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Not only central heating, but also the fireplace, which is very popular today, relies on wood as a fuel. In general, people appreciate the low price, the good availability and also the ecological aspects of the material. However, not all wood is equally suitable for burning in the oven. Certain types of wood or wood-based materials are even completely unsuitable for combustion. We explain what they are and where burning is completely safe.
wood for the fireplace
The suitability of wood as a fuel can be determined by various characteristics. Because the type of wood, the processing, as well as individual properties can lead to the fact that it is a fuel that can be used without any problems, or that it can neither be burned nor allowed.
Suitable firewood
The most obvious thing is certainly to determine suitability as firewood based on the clearly identifiable type of wood:
oak and beech
- average weight around 700 to 710 kg per m³
- high calorific value
- long burning time
- relatively long ignition time
poplar
- average weight around 450 kg per m³
- low calorific value
- easy to ignite, rapid development of fire
- faster burn
- high ash content
Softwoods (spruce, fir, pine etc.)
- average weight depending on the species between 450 kg (spruce) and 600 kg (pine) per m³
- Relatively fast burning, usually faster than beech and oak, but slower than e.g. poplar
- very easy to ignite due to high resin content
- good burning properties
danger: When using firewood made from resinous softwoods, the fire should never be left unattended in an open fireplace. Due to the water content in the resin of the wood, the material tends to spatter when heated by the fire. An unintentional spread of fire to the areas in front of the fireplace can be quickly detected and prevented.
birch
- average weight around 620 kg per m³
- Calorific value under oak and beech, but significantly higher than coniferous wood
- Logs with bark are particularly easy to light, making them well suited as kindling
- Comparatively slower burn due to low resin content
ash
- average weight around 700 kg per m³
- high calorific value
- thin bark, therefore low smoke and soot development
- well suited for long-term heating
Fruit woods (cherry, plum, apple etc.)
- Average weight depending on the species between 500 kg and 600 to 650 kg per m³
- high calorific value
- Depending on the type, medium to slow burning rate
tip: Fruit wood is also very popular for other uses, such as furniture making or veneer cutting. While branches can hardly be used for this purpose, you should first consider selling thicker and undamaged trunks to a carpenter as an alternative, since otherwise good firewood is available, but at the same time high material values are being burned.
Combination of wood species
If you look at the descriptions of the individual types of wood, you can get the impression that some woods are well suited, others only moderately. The obvious approach now is to only burn the more suitable firewood if possible. However, a combination of several types of wood can also be useful. Because while beech, for example, has a very long burning time and a high calorific value due to its high weight, burning it together with poplar or softwood in the fireplace can mean a significantly higher level of comfort when lighting the fire and the general development of the fire. Furthermore, despite its lower calorific value, lighter wood can be very well suited for the cozy fire in the fireplace at home, simply because it burns faster and the actual calorific value is not at all in the foreground here.
Unsuitable types of wood
On the other hand, there are no types of wood that are completely unsuitable for burning in our latitudes. Although bushy trees and shrubs are not usually used as firewood, this is not due to the type of wood, but rather to the small cross-sections of the wood obtained and the associated very high burning rate and smoke and ash development.
The suitability after moisture
Another important suitability characteristic of firewood is its moisture content. If it is too high, the fuel can be ignited, but it will not continue to burn on its own. At lower humidity levels, the flammability is given, but it is also associated with extreme smoke development. This overview helps to assess the wood moisture content and suitability for combustion:
- Wood moisture content with proper felling in the growth-free period between 50% and 60%
- Decrease in wood moisture content with correct storage (well ventilated, not completely wrapped in foil, etc.) 20% to 30% per year
- Moisture content of around 20%, which makes sense for combustion, is reached after one to two years of storage
danger: According to the Federal Immission Control Ordinance (BImSchV), wood may only be burned with a maximum moisture content of 25%. Moist wood might technically be combustible under certain circumstances, but it must not be used as firewood.
Individual wood characteristics
Finally, there are various individual characteristics of the wood intended for use in the stove or fireplace, which can also lead to its unsuitability as a fuel:
fungal infection
Wood that is heavily infested with fungi should not be burned in the fireplace. Various fungal spores can cause skin and respiratory problems for humans. When burning, the spores are distributed in the room air by the strong air turbulence in the area of the fire and are thus transferred to the surroundings of the fireplace.
processing
Depending on how the wood is processed, such as pallets, furniture, chipboard, etc., toxic substances can be released into the ambient air during combustion, which can lead to significant health impairments in humans and at the same time represent a major environmental impact. Examples of critical firewood are:
- Pallets and other pressure treated wood
- Lacquered and otherwise coated wood
- Wood-based materials with a high proportion of glue or binder
- Combination building materials that contain other materials such as gypsum, cement, etc. in addition to wood