The carbon stored in wood, which was originally taken from the CO₂ in the atmosphere, combines once again with the oxygen in the air when the wood is burned. In the process, the same amount of CO₂ that was originally stored is released as was once taken from the air. This means that burning wood is completely CO₂-neutral!
The quality of the fuel is crucial for low-emission and efficient wood-fired heating. The wood must be clean and free from mould or rot. The moisture content must not exceed 25% under any circumstances; the drier the wood, the more efficient and environmentally friendly your heating will be. The wood should be left to dry for at least two to three years to achieve the optimum dryness.
Modern wood gasification boilers operate very efficiently and comply with all statutory emissions and dust limits. This requires high-quality wood to ensure the heating system can be operated in an environmentally friendly and low-emission manner. If, for example, wood that is too damp is burned, more than a fifth of the energy is lost to drying the wood in the boiler. This causes efficiency to drop significantly and increases the environmental impact caused by poorly burnt wood.
Firewood intended for burning should be clean and as dry as possible. Under no circumstances should treated wood (impregnated or varnished), chipboard, plastics or other waste be burned. This is prohibited by law and may also result in the loss of the manufacturer’s warranty.
Freshly felled wood usually has a high moisture content. Coniferous wood has a moisture content of around 55–70% (water content 35–41%), whilst hardwoods have a moisture content of around 70–100% (water content 41–50%). For the wood to burn properly, the moisture content should ideally be below 20% (water content < 16%). To achieve this, the wood must be stored in a dry place for at least a year before it can be burned.
Different units of volume are used for timber. A distinction is made between cubic metres, solid cubic metres and loose cubic metres. A cubic metre refers to stacked logs with external dimensions of 1 m × 1 m × 1 m. The gaps are included in the calculation. A cubic metre of loose volume, on the other hand, consists of wood that has been loosely poured into a container measuring 1 m x 1 m x 1 m. Here too, the gaps are included in the calculation. There are no gaps in a solid cubic metre. This consists of 1 m³ of solid wood with no gaps.
When wood is heated, water vapour and oxygen are released from 150°C onwards. As the temperature rises, the lignin and cellulose contained in the wood also gasify, producing a combustible mixture of gases. When air is supplied, this so-called wood gas ignites at a temperature of around 230–280°C. It is therefore not the wood that burns, but the escaping wood gases. What remains are the solid residues: ash and charcoal.
Contrary to some opinions and claims, wood-burning heating systems are not generally banned in Germany. In fact, they are still used in many private households and even in some commercial premises. However, there are certain regulations and guidelines that must be observed to ensure environmental protection.
Under this legislation, wood-fired heating systems must comply with specific emission limits to protect air quality. In particular, newer wood-fired heating systems installed from 2015 onwards must meet strict requirements to ensure combustion that is as environmentally friendly as possible. At Windhager, we recommend avoiding wood-fired heating systems in new builds and opting instead for subsidised heating models such as pellet systems or heat pumps.
