The Importance of Understanding Moisture Content When Burning Woodfuel

As winter approaches, and we come to rely more on our wood The Importance of Understanding Moisture Content When Burning Woodfuelburning boilers and stoves, we must make sure the fuel we are burning is as efficient and environmentally friendly as it can be. The key to this is ensuring that we are burning high quality wood with low moisture content. So, to help installers, retailers and consumers, Woodsure – the UK’s only woodfuel quality assurance scheme – has put together everything you need to know about the moisture content in different types of woodfuel and what this means for different appliances…

What is moisture content?
Moisture content is one of the key parameters used to classify woodfuel, as it directly influences the calorific value, or energy, within wood. The moisture content of a piece of wood is a measure of the relative weight of water and weight of solid wood. We know that water does not burn, therefore the more water within wood the more difficult it is to burn.

How does moisture content affect burning and efficiency?
The Importance of Understanding Moisture Content When Burning WoodfuelAny water within woodfuel has to evaporate before it will burn, which will reduce the net energy released as useful heat, as shown below. Any appliance that is not designed to burn wetter fuel may take longer to heat up and may never reach optimum efficiency. While wood with high moisture content will release a lot of steam, this is not heat that can be felt in the home or other buildings. Logs that aren’t dry when burnt will also cause a fire that smoulders and creates lots of tars and smoke. If left unattended, this can cause chimney fires and so you will be required to have your chimney swept more regularly.

Woodfuel with less than 20% moisture content is over two times more efficient than fuel with over 45% moisture content. As the moisture decreases, the energy within the wood increases, as a result fuel with less water embedded can burn for longer and more efficiently, meaning less fuel is required to produce the same amount of heat.


What is the ideal moisture content for your appliance?
The ideal level of moisture content varies depending on what appliance is being used. Moisture content is likely to vary between logs with different size, species, cracks and where they have been stored. Moisture content from freshly felled timber is between 45-60% but by naturally seasoning the timber this can be brought down to 25% over a period of 6 to 18 months – dependent on where you are in the UK and the storage conditions. While different appliances can operate with a different level of moisture content dependent on its use. Non-domestic boilers like Binder can burn woodfuel with up to 45% moisture, for wood burning stoves and boilers used in the everyday home, the moisture content of the fuel should be below 20%.

Woodsure’s tips for seasoning wood

Cut firewood to the right length for the stove or boiler before seasoning

To dry logs, store them in a sunny, well aired space for one or two summers, ensuring fuel is not exposed to rain or snow

 Stack wood in early spring for use the following winter

Radial cracks and bark which comes off easily are signs that the wood has been well-seasoned


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