It is important to know what the moisture content is of any wood you are buying to burn. The more water contained in the wood, the less heat will be released to warm your home as that heat will be used to evaporate the water from the wood. This will also create unwanted steam which will reduce the level of heat even further. Therefore, a log that is heavy may not burn as well as a lighter log, as it may contain a lot more water. To burn as efficiently as possible, wood needs to be dry or seasoned before it is burned.
Freshly harvested wood will have a moisture content of over 50%, but the industry quality standard for firewood has been set at 25% (wet basis) or less. Drying wood fuel to around 20 to 25% moisture content can almost double its calorific value and therefore heat output. To ensure you get the best out of wood fuel we recommend using a moisture meter to test firewood, placing it along a freshly split surface of a log and taking an average from several points. A good wood fuel supplier will always know the moisture content of their product and be able to demonstrate it with a meter.
As well as being inefficient, wet wood can also damage your system as it will cause tar to build up in your stove and flue – this is ultimately what causes chimney fires. Have you ever experienced your stove glass turning black? If so, it is almost certainly because your wood is not dry enough. The correct moisture content in wood will ensure a clean efficient burn and a clean chimney, although even with dry wood, you still need to have your chimney swept at least once a year. Some log suppliers now use kilns to speed up the drying process and provide a more consistent product. These kilns can even be fired with wood waste or use solar heat to dry wood quickly. Ask your supplier how the wood was dried and using what fuel.