Moisture Content of Firewood Explained

Published On:
December 21, 2019

What does the moisture content mean?

Moisture content is an effective measure of how well the wood will burn. Soggy, unseasoned wood will smoke and cause your flu to become lined with tar and soot, reducing its effectiveness and also making it a very real chimney fire risk. Here at WoodShack, we guarantee that all our seasoned wood has a moisture content of less than 20%, so you can be assured of a hearty, roaring fire.

Why is it important to buy dry wood?

35%-45% of the weight of freshly felled wood is water and trying to burn it will produce steam rather than heat. Drying or “seasoning” reduces the moisture content of the wood. Wood should be seasoned before it is burned, and the moisture content reduced to at least 25%. The lower the moisture content, the better the wood will burn. As well as producing little heat, burning wood that has not been properly seasoned can result in tar deposits in the chimney and smoky, rather than clean burning fires.

Lighting a Fire with Dry Firewood is Best

It is important to use dry firewood when lighting a fire in order to get the most out of your firewood and your wood-burning stove. With dry firewood, you’ll get the best combustion. Keep the environment in mind when lighting a fire in your wood-burning stove – you must use dry firewood in order to avoid particle emissions.
Firewood is dry when its moisture content is lower than 18 %. The moisture content in firewood indicates the amount of water in the firewood expressed as a percentage of the firewood’s weight. A piece of firewood weighing 1 kilogram with a moisture content of 20 % contains 200 grams of water.

Why should you light a fire with dry firewood?

You should use dry firewood because it ensures you the best combustion and that you’ll get the most heat out your logs. The efficiency is much higher when you light a fire using dry firewood as opposed to using moist firewood.
If you use moist firewood, it is both damaging for the environment and often it will be uncomfortable for your neighbours because of the smoke generation that it will cause.

How to check whether your firewood is dry

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

  1. Add a little soap on one end of the log
  2. 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.