Kiln Dried Firewood - The Natural Energy Resource
Kiln dried firewood is becoming the popular choice for many Consumers, as we become more environmentally aware of renewable energy. Its many benefits include, higher heat output, more fuel efficient and therefore economical and minimises problems with your stove and flue. Both hardwood and softwood are kiln dried, hardwood is a deciduous slow growing broadleaf of high density wood producing a slower steady heat output. Softwood is fast growing evergreen conifers with low density wood and will give high heat output with a quicker burn.
Kiln dried versus seasoned logs
When a tree is felled it will contain between 65 – 90% of water depending on the species. Felled trees will be stored in the forest for up to two years in their complete form and this is known as seasoning the wood, there is actually very little drying of the wood as bark has evolved to keep moisture in!!!! For seasoning to be effective the trees have to be cut into logs and split, stored in a dry area with plenty of air flow. Kiln dried wood goes through a different process, it will be felled and then cut into logs and split and then put into a kiln to bring the moisture to less than 22%. So basically when you put fresh or seasoned wood onto a fire, it uses heat from the fire to dry it before it can burn it, kiln dried wood burns straight away at a constant higher temperature and works out to be 33% more efficient than seasoned wood.
22% Moisture in Kiln Dried Firewood
Common wood used for kiln dried firewood are Ash and Birch this is because they have a low starting moisture content making them easier to dry. Denser woods are obviously also dried but it is a longer process. Freshly cut wood has a very high moisture content. As much as 60% of the weight of a tree is water. At least some of this water must be removed before trying to use it as firewood. There are many pitfalls that can occur from burning wood that is not dried to below 25% moisture content. This is often referred to as "green" wood and the effective available heat is much less, not just because there is less wood fibres in each pound of wood put in the wood burner, but that a good percentage of that heat must be used to evaporate all that water before those wood fibres can burn. Another very important consequence of burning green wood is that the presence of all that moisture tends to keep "putting out" the fire, it’s never a good sign when your fire is hissing, and therefore making it burn very poorly, which tends to produce a lot of creosote and pollution. Generally, one way the drying is accomplished is by seasoning it. Firewood is cut to length and then seasoned (dried) in a stack, with air being able to get to it, for at least 9 months before burning. The natural 60%-70% moisture content must be reduced to about 20% to burn well. The wood doesn't lose much moisture through the bark, the moisture is most effectively removed through the cut cells at the ends of each piece. That's why logs which have lain in the woods for years may still have a lot of moisture and may not burn well until they have been cut and split and then stacked and covered with a good airflow but even that will not bring the moisture content down to 22%. Generally it is sold that wood that has been seasoned for 2 years will be drier than 1 year seasoned wood but it is thought that there is no further drying occurs beyond 9 months. The only effective way to bring wood moisture level down to 22% is through Kiln drying it. This process can be monitored and controlled to reach the correct level which produces the optimum fuel for the fire.
Wood Burning Stoves and Multi Fuel Stoves
All manufacturers recommend that you only burn kiln dried firewood in your stove. Burning wet or seasoned wood can damage your stove or flu which will be costly to repair. To have your stove running to maximum efficiency you need the best performance from what you burn, burning kiln dried firewood produces two thirds more heat output than wet wood and a third more than seasoned wood.
Burning kiln dried firewood is better for the environment, you don’t need to burn as much for a start cutting down on labour, transport and storage. When wood has a higher water content the gases in the wood can’t ignite and escape up the chimney which is further heat wasted and also causing excess soot and tar. Wood is also part of the carbon/carbon neutral cycle. The fuels produce CO2; trees absorb CO2 and store it as carbon which makes up half the weight of the tree. When the wood is burned it releases only the same amount back into the atmosphere, exactly the same as if the tree was left to rot.