Contents at a Glance...
- When Collecting or Purchasing Firewood
Current estimates indicate that a massive 6.1 million tonnes of firewood 2 are collected each year in Australia. This is more than the 4.1 million tonnes we take out of our forests for woodchips.
When Collecting or Purchasing Firewood...
What to Avoid if Using Firewood:
Because of the rising cost of energy for heating, attention has been drawn to the possibility of using timber residues, such as sawdust, shavings and bark as a source of heating fuel 3.
Due to its fine particles, sawdust is not a viable fuel in its own right unless fed gradually into such as a commercial Dutch Oven. For domestic purposes, it would need to be dried and compressed into 'logs', briquettes or pellets. Bark could be processed in this way too, but is not a very attractive proposition due to its high ash content. Due to the energy-intensive nature of processing sawdust, etc, such a resource would only be commercially exploitable if a large supply existed close to a large market 4.
CLEARING THE AIR
Residential wood stove 5 emissions are documented as being a large source of particulate matter pollution and illness. Some stoves burn more cleanly than others, and many people still have old wood stoves that don't burn efficiently. There is, in fact, a growing demand for used stoves.
Emissions from a burning wood stove include:
IF YOU INSIST ON BURNING WOOD...
Instead of trying to save money by using a wood stove, it might make more sense to properly insulate your house, put in new, tight windows and doors and upgrade your existing heating system. But if your heart is set on having a wood stove, here are some guidelines:
NB: Do not burn treated wood, wrapping paper, coated paper, rubbish, or plastic in any wood stove. Use only seasoned hardwood. Generally, the hottest burning woods are the denser varieties, which burn more slowly.
See also the EPA leaflet Is Your Wood Going Up in Smoke)
In the U.S., stoves have been designed which burn a pellet made of sawdust and cardboard. One stove can heat 2,000 square feet, and will release only negligible amounts of airborne pollutants and ash.
- E Magazine, Feb '97
The average family of four uses about six to ten tonnes of firewood for heating an insulated house each year. (An uninsulated house uses up to 20 tonnes). The approximate potential heat value per dollar of wood is at least as good as, if not better than, other fuels. Wood heating can be cost-effective and enjoyable, especially if you can grow your own firewood. Most small property owners can grow firewood to meet or supplement their needs.
The time between planting and harvest and the quality of wood grown depends on the species, quality of the site, use of fertiliser, weed control and, particularly rainfall. The spacing of the trees is also important if larger, splittable logs are to be grown.
The table following provides a guide for an area to be planted to produce dry firewood. For example, 200mm rainfall will allow one hectare of trees to be planted at say, three-metre intervals and will yield about six dry tonnes of firewood in about nine years.
Firewood can be grown in planted woodlots or obtained from existing forests. In either case, an effective way to continuously produce firewood is to coppice. Most species of sheoaks, acacias and eucalypts will re-shoot from a cut stump. One stump produces many new trunks from dormant buds beneath the bark. Growth is quick because it is supported by a well established root system.
These trunks can be selectively harvested according to size. Posts and poles or even sawlogs could also be produced. Coppicing does not require any replanting and, once the trees are established, forest cover can be maintained. The best coppice, if left to grow larger, will provide a seed source in the event of a wildfire. And, harvesting wood may disturb the soil sufficiently to encourage natural regeneration from seed.
To ensure good coppice growth in southern Australia, cutting wood in late winter or spring is best. Cut the stumps close to the ground. About a year after coppicing, the stems can be cut back to about the original tree stocking-rate if desired.
Often 'firewood blocks' can be incorporated into the property to provide shelter, wildlife habitat or landscape.
Preparation is the key to good, early growth and survival. Deep ripping to a depth of at least 50 centimetres will aid establishment and should be done in autumn before the ground becomes too wet to work. Clear weeds prior to planting. Planting is best done in autumn. However, if the area is severly waterlogged or frost-prone during winter, planting should be carried out in spring.
Space rows three and a half to five metres apart to allow tractor access for slashing and extraction. In the rows, spacing between trees should be two and a half to four metres. You can thin out the plantation of ten to fifteen years to provide some fuel and allow the remaining trees to grow faster.
Tree guards may be necessary early-on in exposed areas if rabbits or hares are a problem. If possible, the fence surrounding the planted area should be stock-proof.
Weight for weight, all timbers have about the same calorific value. Dense, slow-burning wood provides the greatest heat.
Generally, dense timbers are found in dry climates at low elevations, and less dense timbers are found in wet climates at high elevations.
The drier the firewood, the better. Green wood is 20 percent heavier and bulkier than dry wood 8, but has only 40 percent of its heating-value. (Burning timber in its green state can also produce more hazardous emissions than when it is dry - ed.)
Firewood can take up to two years to dry, depending on species, piece, size and drying conditions. If wood is stored under cover, it can be dried to about 12 percent moisture-content, whereas 30 percent moisture is common for wood dried in the open air.
Drying guidelines:
FIREWOOD PRODUCTIVITY AND ANNUAL RAINFALL
| Annual Product'n & Usable Firewood (dry tonnes/ha.) | Annual Rainfall (millimetres) |
Spacing (metres) |
Rotation Length (years) |
| 300 | 5 - 7 mm | 11 - 15 | 0.5 - 1.5 |
| 500 | 3 - 5 mm | 9 - 13 | 1 - 3 |
| 700 | 2.3 - 3.5 mm | 7 - 11 | 3 - 8 |
| 900 | 2 - 3 mm | 5 - 10 | 5 - 15 |
| With Supplementary Water: (ie, irrigation or shallow groundwater) | 3 - 5 mm | 7 - 15 | 8 - 25 |
HEAT POTENTIAL OF COMMON FIREWOOD SPECIES
| Species | Heat Potential (%) |
| Grey Box | 100 |
| Grey/Red Ironbark | 97 |
| Red/Yellow Box | 91 |
| River Red Gum | 80 |
| Southern Blue Gum | 80 |
| Silvertop Ash | 75 |
| Messmate Stringybark | 68 |
| Manna Gum | 68 |
| Peppermints | 68 |
| Mountain Ash | 63 |
| Alpine Ash | 55 |
| Radiata Pine | 45 |
| Poplar | 45 |
1. See under Good Wood Groups, in the Directory.
2. See also Books, Firewood, in the Directory.
3. The Rainbow Power Company has available a burner which generates electicity from minimal amounts of sawdust. Its only apparent drawback may be the price. See Alternative Energy in the Directory.
4. Refer to Wood in Australia, by Keith Bootle.
5. See also Woodsmoke and the Art of Cleaner Burning, in Earth Garden no.95.
6. See under Government Departments, in the Directory.
7. See under Books, Journals.
8. See Wood and How to Dry It, in Books, Woodcrafting.