How-to guide
Firewood Moisture Content: What It Should Be and How to Test It
Firewood should have a moisture content of 20% or less before you burn it. That's the level set by the Ready to Burn scheme, and wood at that level lights easily, burns hot and makes little smoke. The only reliable way to check is with a moisture meter on a freshly split log, at room temperature.
The Logs Local team Kiln-dried logs from our yard in Keighley
In this guide
What do moisture readings mean?
| Reading | What it means | What to do |
|---|---|---|
| 20% or less | Dry. Ready to burn | Burn it, and keep it stored dry |
| 21% to 25% | Nearly there | Leave it to dry for longer before burning |
| Over 25% | Wet | Don't burn it yet. Split, stack and dry it |
Freshly felled wood can be around 50% water. Forest Research says green wood has about half the energy of well-seasoned wood, because so much heat goes into boiling off the water.
How do I test logs with a moisture meter?
These steps follow Woodsure's guidance.
- Bring three logs indoors. Take them from different parts of your store, such as the top, middle and bottom, and leave them to reach room temperature.
- Split each log down the middle. The outside of a log dries first, so a reading on the surface can look drier than the wood really is.
- Wipe the fresh face. Remove any dust or surface moisture.
- Press the pins in across the grain. Push them in firmly on the split face, away from knots, and take several readings at different spots.
- Average the results. Repeat for each log and take the average. That's the moisture content of your load.
Temperature affects the reading by roughly 1% for every 10°C away from room temperature, and frozen wood can't be tested, so don't test logs straight from a cold store in winter.
What if I don't have a moisture meter?
These signs help, but none is as reliable as a meter.
- Cracks across the ends of the log.
- Bark that is loose or comes away easily.
- Sound: two dry logs knocked together sound hollow; wet logs give a dull thud.
- Weight: dry logs feel light for their size.
- In the fire: wet wood hisses, steams, smokes and struggles to stay lit.
How do I dry wet logs?
- Split them. Forest Research recommends splitting logs to under 10 cm across so they dry faster.
- Stack them off the ground on bearers or pallets, in a sunny, windy spot.
- Cover the top, leave the sides open so rain stays off and air moves through.
- Give them time. Air drying to 20% can take two summers or more.
If you'd rather not wait, buy kiln dried logs. Ours are dried below 20% moisture and ready to burn when they arrive. See kiln dried vs seasoned logs.
Questions
Why does my meter give different readings on the same log?
Moisture isn't even through a log. The ends and outside dry first. That's why you split the log and average several readings.
Can kiln dried logs read above 20%?
Yes, if they've been stored somewhere damp or left in the rain. Store them under cover, and test them if you're not sure.
Is lower moisture always better?
Wood around 10% to 20% burns well. Very dry wood burns fast, so turn the stove's air down once the fire is established.
What does the law say about moisture?
In England, wood sold in volumes under 2 m³ must be certified Ready to Burn, which means 20% or less. See what is Ready to Burn?.
Back to the firewood buying guide.
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