With the turn of seasons, we are already starting to see wood smoke curling up out of chimneys all over town. If you haven’t had a fire already, you may want to start checking your wood supplies before the first really cold snap. You should never burn wood that isn’t properly dried and has still got a high moisture content. It won’t burn very efficiently for starters, but it will also cause a build-up of soot in your fireplace and chimney that can be dangerous, and difficult to clean.
But what if you have logs left over from last winter that you are hoping to use? They could be fine if they have been stored properly, but if they have been exposed to the elements or have been left directly on the ground, then they could have absorbed enough moisture to make them unsuitable to burn for a while. One way to make sure your logs are dry enough is to use a moisture meter. This is a small hand-held device, usually with two metal prongs that you insert into your wood to give a reading of its moisture content. Building surveyors use the same device to check for damp in buildings. They work by passing a small electrical current between the two prongs and as water is a much better conductor of electricity than wood, the device will be able to calculate the moisture content. The digital display will give you a percentage reading that tells you how much of the wood’s weight is made of moisture.
To give you a comparison, a piece of green oak trimmed directly from a living tree will have a moisture content of around 50-55%. If left in a warm dry place, this will slowly reduce over many months to the point where it becomes suitable to burn i.e. with a moisture content below 20%. You can get this reading even lower by drying logs in a high temperature kiln, which can reduce the moisture content to as little as 10%.
If you are using the two-prong type of moisture meter for logs, you should bear in mind that wood dries from the outside inwards. If you get a reading of 20% on the exterior of the log, then the inside could be a lot higher. To get the most accurate reading you should split a couple of logs and take multiple readings from the centre of each piece. Alternatively, you could opt for one the more expensive meters that use electromagnetic waves to scan the wood for moisture. If you have spent several thousand pounds on a fireplace or wood burner, then it is a small additional cost to ensure that you are not burning wood that will damage your flue and chimney over time. But if this sounds like a whole lot of hassle when you just want to be sitting by a cosy fire, you could always err on the side of caution and simply stock up on some good quality kiln dried hardwood logs or heat logs, which are guaranteed to have a very low moisture content.
So, in answer to the original question ‘Do I need to buy a wood moisture meter?’ then the answer is probably no if you are only planning on using high quality logs from a reputable supplier where you can be sure the moisture level is below 20%, but a definite yes if you are burning wood that you have stored yourself or have bought from a less than reliable source.