Practically any wood is excellent fuel when dry, were it birch or pine. In relation to weight, all wood species have the same heat energy content. One kilogram of birch releases the same amount of heat energy as one kilogram of spruce.
Spruce is the lightest firewood used in Finland. The weight of the wood matter may also vary inside one and the same wood species. A slowly grown tree is usually heavier than a fast grown.
Quality Criteria – Warm and Dry Wood
The most important quality criterion for firewood is sufficiently low moisture content. Good firewood has the moisture content of no higher than 15–20 %. The drier the wood is, the more energy-efficient it is to burn it. Energy-efficiency declines rapidly if the moisture content is high, which is the case with freshly cut trees. Read more about wood’s moisture content and its effect on energy-efficiency here.
Burning experiments on firewood show that another important factor, besides the low moisture content of the wood, is that the wood is already warm when used. It is worth considering getting an underfloor heating in the wood storage. It will soon pay for itself.
If the wood storage is not heated, firewood should be brought inside to warm up at least 24 hours before burning it. The consumption is a lot smaller this way, and the energy-efficiency the highest possible.
Because of the considerable increase in the trade of ready-to-use firewood, quality standards have been created. Grading of firewood is defined in the SFS-EN 14961-5 standard, and it is divided into three grades: A1, A2 and B. The seller is obligated to report the grade of the wood s/he is selling.
High-quality raw material for firewood.