FIREWOOD AS FUEL
Article #101, November, 2005
By Bill Cook
Most of us who burn wood have already dug into the winter supply. The frosts are coming regularly and the days seldom get warm enough to leave the house unheated for long. Nothing beats the feel of wood heat, but do the costs compete with other fuel sources?
Well, if we have only our own free labor and the expense of a few gallons of gasoline, then of course wood heat makes sense. Not only does it heat the house during the winter but it keeps warm the person doing the cutting and splitting.
what if you have to buy cut and split firewood? How much should you pay if the
objective is to heat cheaper than using fossil fuels? The answer depends upon
the price of the fuel, species of wood, the type of stove or furnace, and wood
Wood sold by the standard cord is equivalent to a stack of eight foot logs four feet tall and four feet wide. Green weights will be about 4000-5000 pounds per cord, depending upon the species. Dry weights will run 1500-4000 pounds per cord.
Let's assume fuel oil costs $3.00 per gallon and propane $1.85 per gallon. If you have a high efficiency wood stove, you should be able to afford wood at any going price and be ahead money. If you have only a fireplace, then you could only afford about $25-40 per cord in order to break even with oil or propane. Of course, folks with fireplaces don't usually burn wood for dollar savings, but rather for aesthetic purposes or as a supplement. In this case, cost isn't really an issue.
Not all species of firewood are created equal in terms of available heat energy per cord. Remember that a cord is a volume measure, not a weight measure. Of course, well-seasoned wood is always much better than green or wet firewood. Apple, sugar maple, red oak, beech and yellow birch are among the best species from the northwoods. Tamarack, cherry, elm, paper birch, red maple, and black ash are intermediate. Pine, fir, spruce, aspen, and basswood hold the least amount of energy per cord.
The reason why firewood is better after it's well-dried has to do with energy needed to evaporate water. Before wood can burn, it has to be nearly free of water. A fire will drive water out of the wood as steam. That takes energy which would have otherwise been available to heat your room or house. The monetary difference between dry and wet wood can run up to 35-40 dollars per cord of equivalent fossil fuel costs.
Additionally, it takes energy to "denature" the solid wood into gases. It's actually the gases that burn, not the wood itself. It takes energy in the wood to produce the gases. These are the reasons for differences in total BTU values and "available" BTU values. As you might imagine, these sets of values can vary considerably with the condition and species of wood that you use.
All of these figures and comparisons are generalities because there are many ways to skin the home heating cat. Another area with many variables is the efficiency of the heating system. We have everything from the old barrel stoves to hi-tech heat transfer systems. Some of them probably even work! The upshot with the hi-tech part of the equation is that more heat energy can be captured to heat your house and less is sent out into the cold winter air. Using better quality and well-dried wood will maximize the cost-savings of any system.
Something else to consider these days are the many forest pest problems that can be spread by moving around firewood. The emerald ash borer is most commonly spread by firewood and has been in the news a lot lately. However, pests such as gypsy moth, oak wilt, beech bark disease, and other hitch-hikers also get distributed by firewood movement. Also, there are plenty of "new" exotic pests over the horizon just waiting for careless firewood traffickers. It's a good idea to develop the habit of burning everything that you cut for the winter, before the next growing season.
Lastly, remember to keep safety in mind. Caution with those chainsaws and splitting mauls. Clean the chimneys and maintain the furnaces. Medical bills will eat up everything you might save by heating with wood.
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Bill Cook is an MSU Extension forester providing educational programming for the entire Upper Peninsula. His office is located at the MSU Upper Peninsula Tree Improvement Center near Escanaba. The Center is the headquarters for three MSU Forestry properties in the U.P., with a combined area of about 8,000 acres. He can be reached at firstname.lastname@example.org or 906-786-1575.
by Bill Cook, Forester/Biologist, Michigan State University Extension, 6005
J Road, Escanaba, MI 49829
906-786-1575 (voice), 906-786-9370 (fax), e-mail: email@example.com
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