Freshly cut wood has a very high moisture content. As much as 60% (or more) of the weight of a tree is water. At least some of this water must be removed before trying to use it as a fuel wood (See below moisture content table). Several bad results can occur from burning wood that is not fully dried to below 25% moisture content. (Such wood is referred to as “green” wood). As that discussion mentions, the effective available heat is MUCH less, not just because there is less wood fibers in each pound of wood put in the woodburner, but that a good percentage of that heat must be used to evaporate all that water before those wood fibers can burn. Another VERY important consequence of burning green wood is that the presence of all that moisture tends to keep “putting out” the fire, and therefore making it burn very poorly, which tends to produce a lot of creosote and pollution.

 
Generally, the way this drying is accomplished is by “seasoning”  the wood. Firewood is cut to length, split and then seasoned (dried) in a stack, with air being able to get to it, for at least 9 months before burning (DEP states 6 months minimum). The natural 60%-70% moisture content must be reduced to about 20% to burn well. The wood cells don’t lose much moisture through the bark; the moisture is most effectively removed through the cut cells at the ends of each piece.

Something to consider when shopping for firewood is whether or not the cord wood is mixed species or all one type. If it’s all one type you can use the below chart to get an idea of which wood species need longer drying times. For example; if you are looking at a supplier who only sells ash then you can have a slightly higher confidence level its all seasoned since its at a much lower moisture content to begin with. Looking at the below chart will show that seasoning a cord of ash will take far less time then a cord of red oak. I have stacked split ash in the sun for 4 months and it was perfectly ready to burn, now if I stacked it in the shady woods I am sure it would have required another month or so to properly season.

Indicators of properly seasoned firewood.

• Color - Wood should have a dull grayness color
• Bark – a sure sign that firewood is dry is bark that is falling off the wood
• Weight – Dry wood weighs much less than wet wood (besure you are comparing the same wood species)
• Checks – as wood dries it will begin to split on the ends and display cracks
• Touch – Split a piece of wood. If the exposed surface feels damp, the wood is not sesoned
• Sound – two dry pieces banged together sound hollow; wet pieces sound solid and dull.

If there is a need to sometimes burn unseasoned wood (though not recommended) which species would be best under those conditions? It turns out that the desirability is NOT the same as for seasoned wood! While they are living, various species of trees have different moisture contents. If you suitably dry them all, that difference disappears. But, while still green, it becomes significant.

 It is possible to correlate both the heat-content of the wood fibers and the green moisture content to form a table of desirability for those situations when green wood must be burned.

Excess moisture is that percentage above the desirable 20% seasoned moisture content.

Tips on buying good firewood

• Ask friends and neighbours who burn wood for recommendations on reliable suppliers.
• Shop around and select the dealer who seems most reliable and comes with the best recommendations.
• Do not order wood by phone. Go to the storage area to inspect the wood and take a tape measure to check piece length and pile size.
• Look for wood that is clean. Sand and mud on firewood makes it less desirable.
• Either measure the piled wood before delivery or stack it (or have it stacked) at home before paying so you can measure it and confirm that you get the volume you pay for.
• If possible, get the wood in spring and stack it in your own yard so you can control the seasoning process.

For further information on firewood or to buy firewood from Bart’s Tree Service located in the Danbury CT area click here.