Burn drier logs. Build with stable timber.
Check moisture before you burn, buy, store or machine wood. Tap a problem to jump to it.
Wet logs, smoky fires and blackened stove glass
Why it happens
Freshly cut wood holds a lot of water. Burning it uses energy to boil that water off, so the fire runs cool, smokes and leaves tar on the glass and in the flue.
How to tell it apart
Thick dark smoke or stove glass that blackens quickly usually means wet wood or too little air. Open the air control fully and burn a few logs you know are dry. If the glass stays clean, the problem was the wood. If it still blackens, check the air supply and flue, and have the stove and chimney checked by a competent installer or sweep.
How to test
- Split a log from the middle of the pile. The outside dries first, so the bark and outer face read too low.
- Set the meter to the right wood species or group, if it has that setting.
- Let logs brought in from a cold store reach room temperature first, or use the meter's temperature correction.
- Push the pins into the freshly split face, along the grain.
- Take at least 3 readings per log and use the average. Test 3 or more logs.
A pin meter such as the TASI TA661B is made for this.
Good and bad readings
| Log moisture content | What it means |
|---|---|
| 20% or less | Ready to burn |
| More than 20% | Too wet: keep drying |
Source: GOV.UK, Selling wood for domestic use in England ("Ready to Burn" wood has a moisture content of 20% or less) and the statutory customer notice ("measure a freshly split surface").
What next
If a log reads over 20%, don't burn it yet. The government notice says to dry wood "in a sunny, well-aired space for at least two years, keeping rain off in the winter". Stack it off the ground, cover the top only and leave the sides open so air moves through. Re-test monthly; burn once readings stay at 20% or below.
Common mistakes
Measuring the bark or outer face; one reading per log; testing cold logs straight from outside; blaming the stove before testing the wood.
Instrument for this step
TASI TA661B Pin Wood Moisture Meter for Firewood & Logs, 0-54.8%, 7 Materials, Damp Meter£30.99
Buying firewood
Why it happens
"Seasoned" is not a legal term. Logs can also get wet again in storage or on delivery.
How to tell it apart
Deep radial cracks in the end grain and loose bark suggest seasoned wood, but they are not proof. Only a reading tells you.
How to test
- Pick 3 logs from different parts of the load.
- Split each one and measure the fresh face, as in the steps above (at least 3 readings per log).
- Compare the average with the 20% limit.
Good and bad readings
| Load | What the rules say |
|---|---|
| Less than 2 m³ (bags, small loads) | Must be certified Ready to Burn: 20% or less, with the logo, supplier name and certificate number |
| 2 m³ or more | No certificate needed, but the seller must give you a notice saying not to burn it until it is 20% or less |
Source: GOV.UK, Selling wood for domestic use in England.
What next
If Ready to Burn wood reads over 20%, tell the seller first and keep your readings and photos. If that doesn't resolve it, contact Woodsure, which runs the scheme and can sample and test the fuel. Local authorities enforce the rules, so you can also report it to your council's Trading Standards team.
Common mistakes
Judging by weight or colour; testing only the logs on top; not checking the certificate number on the bag.
Seasoning progress
Why it happens
Logs dry mostly from the ends and split faces. A stack that is wrapped up, touching the ground or in shade dries slowly or not at all.
How to tell it apart
If readings stop falling, the store is the problem, not the wood: look for a damp base, a fully covered stack or no wind through it.
How to test
- Mark a few sample logs at different heights in the stack.
- Every month, split a sample and measure as above.
- Write the readings down so you can see the trend.
What next
Burn once samples stay at 20% or less. If readings stall, raise the stack on rails or pallets, uncover the sides and keep only the top covered.
Common mistakes
Covering the whole stack with a tarp; stacking against a wall; testing only the logs at the top.
Timber movement
Why it happens
Wood swells and shrinks as its moisture content changes. Below about 25–30% (the fibre saturation point) it moves across the grain, so boards cup and joints open.
How to tell it apart
Gaps that open in winter and close in summer are seasonal movement. Cupping on one face only usually means one side is wetter, often from a damp floor or wall.
How to test
- Let boards acclimatise in the room where they will be used.
- Set the meter's species setting and let cold timber reach room temperature.
- Take at least 3 readings along each board and on several boards.
A pinless meter such as the QT700I leaves no marks on finished timber.
Good and bad readings
| Internal joinery (BS EN 942) | Average moisture content in service |
|---|---|
| Buildings with heating | 9%–13% |
| Unheated buildings | 12%–16% |
| External joinery | 12%–19% |
Source: TRADA WIS 4-14, Moisture in timber, which also says tangential shrinkage is roughly 1% for every 3%–5% change in moisture content, and that no single reading should exceed the maximum average by more than 3%.
What next
Work or fit timber once its readings match the range for where it will be used. If you can't get there, ask your timber supplier or TRADA for advice on the species.
Common mistakes
Wrong species setting; one reading per board; measuring timber straight from a cold van.
Before fitting floors and joinery
Why it happens
Wood fitted while wetter than the room it goes into shrinks later; drier wood fitted into a damp building swells and can buckle.
How to tell it apart
Buckling floors often point to moisture from below (screed or subfloor); gapping points to wood that was too wet when fitted or a very dry room.
How to test
- Measure the boards in the room, after acclimatising, with the species set and at least 3 readings per board.
- Check that wet trades have finished and the heating is running at normal levels.
- Check the subfloor or wall too. Concrete screeds need a different test, so follow the flooring maker's method.
Good and bad readings
TRADA advises installing flooring and joinery only once the building has dried out and temperature and humidity are at the levels expected in service (TRADA WIS 4-14). We could not find a publicly available figure from BS 8201 (wood flooring) for specific floors, so for flooring moisture limits ask the flooring manufacturer, who sets the limits for their warranty, or TRADA.
What next
If readings are outside the maker's limits, wait, run heating and dehumidifiers, and re-test.
Common mistakes
Fitting straight from delivery; ignoring the subfloor; using a wood meter on concrete.
FAQs
Pin or pinless meter?
A pin meter is best for logs because it reads inside a freshly split face. A pinless meter is quicker on finished boards and leaves no marks.
Where should I measure a log?
On a freshly split face, not on the bark or outer surface, with at least 3 readings per log.
Can I get a VAT invoice?
Yes. All prices include VAT and VAT invoices are available.
Need help choosing?
Contact us and tell us what you need to measure.
Photo credits: Split a log, test the fresh face: photo by Øyvind Holmstad, CC BY-SA 4.0, Wikimedia Commons, Klyvøksa.jpg (https://commons.wikimedia.org/wiki/File:Klyv%C3%B8ksa.jpg); Seasoning progress: photo by Asurnipal, CC BY-SA 4.0, Wikimedia Commons, Klaus-Orsanka-Stack of firewood-01ASD.jpg (https://commons.wikimedia.org/wiki/File:Klaus-Orsanka-Stack_of_firewood-01ASD.jpg)