July 20, 2011
How kiln dried firewood is made
Kiln drying involves the introduction of heat to reduce the water content of the firewood. Heat is traditionally provided by gas or electric heating, by steam heat exchangers or via solar power. Most log drying kilns operate at temperatures of up to 110 degrees Celsius, with typical log drying times of 1-2 weeks. A kiln schedule is used to determine the exact time and temperature required to effectively dry the firewood, based on the type of wood involved.
Traditional kilns are constructed of brick masonry or a hollow cement structure and the wood is stacked in chambers to optimise the air flow around the logs and therefore improve drying. Air circulation is critical, to carry evaporated moisture away from the wood and this is often assisted by fans in the kiln. Dehumidification systems are also sometimes used to maintain the humidity of the kiln at a constant level during drying. In dehumidifying kilns, water vapour is condensed off in the dehumidifier and removed as a liquid.
During the kiln drying process, insects and mould are killed off, meaning that kiln dried logs are cleaner, lighter and better burning than air dried firewood. To determine if the kiln drying process has been effective, there are three practical methods of measuring moisture in wood.
- Physically weighing the timber before and after drying it and calculating the moisture content.
- Using a pin type meter which measures the electrical resistance of the timber.
- Using a meter that uses electro-magnetic technology to measure moisture.
Logs which have been kiln dried produce the highest possible heat output when burned due to a much lower moisture content (kiln dried logs have less than 20% moisture, whilst the driest seasoned logs usually still have 30% moisture). The more moisture present in the logs, the more heat energy is wasted in water evaporation when the logs are burned.
For the best selection of kiln dried firewood including free delivery thoughout the UK, visit Logs Direct. Logs Direct are one of the main kiln dried firewood specialists in the UK with their own kiln drying, log processing and distribution facilities. Because they are a direct supplier, they can offer kiln dried wood at a far lower cost than most firewood distributors.
I have just read this article on kiln dried logs and must say its absolute nonsense air dried have no more or less moisture than kiln dried, a seasoned log which is under 25% moisture is seasoned whether air dried or kiln dried, we personally air dry all our timber and it measures 11% to 18% with mixed hardwood including oak with 8-12 months drying time. I have also checked 2 diff sources of kiln dried logs and they measured 22 and 26% moisture so this article is totally misleading and inaccurate but good for selling logs to gullible people at a 40% price premium. you also haven’t included that when the logs are removed from the kiln they must be stored in a humidity controlled area or they will reabsorb moisture to the same content as air dried logs.