What Moisture Content Should Firewood Be?

Q: Why are your meter readings odd?

Very high readings near the bark. Rain-soaked surfaces or sapwood can cause this. Split the log and measure on the fresh face.Readings drop a lot from end to middle. End grain dries fastest, so always measure in the middle of the split face.Readings vary between logs. That is normal. Average several logs and resample the wettest part of the stack.Readings are steady but unexpectedly low. Check that the battery is good and the species setting is correct. Many meters include a check cap or reference contacts.

Stacked split firewood logs drying in a woodpile

Short answer: Firewood should be at 20 % moisture content or lower before you burn it. In England, wood sold in small quantities must meet that limit by law.

Why does moisture content matter?

Freshly felled timber can be half water by weight. Burning wet wood wastes energy, because the fire has to boil that water off before it gives out useful heat. It also produces more smoke and fine particles and leaves tar deposits in flues and chimneys. Dry wood lights more easily, burns hotter and cleaner, and gives you more heat from each log.

What does UK law say?

In England, the Air Quality (Domestic Solid Fuels Standards) (England) Regulations 2020 restrict the sale of wet wood for domestic burning. GOV.UK guidance sets out the main points:

Wood sold in units under 2 m³ must have a moisture content of 20 % or less. That covers bags, nets and crates.
It must be certified under the Ready to Burn scheme and carry the scheme's label.
Wood sold wet in larger volumes must come with advice on how to dry it before use.

The Welsh, Scottish and Northern Irish governments set their own rules, so check locally if you sell outside England. The 20 % figure is still widely used as the benchmark for well-seasoned logs.

How do you measure firewood moisture correctly?

The Ready to Burn scheme explains how to use a pin-type moisture meter. In short, the outside of a log dries faster than the core, so a reading from the surface can be misleading.

Freshly split firewood showing the pale inner wood face — Always test the freshly split inner face, not the bark or the sawn end.

Choose a typical log. Take one from the middle of the stack, not the top.
Split it. Split the log in half and measure straight away on the freshly split face.
Insert the pins along the grain. Push them into the centre of the split face, parallel with the grain, unless your meter tells you otherwise. A pin-type meter such as the TASI TA661B is made for this.
Push both pins into the centre of the split face, along the grain.
Take several readings. Test three or more logs and use the average.
Set the species if your meter allows it. Different densities affect the reading. Some meters have hardwood and softwood modes.
Watch the temperature. Very cold or frozen logs give low readings, so let a sample warm up indoors for a short while first.

Most handheld meters show moisture on a wet basis or a dry basis. Check which one yours uses and compare like with like.

How long does seasoning take?

It depends on species, log size, airflow and the weather. As a rough guide:

Neat stack of grey, seasoned split firewood — Split, stacked and covered logs dry faster, but measure before you burn.

Split logs dry faster. More surface area is exposed.
Stacks need airflow and a roof. Keep them off the ground, cover the top and leave the sides open.
Softwoods usually dry sooner than dense hardwoods such as oak.
Kiln drying reaches the target in days rather than seasons.

Don't rely on the calendar. Measure before you burn or sell, because some logs can still be over the limit after a summer outdoors.

What about timber for building and joinery?

Firewood is a separate case. Timber used indoors needs to match the moisture level it will settle at in service, or it will shrink, twist or open at the joints. Forest Research guidance gives approximate in-service moisture contents: roughly 10 to 16 % in unheated buildings, 9 to 13 % in heated rooms between 12 and 21 °C, and 6 to 10 % in rooms kept above 21 °C. A meter with species correction is very useful for joinery and flooring work.

Why are your meter readings odd?

Very high readings near the bark. Rain-soaked surfaces or sapwood can cause this. Split the log and measure on the fresh face.
Readings drop a lot from end to middle. End grain dries fastest, so always measure in the middle of the split face.
Readings vary between logs. That is normal. Average several logs and resample the wettest part of the stack.
Readings are steady but unexpectedly low. Check that the battery is good and the species setting is correct. Many meters include a check cap or reference contacts.

FAQ

Is 25 % acceptable for burning? It will burn, but less efficiently and with more smoke. Aim for 20 % or below.

Do I need certification to sell logs? In England, wood sold in units under 2 m³ must be certified as Ready to Burn. See the GOV.UK guidance for details.

Can a pinless meter test firewood? Pinless meters work best on flat, planed surfaces. A pinless damp meter is better suited to comparing dry and damp areas in walls, floors and finished wood. A pin meter on a freshly split face is the method the Ready to Burn scheme describes.

Do wood briquettes count? Manufactured solid fuels have separate requirements under the same regulations.

Sources

GOV.UK, "Selling wood for domestic use in England": https://www.gov.uk/guidance/selling-wood-for-domestic-use-in-england
The Air Quality (Domestic Solid Fuels Standards) (England) Regulations 2020: https://www.legislation.gov.uk/ukdsi/2020/9780348210194/schedule/2
Ready to Burn, "Measuring firewood moisture content": https://www.readytoburn.org/consumers/advice-hub/measuring-firewood-moisture-content/
Forest Research, timber moisture content guidance (in-service moisture levels): https://cdn.forestresearch.gov.uk/2016/03/fcrp025.pdf

Related products: Moisture Meters & Refractometers