When wood is burned, it is usually best to dry it first in order to reduce the moisture content. The type of firewood burnt determines how well your woodburner, log burner or multi-fuel stove will perform. Seasoned and kiln dried are two of the most common types of firewood and it is important to understand the differences between these in order to maximise the efficiency of your stove:
These are logs that you may have partially dried out yourself or have been sold pre-dried by the manufacturer or supplier. Seasoned logs typically contain a moisture content of between 25% – 40%. Because of this, they have a heat output of around 3kWh per kg.
Kiln Dried Logs
This type of firewood has been professionally dried in a kiln before being sold and contains less than 20% moisture. Kiln dried logs typically produce a heat output in excess of 4.5kWh per kg.
Wood that has been collected, often from the local area, could have as much as 90% moisture within it. The resulting heat output is as little as 1kWh per kg. There are many ways to dry out wood, the most effective of which is by drying it in a type of kiln.
As its name implies, kiln dried firewood is wood that has been dried in a kiln. The kiln effectively bakes the firewood, forcing out the moisture that is naturally present. It takes much less time to kiln dry wood than it does to naturally prepare it. Kiln dried wood is naturally seasoned, easy to use, and burns efficiently.
Traditional seasoning methods require between 6 – 12 months of storage before the logs have a low enough moisture content to be used. If not, the wood is considered to be “green,” which alludes to the fact that it was recently living. Owing to its very high moisture content, green wood will not burn well. It generates a huge amount of smoke and will cause the fire to sputter, spit and emit black smoke.Because this undried wood does not burn efficiently, not only does it generate a lower heat output than kiln dried or seasoned logs but its combustion produces a range of by-products that can clog your chimney or flue. Burning unseasoned wood leaves a debris that can pose a potential fire hazard. In addition, unseasoned wood creates pollutants that compromise air quality. Wood must be dry so that it can burn more efficiently and cleanly. To reduce the amount of moisture absorbed from the air, dried wood should be stored in a covered or enclosed space.
As a rule of thumb, the lower the moisture content in your firewood, the more efficient it is. With this in mind, kiln dried logs are the best available and make the perfect choice for woodburners, stoves and open fires as well as firepits, pizza ovens and chimineas.
What are the benefits of using kiln dried logs?
• Generates greater heat output – Kiln dried logs typically produce a heat output in excess of 4.5kWh per kg. This is significantly higher than that of seasoned logs (typically around 3kWh per kg), or unseasoned wood (typically less than 1kWh per kg)
• Fuel efficiency – In simple terms, kiln dried logs burn hotter than seasoned logs or unseasoned logs. With less moisture contained in the kiln dried wood, less energy is required to burn off residual moisture and therefore more energy converts into heat.
• More economical – As you might expect, wood with a higher moisture content is cheaper than kiln dried firewood. As an average, seasoned logs cost around £125 per cubic metre whereas Kiln dried logs cost around about £140 per cubic metre. However, given their greater efficiency and heat output it is true to say that kiln dried logs will burn for longer and give out more heat making them overall more economical. Using cheaper seasoned or unseasoned wood is often a false economy.
• Minimises stove and flue problems – the reduced moisture content found within kiln dried logs means that they burn easily and evenly. The drying process ensures that the sap will not spit and snap when the log burns. Black smoke, pollutants, soot and other deposits are therefore minimised and they will not cause stove and flue problems. For this reason, many stove manufacturers recommend the use of kiln dried logs and in some cases the burning of unseasoned wood can even invalidate your warranty or product guarantee.
• Easy to transport and store – since the weight of a log can drop by as much as half when it is properly dried, kiln dried logs are easily portable and no not require a huge amount of strength to load into the fireplace. Since kiln dried logs are dry and often supplied in nets, no complicated or messy transportation or storage is required.
• No insects or fungi – as the kiln drying process kills insects and fungi, there is no risk of introducing these unwanted visitors into your home.
In summary, kiln dried wood makes the best firewood. It will light easily, burn cleanly and provide maximum heat output. Your stove glass will not go black and the burn of your chimney or flue will be clean and therefore not cause excess soot or deposits. The difference between using kiln dried logs compared to seasoned or unseasoned wood is not to be underestimated and cannot be truly appreciated until you try it.