Properties of Firewood
Available heat is a measure of the heat given off when wood is burnt and is measured in kilojoules per gram (kJ/g) of wood. A piece of hardwood gives off more energy than a piece of softwood because it is more dense. However, the volatile oils in some softwoods can increase the heat output of these species.
Density is the amount of space a mass of firewood occupies, the more dense the wood the less space a given mass takes up, or the greater a particular volume of firewood weighs. For example, Sugar Gum is about twice as dense as Radiata Pine, so a cubic metre of Sugar Gum weighs approximately 1070kg, while a cubic metre of Pine weighs only about 512kg.
Wood with a straight grain is easier to split than wood with a tighter and more complex grain. Knots, branches, and defects can also increase the difficulty of splitting firewood. Dry wood is generally easier to split than green wood.
Ignition is an indication of the ease with which the firewood can be lit. Low density wood is easier to light than more dense wood. Woods with higher levels of volatile chemicals in their structure, such as conifers, will ignite and burn more readily than those with less volatile chemicals. Dry wood is easier to light than moist 'green' wood.
For best performance, firewood should be dried until it reaches between 10% to 20% moisture content. A large amount of the energy generated from burning 'green' firewood actually goes to evaporating the water held in the wood. Green firewood gives off about 40% of the energy of dry firewood. To get the best out of firewood, it should be cut, split, and stacked in a well ventilated area for at least six months before it is to be used.
This is highly dependent on the amount of extractives in the wood. Wood from conifers, which have a high resin content are particularly prone to spitting and causing sparks.
Firewood is an environmentally sustainable, clean fuel. It is low in sulphur emissions and leaves little ash residue when burnt in a conventional wood heater that complies with the Australian Standard (AS 4013). Unlike large-scale forestry operations, Bushies firewood is sourced from local trees that have been approved for removal by local councils.