Why season firewood?

Hi all!

How are we doing? We recently posted a little about our source of heating for our home, where we mentioned about seasoning firewood. Its something that we were aware of, but when we wrote the article we decided to look into the science behind why firewood needs to be seasoned. Allow us to share some of what we found out…

If you cut fresh timber it still has a lot of moisture in the form of sap – normally between 30 and 45% of the material of fresh wood is water. This high moisture content causes the fire to burn inefficiently as the heat produced is used to heat and evaporate the water rather than burning the wood and allowing heat to radiate out into the room. Ideally firewood needs to have a moisture content of around 20% to burn effectively.

The amount of moisture in fresh wood varies depending on the time of year. Over the winter while trees are dormant, the sap is not rising in the wood and therefore the moisture content of the wood is lower. It therefore makes more sense to use wood felled over the winter for your firewood, if possible. Once felled it’s better to saw and chop the wood into the size you’ll need for your fire straight away. This will help the wood to dry out more effectively – its a basic physics at work here with maximising the surface area of the wood and exposing more material to the atmosphere.

Once cut and chopped the logs should be stored them in a dry place, either in covered but open stores outside or in a shed of some kind. If you’re stacking them in walls, you should leave space between the walls of logs so that air can circulate and allow the timber to dry out. If you can raise the bottom layer of logs on something like an old pallet then so much the better.

We’ve looked into how you can tell when logs have reached this magical 20% water content. There’s a variety of devices available that give you a pretty good reading, and aren’t too expensive. At some point when we have sorted some other bits out we will invest in one of these. A cruder method is to look for small cracks forming in the ends of the logs where the wood is contracting as it drys.

Hope this has answered a few questions!


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