Firewood Guide, Meaning , Facts, Information and Description
Wood heatFirewood - usually relates to timber or trees unsuitable for building or construction, used as a solid fuel for cooking or heating, or occasionally for steam engines. Firewood is a renewable resource provided the consumption rate is controlled to sustainable levels. The shortage of suitable firewood in some places has seen local populations damaging huge tracts of bush thus leading to further desertification.
The largest current use of biomass derived energy, firewood is also a greenhouse gas neutral form of heating, since the combustion of the fuel releases the same amount of carbon dioxide as is bound up by growing the next generation of trees. However high levels of firewood consumption in urban areas can cause air pollution, particularly particulates. "Slow combustion stoves" increase efficiency of wood heaters, but also increase particulate production. Low pollution slow combustion stoves are a current area of research. An alternative approach is to use pyrolysis to produce several useful biochemical byproducts, and clean burning charcoal.
A by-product of firewood consumption is wood ash, which in moderate amounts is a fertiliser, but is strongly alkaline. Wood ash can also be used to manufacture soap.
The "caloric content" (energy content available from combustion) of firewood depends mainly on how dry it is. "Green" wood is about 10 MJ/kg (megajoule per kilogram), air-seasoned wood about 16 MJ/kg, while kiln dried wood is about 19 to 20 MJ/kg. The "caloric content" of firewood on a volume basis also depends upon the species of tree from which the wood is cut. In the United States, firewood is typically broadly classified into two categories: "hardwood" (any broadleaf tree) and "softwood" (any species of conifer). These labels are often misleading, as some species of conifer have harder wood than some species of broad-leaf tree. Generally, the harder the wood (which results from slower growth), the denser it is and the greater the amount of biomass per unit volume. Such woods, when well-seasoned, produce hot, long-burning fires with practically no particulate emissions. In the United States, varieties of wood such as Oak, Hard Maple, Hickory, and most of the fruit woods (apple, cherry, etc.) have the hardest, most dense wood, and are most desireable for firewood. Broad-leafed varieties such as willow, aspen, or poplar have less-dense wood and require a greater volume of wood to produce the same amount of heat. In areas where broad-leafed trees do not grow, varieties such as slash pine, Western Larch, and Yew are desireable varieties of firewood.
Some firewood is harvested in purpose grown "wood lots", but in heavily wooded areas it is more usually harvested from natural forests. Deadfall that has not started to rot is preferred, since it is already partly seasoned. Standing dead timber is considered better still, as it is both seasoned, and has less rot. Harvesting this form of timber reduces the speed and intensity of bushfires. Harvesting timber for firewood is normally carried out by hand with chainsaws. Thus, longer pieces - requiring less manual labour, and less chainsaw fuel - are less expensive (but the user must ensure that the lengths will fit in the firebox!) Prices also vary considerably with the distance from wood lots, and quality of the wood. In the United States, firewood is sold by the cord (a unit of volume equal to 4 by 4 by 8 feet, or 128 cubic feet), or by the "face cord", which is actually a unit of area, equal to 32 square feet (this unit of area is used exclusively for describing stacks of firewood). A pile of wood four feet high, eight feet long, and cut to, say, sixteen inch lengths will often be sold as a "face cord" of 16 inch logs, even though the actual volume of the wood pile is only one-third of a cord. Hence, only a "face cord" of 48 inch logs would actually equal a "cord" of firewood. In Australia, it is normally sold by the tonne. In Sweden it's sold by volume.