Using wet or fresh wood for a fire
In simple terms, the word ‘seasoned’ means ‘dry’ and the term ‘green’ means ‘freshly cut from living tree’.
Why is it not a good idea to burn green wood on a fire?
Green wood carries about a third of its weight as water, which on the fire evaporates and helps to carry the heat away up the chimney. You can often hear a log sizzle or hiss in the fire if it is too green or damp.
How do I know if wood has been seasoned?
It’s essential to know that the wood you are buying is properly seasoned and not still full of moisture. Here are some quick checks to help you tell the difference:
- Seasoned wood weighs much less than green wood.
- Seasoned wood looks darker, or grey when compared to freshly cut or “green” wood which is usually more yellow or cream coloured.
- Seasoned wood will have drying cracks showing at the flat, cut end.
- Seasoned wood will have loose bark compared to the bark of green wood which will be tightly attached.
- When two pieces of seasoned wood are knocked together they make a high, hollow sound whereas green wood makes a more dull sound.
- Seasoned wood should not hiss when burnt, this is the water in the wood boiling and being forced out as steam.
What to do if you buy wood that has not been seasoned
If you buy logs which have not been seasoned, you should cut them to length (300mm or 10″ to 18″), split to size and stacked. Tree branches and trunks contain thousands of microscopic tubes which carry water from the roots to the leaves, and these tubes can stay full of water for years after the tree has been felled (or pruned). Cutting the wood to shorter lengths opens these tubes to the atmosphere which increases evaporation.
The stack should be completely covered on the top to prevent rain wetting the wood but air must be allowed to reach the sides of the stack. Leave to season for at least 1 year (more if possible). Some logs may take 3 to 4 years to fully season. Bring the fuel into the house a few days before you want to use it to get it as dry as possible.
All wood will, when supported by lots of kindling and/or a good ember base, will burn unseasoned. However, you may find some woods are not worth using in this state due to the length of ‘hissing’ time (as the water boils from within the wood) before they can burn.
Moisture content of firewood
- by volume wet wood has about 85% of the energy of oven-dry wood
- by weight wet wood has less than half – 42% – of the energy of oven-dry wood