How dry does wood need to be for burning?
The Wood Guide · Reference
ReferenceHow dry should firewood be?
Below twenty per cent moisture. Above that, you spend part of your energy on evaporating water — and the rest goes up the chimney as smoke.
- Maximum 20 per cent
- 1 to 2 years of drying
- Measure with a moisture meter
Fresh wood is half water
Freshly felled wood contains 40 to 60 per cent moisture. To burn well it needs to be below twenty per cent — and that water has to evaporate before the wood can burn.
Click a chapter or use the arrows · schematic drawings; flame size follows the description on this page.
Why moisture determines everything
Freshly felled wood is roughly half water. That water has to evaporate before the wood can burn.
That evaporation costs energy, and that energy comes from your fire. If you burn wood with forty per cent moisture, a considerable part of the combustion heat goes into boiling the water in the wood itself. What is left heats your room — and that is noticeably less than with dry wood.
The second problem is incomplete combustion. A fire that burns too cool does not burn the gases completely. They condense in the chimney as creosote: a tar-like deposit that causes chimney fires. So burning wet wood is not just inefficient but also unsafe.
And the third: smoke. Incomplete combustion is exactly what produces fine particulates and odour nuisance. A large share of complaints about wood stoves in residential areas comes from wood that is too damp, not from burning itself.
A moisture meter costs little and is easy to use: split a log and measure on the fresh split face in the middle — not on the outside, which is always drier. If the reading stays below twenty per cent, you can burn it.
- Target value
- maximum 20 per cent moisture
- Freshly felled
- 40 to 60 per cent
- Drying softwood
- about 1 year
- Drying hardwood
- 1.5 to 2 years
- Split wood dries
- much faster than unsplit logs
- Measuring
- on a fresh split face, in the middle
- Never burn
- pressure-treated, painted or glued wood
To be fair: drying properly takes space and time that not everyone has. Storing a year and a half's supply under a lean-to with air around it is simply not feasible if you have a small garden. Then buying kiln-dried wood is the most honest solution — more expensive per cubic metre, but you get more heat out of it.
How to dry firewood
- Split it, don't leave it wholeUnsplit logs dry slowly because the bark holds in the water. Split wood has open faces and dries many times faster.
- Stacked, off the groundOn pallets or beams, never directly on the soil. The wood draws up moisture from below.
- Air in betweenStack loosely, with space between the logs and between the rows. A tight stack dries on the outside and stays wet inside.
- A roof, not a tarpaulinA lean-to or corrugated sheet above the stack keeps the rain off. A tarpaulin over the whole stack traps moisture and has the opposite effect.
- Sun and windWind does more than sun. Put the stack where the wind can blow through it, not tight against a wall.
- PatienceSoftwood about a year, hardwood one and a half to two. Oak takes the longest — and is worth it.
Which species for the stove
| Species | Burning properties | Drying time |
|---|---|---|
| Beech | high heat output, steady flame — the classic | ± 2 years |
| Oak | burns long and hot; needs to be properly dry | 2 years or more |
| Ash | burns well and dries relatively quickly | 1 – 1.5 years |
| Birch | catches easily, attractive flame, burns up quickly | ± 1 year |
| Hornbeam | very high heat output | ± 2 years |
| Pine and spruce | lights easily, lots of sparks from resin | ± 1 year |
| Poplar and willow | little heat, burns up quickly | ± 1 year |
Pressure-treated wood, painted or varnished wood, chipboard, plywood, MDF and pallet wood with unknown treatment. When burned, these release substances you do not want in your home and that damage your chimney. They belong at the recycling centre.
Better burning with dry wood
Light it from the top
Large logs at the bottom, smaller ones on top, kindling at the very top. The fire then burns downwards and burns the gases straight away — much less smoke than lighting it at the bottom.
Let the air in
A stove that is choked down gives a smouldering fire with lots of smoke and creosote. Better a smaller fire that burns well than a large fire you smother.
Small logs
A few smaller logs burn cleaner than one large log, because more surface area is available.
Warm up the chimney
A cold chimney draws poorly. A short, hot start with thin wood gets the draught going.
Bring wood inside a day ahead
Logs you bring in a day before use are drier on the outside and catch more easily.
Have the chimney swept
Every year, even if you burn dry wood. In many municipalities it is also compulsory and a condition of your insurance.
Frequently asked questions about drying firewood
How dry should firewood be?
Maximum twenty per cent moisture. Above that, a large part of the heat goes into evaporating water and you get smoke and creosote instead of warmth.
How long does wood need to dry?
Softwood about a year, hardwood one and a half to two years. Oak takes the longest. Split wood dries much faster than unsplit logs.
How do I measure the moisture content?
With a moisture meter, on a fresh split face in the middle of a log. The outside is always drier and gives too favourable a picture.
Can I put a tarpaulin over my woodpile?
Only on top. A tarpaulin that covers the whole stack traps moisture and prevents drying — it has the opposite effect.
Which wood gives the most heat?
Beech, oak and hornbeam. Softwood burns faster and sparks because of the resin; birch burns beautifully but burns up quickly.
What should I definitely not burn?
Pressure-treated, painted or varnished wood, and board materials such as chipboard, plywood and MDF. These release harmful substances when burned.
More in The Wood Guide
Each wood species has its own page, with properties and uses.
Have a question about your project? Just ask — we're happy to help.
Photos via Wikimedia Commons: Firewood under a lean-to with open sides, so it dries in the wind — 4028mdk09, CC BY-SA 3.0 · Split firewood neatly stacked, end grain facing out — Feci1024, CC BY 3.0