Firewood Properties Table

Available Heat: Available heat is a measure of the heat given off when wood is burnt and is measured in kilojoules per gram of wood. A piece of hardwood gives off more energy than a piece of softwood because it is denser. 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 denser 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 more complex grain. Knots, branches and other 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 denser 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. The drier the wood the easier it is to light.

Moisture Content
Firewood should be dried to10% to 20% moisture content for best performance. A large proportion of the energy generated from burning green firewood actually goes to evaporating the water held in the wood. Green firewood
only gives off about 40% of the energy of dry firewood. To get the best out of your firewood it should be cut, split and stacked in a dry, 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.

Source: State of Victoria (2004) 'Properties of Firewood', Table 1. Timber properties of Victorian firewood species, [AG1150], pp. 2.