COUNTY AG NEWS

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Wood fuel for heating

 

Wood is a plentiful and accessible fuel for many in the Central and Northern parts of Wisconsin. Heating your home with wood can be less expensive than other sources of home heating energy, and firewood is a renewable resource. Prices of heating fuels vary considerably, but non-renewable fossil fuels and electricity are commonly 2 to more than 10 times more expensive than firewood for the same amount of heat.

Wood, however, does have disadvantages for industrial or home heating. Wood takes up more storage space. Wood must be dry for best performance and should be cut and split a year ahead of use. There is a chimney-fire hazard because low pipe or flue temperatures cause tars and creosote to condense. The increased price of oil based fuels has raised the level of interest in renewable fuels which include wood. New efficient heating and fuel preparation systems also increase the popularity of wood as fuel. When wood burns, three things happen: water is removed by evaporation; chemically, the wood breaks down into charcoal, gas and volatile liquids, with carbon dioxide and water being the chief end products; the charcoal burns, forming carbon dioxide either directly or with an intermediate conversion to carbon monoxide.

One pound of very dry (zero moisture content) wood of any species has a calorific value of approximately 8,600 BTU (British thermal unit, which equals the amount of heat required to raise the temperature of one pound of water one degree F). Any moisture in the wood reduces the recoverable heat by carrying heat up the chimney during vaporization. Each pound of water vaporized uses about 1,200 BTU.

Fresh cut wood will have a moisture content of around 50 percent. This wood when burned will have the sap in the wood bubble out of the bark on the ends of the piece of wood. Wood that has been allowed to air-dry for one year will have a moisture content of about 20 percent. A pound of wood with 20 percent moisture has a heat value of about 7,000 BTU. The fuel value of wood varies by the type of wood and depends on its density and moisture content. Any wood will burn, but the denser (heavier) woods, if properly dried, will deliver more BTU per cord.

 

The heating efficiency varies greatly depending on the heating unit. Fireplaces are great to look at but are anything but efficient. Most usually lose more heat than they generate. If you use a stove or furnace that is properly designed, constructed and installed, you will probably be obtaining around 50-percent efficiency.

 

Some of the stoves available now promise efficiencies as high as 85 percent. The heating unit must be well designed and constructed and used with a properly constructed chimney that is in good repair and free from tars and creosote. The unit must be set on an inflammable base large enough so coals and sparks cannot spill onto a flammable floor surface.

Be sure to locate the stove and pipes an adequate distance from walls and ceilings. Wood, clothing and other flammable materials must be kept a safe distance from the heating unit. Keep oils, gases and other volatile materials stored in other buildings to prevent the open flame from igniting fumes.

When wood is harvested and seasoned properly and burned in an efficient and safe heating unit, it is a safe, efficient, economical and desirable fuel from a renewable resource.

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