If you’ve ever struggled to get a fire going or wondered why some logs burn hotter than others, the answer almost always comes down to one thing — moisture content. It’s the most important factor in how well your firewood performs.
In this guide, we’ll explain what moisture content really means, how it affects your fire, and why buying properly dried logs is essential if you want clean, efficient heat.
What is moisture content?
Moisture content is the percentage of water still inside the wood when you burn it. Freshly cut logs can have a moisture content of 50% or more, meaning half the weight of that log is water. Burning that kind of wood is inefficient, smoky, and bad for your stove.
To burn cleanly and safely, firewood needs to be dried — either naturally (seasoned) or in a kiln — to reduce the moisture content to an acceptable level.
What is the ideal moisture level?
The UK’s “Ready to Burn” standard, introduced by Defra and certified by Woodsure, requires firewood sold in small volumes to be below 20% moisture. This ensures the logs burn safely and emit fewer pollutants.
But for maximum efficiency, logs should be even drier. According to HETAS and Forestry Commission UK data, firewood with moisture content below 15% burns hotter and cleaner than wood closer to the 20% mark.
That’s why at The Logsmith, we kiln dry all of our hardwood logs to under 15% — for better performance and more consistent results.
How does moisture affect heat output?
When you burn a log, energy is used first to evaporate any water in the wood before it can start generating heat. The wetter the log, the more energy is wasted.
Here’s how energy output compares based on moisture content:
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Logs with 7–15% moisture: 4,700–5,000 kilowatt-hours (kWh) per tonne
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Logs with 15–18% moisture: 4,400–4,700 kWh per tonne
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Seasoned logs with 25–40% moisture: 2,300–3,500 kWh per tonne
(Source: logsforsale.co.uk, HETAS, Heritage Products, Forestry Commission UK)
That means wood with under 15% moisture gives you up to twice the usable heat compared to poorly seasoned logs.
The impact on air quality and your stove
Burning damp wood doesn’t just give off less heat — it produces more smoke, more soot, and more harmful particulates. This can lead to tar build-up in your flue, higher risk of chimney fires, and poor air quality inside your home.
If you’re using a woodburner in a smoke control area, moisture matters even more. DEFRA-approved stoves rely on dry wood to maintain clean combustion and stay within emissions limits.
How can you tell if your logs are dry enough?
There are a few reliable ways to check:
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Look for the Ready to Burn logo (for moisture under 20%)
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Check the ends of the log — dry wood is often cracked and lighter in colour
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Use a moisture meter — ideal for firewood stored at home
The Logsmith only supplies logs that are ultra kiln dried and tested to below 15% moisture content before delivery. That way, you know every log you burn is clean, safe and efficient.