurred as a result of the conversion. You can find detailed information on this on the gas conversion page.

Those opting for tomorrow's technology today will be less dependent on their fuel supplier and will reduce their heating costs in the long run. This technology is here now in the following forms:

  • Solar thermal in combination with gas condensing boilers. Here, the solar thermal system is responsible for DHW heating and can relieve the burden on the heating system.
  • Gas condensing boiler and a heat pump. The gas condensing boiler is only switched on during peak loads.
  • Fuel cell heating system, such as the Vitovalor  300-P with peak load boiler which is only switched on when required

You can also find more information on gas heating in the guide to  gas hybrid appliances.

©️ MaximP /

Downloads and links for gas heating

In this section you will find all the important links and brochures for Viessmann gas boilers. All brochures are available for download free of charge as PDF files.

The following brochure provides you with information on condensing technology and its positive impact on the climate and the environment. Take a look and find out more about how this technology works, the wide range of gas condensing boilers and how they can be combined. The gas condensing technology brochure also provides the most important key data for individual appliances – summarised in a clear and easy-to-understand format.

Viessmann gas boilers are also available in the higher output range. The comprehensive range for commercial applications comprises efficient energy systems for the economic provision of heat, steam, refrigeration and power. The brochure covering gas boilers up to 2000  kW provides you with an overview of all heat generators for commercial applications.

Downloads library: brochures and datasheets for each model

Viessmann offers a wide range of models to meet every requirement. For detailed information, simply click on the respective datasheet and, if necessary, on the additional product information.

Wall mounted gas condensing boiler (heating appliance)
Rated heating output: 1.9 to 32  kW

Gas condensing storage combi boiler with integral stainless steel loading cylinder
Rated heating output: 1.9 to 32  kW

Gas/solar condensing storage combi boiler with solar DHW heating
Rated heating output: 1.9 to 19  kW

Gas condensing storage combi boiler with integral stainless steel loading cylinder
Rated heating output: 2.5 to 32  kW

Gas condensing storage combi boiler with integral 100  litre loading cylinder or 130  litre DHW cylinder with internal indirect coil  
Rated heating output: 2.5 to 32  kW

Gas condensing storage combi boiler for state of the art heating with condensing and solar technology in detached houses
Rated heating output: 2.5 to 19  kW

Wall mounted gas condensing boiler
Rated heating output from 49 to 150  kW
As a multi boiler system from 98 to 594  kW

Gas condensing boiler
Rated heating output: 400 to 630  kW, as a two-boiler system up to 1260  kW

*Manufacturer's declaration of convertibility to 100 % hydrogen in accordance with the Gebäudeenergiegesetz (GEG) at


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