| Boiling Point No. 22 - August 1990 |
by John McGeorge (A/ternative Sources of Energy, No. 35)
A tree is a pump that moves thousands of gallons of water from the ground up to its leaves every year. The leaves capture the sun's energy and provide sugars which are the building blocks of which leaves, bark, seeds and wood are made. The structure of the tree trunk and branches is what we use for fuel.
Freshly cut live trees are about 50% water. The water is locked up in the cell structure of the wood. Most wood cells are elongated tubular structures which run the length of the tree or its branches. As the wood dries, the cells empty. The loss of moisture is very important as it increases the heating value of the wood. If you examine the end of a seasoned log you will see checks and voids caused by the shrinking of the log as it dries.
As the wood dries out the weight decreases making it easier to handle. The decrease in moisture is also important because it dehydrates the various compounds which form creosote. When they are dry they will burn with the wood rather than evaporate and condense on the colder chimney walls and can cause serious chimney and roof fires.