Regarding Seasoning of Wood
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. 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). thus, 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. Don't Do It!
Generally, the way this drying is accomplished is by "seasoning" it. Firewood is cut to length and then seasoned (dried) in a stack, with air being able to get to it, for at least 9 months before burning. 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.
There are a few things you can look for to see if the wood you intend to purchase is seasoned or not. Well seasoned firewood generally has darkened ends with cracks or splits visible, it is relatively lightweight, and makes a clear "clunk" when two pieces are beat together. Green wood on the other hand is very heavy, the ends look fresher, and it tends to make a dull "thud" when struck. These clues can fool you however, and by far the best way to be sure you have good wood when you need it is to buy your wood the spring before you intend to burn it and store it properly.