Wood fuel is wood used as fuel. The burning of wood is currently the largest use of energy derived from a solid fuel biomass. Wood fuel can be used for cooking and heating, and occasionally for fueling steam engines and steam turbines that generate electricity. Wood fuel may be available as firewood (eg. logs, bolts, blocks), charcoal, chips, sheets, pellets and sawdust. The particular form used depends upon factors such as source, quantity, quality and application. Sawmill waste and construction industry by-products also include various forms of lumber tailings.

Wood may be burned in a furnace, stove, fireplace, or in a campfire, or used for a bonfire. Wood is the most easily available form of fuel, requiring no tools in the case of picking up dead wood, or little tools, although as in any industry, specialized tools, such as skidders and hydraulic wood splitters, have evolved to mechanize production.

The discovery of how to make fire for the purpose of burning wood is regarded as one of humanity's most important advances.

Clearly there are different types of wood, but they will usually fall into either the hardwood or softwood types. Both types of wood have the same energy content (by mass) and will provide similar energy outputs. However, the essential difference will be in the rate at which the fuel burns. Hardwoods derived from slow-growing broadleaf trees will burn at a slower rate for sustained output. Softwoods are derived from evergreen trees such as conifers, which are fast growing but burn at a far greater rate.

A common hardwood, red oak, weighs 3757 pounds per cord, with an energy content of 24 million BTU per cord, and 16.8 million recoverable BTU if burned at 70% efficiency.

The Sustainable Energy Development Office (SEDO), part of the Government of Western Australia states that the energy content of wood is 4.5 kWh/kg or 16.2 gigajoules/tonne (GJ/t).

Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License)

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Firewood Type Burning Efficiency
Wood Fuel & Energy