Fruit-woods are dense and heavy but found only in limited quantities. Good screens are needed for fireplaces and other open-burning units. The fuel value of wood depends on the wood species, its density, and moisture content. Too much moisture in wood greatly reduces its fuel value. The amount of water in wood is expressed as a percentage of the weight of the wood when it is ovendry.
Some species have as much or more weight in water in greenwood as the wood weighs when ovendry.
Cottonwood, green, has 140 percent moisture content where fresh cut green ash has about 55 percent moisture. Air-drying wood to about 20 percent moisture requires up to 9 months and makes the wood acceptable for burning. Burning green wood provides only a portion of the potential heat value and contributes to smoking and creosote-tar formation in the flue. Moisture is not critical on a volume basis but has a great deal of significance by weight. A cubic foot of wet wood has about 85 percent of the energy of a cubic foot of oven-dry wood, since 1 pound of wood has enough energy to evaporate 6 pounds of water.