Properties of firewood	AG1150
Gavin Brock, Box Hill February, 2004

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Wood is a natural substance and is subject to variation caused by many factors. The species and age of the tree, the climate in which it grows, and the effects of environmental events such as fire or flood can all impact on the timber produced by a tree. Table 1 shows the properties of some Victorian firewood species.

Properties of firewood

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

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.

Splitting

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

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.

Spitting/Sparks

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.

Environmental benefits

Dry wood is a relatively environmentally 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).

Plantation firewood is a potential renewable energy source as it can be readily regrown, especially with those species that will coppice from the cut stumps.

It can also be argued that burning plantation firewood is carbon neutral provided the trees are regrown as carbon released into the atmosphere during the combustion process is counteracted by the equivalent amount of CO2 being absorbed by the next crop of trees.

The use of native species can also provide environmental benefits such as an increase in biodiversity, improvement in remnant bushland areas and habitat for native fauna. Firewood plantations can be used to help alleviate land management problems such as erosion, salinity and rising water tables, and nutrient runoff into streams.

When planted as shelterbelts, woodlots can also have other economic benefits on the farm such as increased crop and stock production.

Table 1. Timber properties of Victorian firewood species

Firewood Species	Common name	Relative Heat Available/Unit Volume (%)	Air-dry Density (kg/m3)	Splitting	Ignition	Sparks (spitting)	Coals
Eucalyptus spp.	Mallee roots	100		Difficult	Poor	Few	Excellent
Casuarina spp.	Belah, Buloke	100	1121	Good	Poor	Few	Excellent
Eucalyptus microcarpa	Grey Box	100	1121	Difficult	Poor	Few	Excellent
Eucalyptus largiflorens	Black Box	98	1105	Difficult	Poor	Few	Excellent
Eucalyptus sideroxylon	Red Ironbark	97	1090	Difficult	Poor	Few	Excellent
Eucalyptus melliodora	Yellow Box	95	1090	Difficult	Poor	Few	Excellent
Eucalyptus cladocalyx	Sugar Gum	95	1070	Difficult	Poor	Few	Excellent
Eucalyptus polyanthemos	Red Box	94	1060	Difficult	Poor	Few	Excellent
Eucalyptus leucoxylon	Yellow Gum	90	1010	Difficult	Poor	Few	Excellent
Eucalyptus goniocalyx	Long-leaved Box	89	1010	Difficult	Poor	Few	Good
Eucalyptus globulus	Blue Gum	83	927	Fair	Fair	Few	Good
Eucalyptus camaldulensis	River Red Gum	81	915	Difficult	Poor	Moderate	Excellent
Eucalyptus macrorhyncha	Red Stringybark	80	890	Good	Good	Few	Good
Eucalyptus sieberi	Sivertop Ash	77	865	Good	Good	Few	Good
Eucalyptus viminalis	Manna Gum	76	855	Good	Good	Few	Good
Eucalyptus radiata	Narrow-leaved Peppermint	73	820	Excellent	Good	Few	Good
Eucalyptus rubida	Candlebark	70	785	Good	Good	Few	Fair
Eucalyptus obliqua	Messmate	69	771	Good	Good	Few	Good
Acacia spp.	Wattle	63	705	Excellent	Excellent	Few	Fair
Eucalyptus regnans	Mountain Ash	60	673	Excellent	Excellent	Moderate	Fair
Callitris columellaris	White Cypress Pine	60	673	Good	Excellent	Many	Poor
Pinus radiata	Radiata Pine	45	512	Fair	Excellent	Many	Poor

Further Information

Agriculture note: Growing Plantation Firewood

References

• Bootle, K.R. (1995). Wood in Australia: Types, properties and uses, McGraw Hill Book Company Australia Pty Ltd, Roseville, NSW.
• Bulman, P. (1995). Farmtree$ for the Mount Lofty Ranges; A regional agroforestry handbook. Primary Industries SA, Adelaide.
• England, M (1998), Farm Forestry Note 7/98 – Firewood Growing in the Adelaide Hills and Fleurieu Peninsula, Primary Industries and Resources SA.
• Forest Research and Development Branch – Forests Service No 26 (1994), Firewood from Victoria’s Forests, Conservation and Natural Resources.
• Sonogan, B. (2002). ‘Plantation Grown Firewood for Home Heating! What are the Obstacles?’ Agroforestry News, Autumn 2002 – Volume 11, Issue 2

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