University of Illinois Extension

 

John Church,
Unit Educator, Horticulture
Winnebago/Boone Counties

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Heating with Wood Needs Care and Consideration

As people remember last winter’s high energy costs, many people may use this fall as a good time to gather wood for heating the home. Remember that although wood can be a good source of heat, it should be used with caution and proper maintenance should be done to avoid fires and chimney problems. Care should also be taken to ensure that the use of wood is really more efficient and economical for the home than the use of routine heat sources.

When considering the use of wood for heat, University of Illinois Extension foresters offer the following information and advice: All species of wood has the same Btu (British Thermal Units) per pound of wood; roughly 8600 Btu per pound @ 15% moisture content. As the moisture content goes up in the firewood, the heating value goes down (less Btu's) because more energy (heat) is needed to drive off the moisture in the wood before it will burn. This is why firewood needs to be seasoned at least 6 to 9 months before it is burned. Freshly cut wood is not very efficient for heating use.

The difference in the heating value of different species of trees comes in the density (weight per unit of volume) of the wood species. If comparing two pieces of wood that are of identical size (volume) and moisture content and one is oak and one is cottonwood, the piece of oak firewood will contain more Btu's (heat) in it than the cottonwood because the density of oak is much greater than cottonwood. Oak is a heavier wood than cottonwood, so oak will have more potential energy than cottonwood if the same size piece or stack (volume) of wood is compared.

Therefore, a cord of oak firewood would have 26.5 million Btu's of energy and a cord of cottonwood would have 16.1 million Btu's of energy, because a cord of oak weighs 3800 pounds and a cord of cottonwood weighs 2300 pounds. A cord is a stack of wood that is 4 feet high by 8 feet wide and each of the pieces is 4 feet in length or 4' x 8' x 4' = 128 cubic feet. The variety of wood and total Btu’s should be considered when purchasing and pricing cords of wood.

For more detailed information, there are several university Extension web sites across the country that offer good information on safely selecting, cutting, drying, storing, evaluating and pricing wood for firewood, including

North Carolina: http://www.ces.ncsu.edu/nreos/forest/woodland/won-14.html

October - November 2001: Preparing Plants for Winter | Heating with Wood Needs Care and Consideration | Amaryllis for Winter Beauty | Understanding Fall Color |

 

Past Issues

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