How to check your firewood logs are dry enough using a moisture meter

August 10, 2021

Almost everyone who sells firewood says their logs are seasoned and ready to burn. Sometimes they are.

Under current legislation, there are two approved ways to buy firewood for your stove. Either you buy regular quantities of logs that must be certified ‘Ready to Burn‘ (i.e. described as below 20% moisture, from an approved supplier) or you buy in bulk – over two cubic metres at a time – to season at home.

Whether or not your ‘ready-to-burn’ logs arrive as described is another question. Woodsure can’t examine every batch; in practice, a lot is going to depend on trust. From our perspective, though perhaps not Woodsure’s, that’s a good thing. We think log supply should, wherever possible, be a local matter, for reasons rational, environmental and social.

If you want to establish the state of your logs, you can do so with a moisture meter, but there’s a knack to deploying one properly.

But you always want to be sure of what you’re buying. And certainly sure of what you’re about to burn. Give or take a few points, 20% is roughly considered the benchmark for a dry log. If you’re a hoary-handed woodsperson, you’ll know if a log is right just by picking it up, by the sound made by knocking two together or even just by looking at one. For everyone else, a moisture meter is a good investment.

How to use your moisture meter

Read the instructions! Put the batteries in. Press the ON button. Make sure the digital display lights up. Push the prongs into the side of the log. Here we get a reading of 13%. This is not the moisture content of your log! Read on…

Testing outside edge

Flipping the same log over gave us a reading of 14% on the other side.

the flip side

This was a kiln-dried log (incidentally, a ridiculously energy-intensive way of seasoning that the sun and wind will do for free), and these are the kind of readings you would hope to get from one. But first appearances can be deceptive. You need to get beyond surface impressions.

For that, you’ll need to split the log. (If you’re not used to handling a hatchet, take care. Even for experienced axe-wielders, it’s all too easy to lop off a thumb or forefinger.) Plunge the prongs into one of the freshly-cut surfaces.

after the log is split

In this instance, the reading was 35%. Although the actual ‘moisture content’ of the log would be perfectly represented by averaging readings from various points on the log, an internal reading like this of 35% is far too high. For illustration, 35% is the approximate moisture content of freshly-felled ash, and the bark of a live tree will often return a reading of under 20%.

This log was simply not dry enough to burn as a fuel.

35% moisture

So if you want to check your wood, pick up one of our moisture meters, split your logs and check them – either when you buy them or before you burn them.

Even if you’re disappointed, though, and have bought a batch of damp logs, there is good news. Time may not heal all wounds, but it can dry all wood. Make sure your wood store is shielded from the rain but well-ventilated, and most semi-seasoned logs will be ready for the next winter after a couple of months (freshly-felled logs are a different matter, and will need anywhere from six summer-spanning months to two years to season properly, depending on species and storage conditions).

For more information on the rules, and to find certified local suppliers, you can visit Woodsure.

Some might see the new rules as infantilising government overreach (coincidentally rewarding large-scale operators and the Treasury, while putting smaller concerns out of business), others as insufficient to ensure clear air (because it still doesn’t stop ‘consumers’ burning poor fuel if they’re able to acquire it). All critics might question how effectively the rules can, and will, be enforced. All these criticisms are valid. That doesn’t dispel the purported purpose of the legislation, which is to discourage the supply of wet logs. It will probably help in that regard.

As ever, we would encourage our customers to only ever burn dry wood and to burn it properly, ensuring sufficient air in their stoves for clean combustion, and to build as good a stock of logs as possible, preferably two years’ worth or more. If you can, buy your firewood green, locally and in bulk and season it yourself.

It’s literally money in the bank.