A Guide to Check Log's Moist Content

Published On:
February 24, 2020

Before you start reading about possible solutions, you might want to understand...

How Do You Remove Moisture From Wood?

Kiln Drying
Freshly cut wood has a lot of moisture in it. Eventually, this internal moisture will evaporate by itself. However, kiln drying is used to speed up the process. Some of the unfinished wood you see on the market has been kiln-dried to reduce its water moisture content to around 8% so that it won’t suffer from moisture-related defects like warping and buckling. However, many building materials may have been dried down to about 15% moisture content.

But, that’s not the end of the story…

Wood moisture content is always varying. It’s never constant. Wood – freshly cut or kiln-dried – is always interacting with environmental moisture. Therefore, just because the wood is kiln-dried doesn’t mean it has lost the ability to absorb moisture. It will continue to absorb and release moisture until it comes into balance with the surrounding air.

How to check if your firewood is dry

There are different methods for checking whether your firewood is dry enough to light a fire with.
Oven Dry Testing

Oven dry testing is the oldest method for measuring the moisture content of wood. The process is time-consuming but produces accurate results if followed correctly. Here’s how it works…

The wood sample being tested is dried in a special oven or kiln and its weight periodically checked. Once the wood sample’s weight stops changing, its weight is compared to what it was before the drying process began. This weight difference is then used to calculate the wood’s original moisture content.

While oven-dry testing, if followed correctly, offers accurate results, there are a few drawbacks:

  • It takes a long time – We’re talking about hours. The oven drying process must be done slowly or the wood could burn and the test results will be worthless.
  • It will render the wood unusable – It often happens that oven drying over dries the wood to the point where it’s unusable.
  • It requires a special oven or kiln – Most hobbyists who work with wood don’t have an oven that’s capable of producing accurate results.

Soap test – blow on the firewood
It is easy to test your firewood to see if it is dry – you can use regular washing-up soap
How to do it:

  • Add a little soap on one end of the log
  • Put your mouth near the other end and blow through the log

Your firewood is dry if bubbles appear. This happens because there are some channels inside the log which transport water. When the wood has been cut and dried, the water disappears, and air can pass through when you blow.

Use the sound test
You can also test the dryness of your firewood by banging together two pieces of wood. Your firewood is dry when the sound is hard and ringing. Moist firewood has a dull sound.
Be aware of pitfalls when it comes to the sound test. In frosty weather and when the temperature is below 0° Celsius, fresh wood can give off a high and ringing sound even if the wood is not yet dry. Remember that the sound test only provides you with a superficial impression of the condition of the wood. It won’t always disclose whether the wood is dry at the core.

Look at the firewood
Your intuition is also a useful tool when it comes to assessing the moisture content of the firewood. Below is a dry firewood checklist: Firewood must be…

  • Dry
  • Clean
  • Hard
  • Having dry cracks on the ends
  • Without mould and fungi
  • The smell of resin and juice disappears as the wood dries
  • Having clearly visible growth rings
  • Light in colour. Sun exposure makes the wood yellow and old wood turns greyish. Often the bark will separate from the wood.

If your firewood matches the criteria, it’s a sign that your firewood is dry enough for firing in your wood-burning stove.

Use a wood moisture meter
You can also use a wood moisture meter for measuring the moisture content of your firewood. With a wood moisture meter, you’ll get the most precise information on the moisture content in your firewood.