The type and condition of firewood plays a key role in the quality of combustion. As a result, the consumer - user of a fireplace or wood-stove must take into account those factors that affect performance
Before we say anything about firewood, it should be remembered that combustion is the combination of some material (in this case wood containing in various forms of carbon and hydrogen) with oxygen and their conversion to carbon dioxide, water and heat energy. In chemistry, we are talking about an "exothermic" reaction that occurs with heat release, yielding about 4.5 - 5.5 kWh per kilogram of dry wood.
Among the different forest species we find different chemical composition, density and structure, which has a direct impact on the final product, ie on firewood and consequently on combustion.
Indicatively, the firth density is about 400 kg / m3, pine 500-550 kg / m3, beech 700-750 kg / m3, and oak 750-800 kg / m3. This means that in order to get the same amount of energy, in the form of heat when burning wood, we will need double the volume of fir than the oak. It is generally advisable to use woods with a density of more than 550 kg / m3, but this does not preclude the use of fir, provided it is available in an area (as is the case in Pertouli, where there is fir forest).
In general, conifers (especially pine trees) contain resins, especially in their bark, and this results in much smoke being produced during their burning, while beech and oak are characterized by cleaner combustion.
It is easier to burn woods with large pores (which allow the entry of oxygen) and this has to do with the type of tree and not with its origin.
The oak is considered particularly suitable for combustion. In Greece, we have 10 species of oak, of which 8 are burned well, while the other two are not. But these can not be distinguished by the naked eye (neither consumers nor traders), special knowledge and microscopic examination are required. However, loggers should know the varieties, depending on the area in which they operate. An example of burning wood is the white oak of Holomont.
On the other hand, acacia, although highly densified and considered "heavy" wood, does not burn easily because it has small pores.
In general, the kind of wood we use depends on availability. In the islands and in olive groves, the olive is widely used, it keeps "enough" as it does not have much flame and burns more slowly than other woods.
Apart from the quality and type of firewood, a factor that influences the combustion is moisture.
When a tree is cut, the resulting firewood moisture varies from 50% to 100% (!), Depending on the time of felling. In order to burn wood properly, its moisture content should be lowered to at least 20%, while moisture is ideal when it is between 12% and 15%. If the wood is cut in the spring or even in June and let it dry under a shed , in a well ventilated area, it's fine to burn them in the winter.
However, this does not seem to be the case, and wood merchants often sell "fresh" woods that do not light easily, and even when they light up, they consume much of the energy they produce to eliminate the moisture they contain. So firewood should be purchased at least one semester before using them and not at the last minute.
The view that trees on sunless slopes are burning harder is just a belief - it has no scientific evidence. Nor does the country of origin play a role. The same variety of oak, when it has the same moisture, will burn the same way either from Greece, either from Bulgaria or from Romania.
Oak: it gives a nice flame, it has a high density and a long burning time
Acacia: Hardwood with high density, suitable for burning, burns faster than the oak
Pine: soft, grasps easily, quickly gives a big flame, burns quickly but leaves a lot of residue in the chimney
Fir: it grasps easily, it gives a big flame and burns relatively quickly (we prefer white and we avoid red fir because we can have "cracks" during burning)
Pournari: Hardwood, particularly suitable for burning, but scarce
Olive: gives less flame, but lasts longer
Mechanical Engineer - Journalist Nikos Loupakis