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fuel wood





fuel wood
Wood and wood products, possibly including coppices, scrubs, branches, etc., bought or gathered, and used by direct combustion.

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 wood of any species has a calorific value of approximately 8,600 BTU. Any moisture in the wood cuts down the recoverable heat by carrying heat up the chimney during vaporization. Additional heat is lost through volatile liquids and gases that form during combustion, but these vary by the type of heating unit and should be considered part of the efficiency factor of the heating unit.

A pound of wood with a 20% moisture content contains 0.17 pound of water and 0.83 pound of completely dry wood and has a heat value of about 7,000 BTU.


Best woods for burning

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 advantages of drying wood to at least a 20-percent moisture level are indicated in the table below.


  Pounds
green1
Pounds
air-dried2
Million BTU
available3
Ash 3,940 3,370 23.6
Basswood 3,360 2,100 14.7
Box elder 3,500 2,500 17.5
Cottonwood 3,920 2,304 16.1
Elm (American) 4,293 2,868 20.1
Elm (red) 4,480 3,056 21.4
Hackberry 4,000 3,080 21.6
Hickory (shagbark) 4,980 4,160 29.1
Locust (black) 4,640 4,010 28.1
Maple (silver) 3,783 2,970 20.8
Maple (sugar) 4,386 3,577 25.0
Oak (red) 4,988 3,609 25.3
Oak (white) 4,942 3,863 27.0
Osage orange 5,480 4,380 30.7
Pine (shortleaf) 4,120 2,713 19.0
Red cedar 3,260 2,700 18.9
Sycamore 4,160 2,956 20.7
Walnut (black) 4,640 3,120 21.8

1 Approximate weight of standard cord, for the first two columns of figures.
2 To 20% moisture content.
3 Potential available heat from standard cord with 100% unit efficiency. Heat at 20% moisture content.



Related categories

   • WOOD HEATING
   • FIRES AND FIREPLACES
   • FUELS