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Oil heating – proven efficiency, advanced technology

A blue-yellow flame produced by an oil boiler

Oil heating systems have been in use for decades. They are characterised by their high operational reliability and economic efficiency. One in four heat generators still uses crude oil to heat the building to the required temperature. This shows the important role that oil heating still plays.

From detached houses with a low heat demand to apartment buildings and large scale industrial projects: we have the right oil boiler with the corresponding heating technology for every need. While buildings with a very high heat demand are reliably and safely heated with oil condensing boilers or low temperature oil boilers, oil heating systems with condensing technology are now mandatory in residential buildings up to 400 kilowatts (kW).

Benefits at a glance

Highly reliable
Established technology in use for decades
Easy maintenance and repair
Secure supply thanks to numerous importing countries (up to 30 producing countries)
Diversity of suppliers allows more cost effective ordering of oil
Low cost operation with efficient heating technology
Can also be used in new buildings
Diverse combinations possible
Futureproof control technology

How does oil heating work?

In addition to the measurable heat (net calorific value), hot flue gases with temperatures up to 200 degrees Celsius are produced when oil is burned. Depending on the composition of the fuel oil used, the components of the flue gases vary in acidity and can damage both the oil boiler itself and the flue pipes, including the chimney. For this reason, low temperature oil boilers route the flue gases directly into the open air so that condensation does not occur. An oil boiler with condensing technology addresses precisely this issue by deliberately causing the flue gases to condense. The heat of condensation released in the process is utilised in the heating system, reducing the load on the oil boiler – and saving money for the system owner. More information on this topic can be found in the section on How oil condensing technology works.

Condensing technology means resource efficiency

Condensing boilers extract almost all of the heat in flue gases and convert it into additional heating energy. To do this, Viessmann condensing boilers are equipped with stainless steel Inox-Radial heat exchangers. These cool the flue gases before they are routed into the chimney, to the extent that the water vapour contained in these gases is deliberately condensed. Additional heat is then released and transferred into the heating system. This reduces heating costs in the long run and also protects the environment. After all, less fossil fuel needs to be burned for the same amount of heat.

Condensate on a heat exchanger is a classic symbol of oil heating.

High efficiency of oil heating

By purchasing a condensing boiler, you are making an active contribution to conserving resources and saving energy. The efficiency of these boilers is unbeatably high, with up to 98  percent of the fuel oil used converted into heat. For system owners, this means low heating costs.

Requirements for the operation of an oil condensing heating system

A few things are needed for the operation of an oil condensing boiler. Oil condensing boilers are characterised by the fact that they cool the combustion gases and cause them to condense. For this to work, the flue gases are routed past the cool return water. If the temperature of this return water is too high, condensation will not occur. For this reason, it is important that the flow temperature is as low as possible. This can primarily be achieved with large heating surfaces such as underfloor heating or wall heating.  

In addition, the acidic components in the condensate can damage the flue system in the long term. When buying an oil heating system, homeowners should therefore look for a suitable flue system that is resistant to water and acid. The acidic water must also be disposed of. Therefore, it is essential that homeowners think about condensate drainage before buying an oil boiler. As a rule, the condensate can be discharged directly into the waste water. In a few cases, however, neutralisation is necessary before discharge.

The density of the flue gases is also reduced. A natural draught into the open is no longer possible due to the low density differences.  For this reason, a fan (e.g. burner fan) must be used.

Fuel oil and oil tank – did you know?

Not all fuel oil is the same. In Germany, fuel oil is standardised. DIN 51603-1 and DIN SPEC 51603-6 classify fuel oil into:

  • Standard EL fuel oil
  • Low sulphur EL fuel oil 
  • Biofuel oil

Standard EL fuel oil is no longer produced in Germany. Almost all private households use low sulphur EL fuel oil instead. This was originally developed for condensing technology. However, thanks to its numerous advantages, such as clean and almost odourless combustion and reduction of the sulphur content by about 20 percent, low sulphur EL fuel oil has now become firmly established. EL stands for "extra light" and indicates low viscosity. Oil condensing boilers that burn only low sulphur EL fuel oil must be fitted with a green fill pipe cover.

In addition to low sulphur EL fuel oil, there is also premium fuel oil and biofuel oil. Compared to "standard EL fuel oil", the premium version contains special additives that, for example, extend the storage period or reduce deposits. Biofuel oil, on the other hand, is produced from regenerative raw materials such as rapeseed, sunflowers or soy beans and is added to the low sulphur EL fuel oil. The gross calorific value of fuel oil is approximately 45.5 MJ/kg. This corresponds to 10.74 kilowatts per litre. In comparison, natural gas has a gross calorific value of about 36 to 50 MJ/kg. However, the gross calorific value of oil may vary slightly depending on the grade. Suppliers often specify the gross calorific value of oil in addition to the net calorific value when an order is placed.

Futureproof heating technology with new bio-oil

With oil heating, you can stay at the cutting edge of technology in the future too. Our oil boilers are supplied ready equipped to accommodate a changeover from fossil oil to fuel oil mixed with a certain percentage of bio-oil, and so can also be used with renewable fuel types. In this way, you actively contribute to environmental protection and also keep heating costs at a low level. A long term final switch to renewable fuels such as using environmental energy with a heat pump or biomass with a solid fuel boiler can be realised step by step.

Green fuels  

The latest generation of liquid fuel boilers from Viessmann is prepared for the use of green fuels. Learn more about liquid fuels in the video.       

The oil tank as an important component of an oil heating system

A store of fuel oil is necessary so that it can enter the combustion chamber automatically and in the correct amount. The tank required for this is usually made of metal or plastic. In order to reduce the risk of leaks, many tanks are twin wall and also have safety components such as a limit transducer or other measuring instruments.

Guidelines for oil tanks, including in flood zones

Fuel oil can be stored either above ground or underground. For the above-ground version, a site-built or modular tank may be considered. Regardless of how it is installed, every oil tank must meet high safety standards. These are strictly laid out in the German "Ordinance on facilities for handling substances that are hazardous to water" (AwSV). This regulation stipulates that tanks with a capacity of more than 5000  litres must be placed in a separate room. The installation room itself must also meet certain requirements and, for example, have a self-closing door or a fire rating. If the tank is located in a flood zone, the entire system must be flood-proof. As a general rule: both the installation and the dismantling of an oil tank may only be carried out by a specialist contractor.

A selection of solar thermal systems that can be combined with oil heating

Improve the life cycle assessment of an oil heating system

When buying a new oil boiler, it is also important to take into consideration the life cycle assessment. This can be improved if homeowners connect their oil boiler to another heating system. This can be either a solar thermal system or a heat pump. In both cases, system owners heat in an extremely environmentally responsible and economical way, as both heating systems access free and almost infinite heat sources.

Combine oil heating with solar technology and use free solar energy

A new oil heating system can be combined with free solar energy: all our boilers are designed for the connection of a solar thermal system for DHW heating or central heating backup. In dual mode operation, the solar thermal system provides DHW heating and can almost completely replace the oil boiler during spring and autumn.

The combination permanently reduces heating costs and also protects the environment. In addition, solar technology gives you a certain degree of independence from your fuel supplier. From the control unit to spare parts and control via app, the system technology used guarantees interaction between all components.

Why should you modernise your oil heating system if it is still working?

Older boilers work inefficiently and consume much more fuel than necessary. They are also much more susceptible to defects and failures, which usually happen when heating energy is needed most. In both cases, this leads to high heating costs. In addition, oil heating systems burn oil to generate heat. Burning oil produces harmful gases such as carbon dioxide, which is a major contributor to global warming. Since new boilers burn less oil for the same amount of heat, they not only save money for system owners, but also lessen the impact on the environment. 

Replacement is sometimes mandatory

The burden on the environment caused by inefficient boilers is the reason why the German Buildings Energy Act (GEG) requires boilers to be replaced. Specifically, system owners must decommission or replace their boilers if they were commissioned before 1989. However, only constant temperature boilers are affected by this replacement obligation. Anyone who has a low temperature boiler or condensing boiler in their basement is exempt from this requirement. Nevertheless, replacement of a boiler that is more than 30 years old is recommended for the reasons mentioned above.

Oil heating systems for local authorities and commercial applications

As already explained, the technology used in oil heating systems has been tried and tested over many years, is reliable in operation and a guarantee for economical use. Viessmann oil boilers are available in numerous output stages. For commercial use, Viessmann's product range includes oil condensing boilers with a rated heating output of up to 545 kW and low temperature oil boilers up to 2000 kW.

Which boiler type is best suited to the specific application – low temperature or condensing oil boiler – must be checked as part of comprehensive preparation and planning of the project.

The advantages of low temperature oil boilers

Constant temperature boilers are outdated. They were operated at a constant boiler water temperature regardless of demand and therefore without taking weather conditions into account. As a result, a lot of the energy was unused and lost. Advanced low temperature oil boilers, on the other hand, adjust their boiler water temperature precisely to the current weather conditions and heat demand.

When it comes to proven heating technology in the medium output range, Viessmann's low temperature oil boilers meet all the requirements of state of the art heating technology. With a rated heating output of up to 2000 kW, they economically and reliably cover the high heat demand often found in commercial sectors. Thanks to their sectional design, Viessmann cast iron low temperature gas boilers are easy to manoeuvre and quick and simple to install. This means that installation is possible without any problems even in confined spaces. Low temperature oil boilers from Viessmann are suitable for commercial enterprises and local authorities, both for new build and modernisation.

Downloads for oil heating systems

Cast iron oil condensing boiler with a rated heating output of 20.2 to 107.3  kW

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