Across Europe and North America, more households are turning back to wood stoves and fireplaces to cut energy bills. Dry firewood is the key to clean, efficient heat, yet many people only realise their logs are still damp once the fire sulks and the glass blackens. A simple bottle of washing-up liquid could spare you the disappointment.
Why dry firewood matters more than you think
Burning wet wood is not just a nuisance. It has real consequences for your wallet, your stove and the air you breathe.
Good firewood should have a moisture content below roughly 20%. Above that, much of the heat is wasted evaporating water instead of warming your home.
When logs are still green or poorly seasoned, three things happen:
- The fire is harder to light and slow to catch.
- The stove glass and flue get coated with sticky deposits.
- Smoke and fine particles increase, inside and outside the house.
Over time, these deposits can raise the risk of chimney fires and force you into more frequent (and costly) sweeping. In some regions, local air-quality rules already restrict burning damp wood for this reason. So checking your logs before the heating season is not just a nerdy detail; it affects comfort, safety and running costs.
First clues: what dry wood looks, feels and sounds like
You can learn a lot just by looking at and handling your logs. Seasoned wood shows a few recurring signs.
Cracks, bark and colour
As water leaves the log, it shrinks and splits. Dry pieces usually have:
- Small to large cracks at the cut ends.
- Bark that peels off with little effort or has already fallen.
- A slightly greyer or duller tone than freshly cut wood.
If you spot mould, mushrooms or soft, spongy spots, the wood has been stored too damp. That does not mean it is still wet inside, but it does point to poor storage and possible loss of heating value.
The smell and weight test
Freshly cut wood often smells strongly of sap or resin. Once properly seasoned, that scent fades.
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A dry log usually feels surprisingly light for its size and carries only a faint, woody smell instead of sticky sap.
Grab two similar pieces from the pile. If one is noticeably heavier and still smells “green”, it likely contains more moisture than the lighter, dull‑smelling one.
The “clack” of two logs
Old-fashioned but still useful, the sound test is quick:
- Bang two logs together.
- A clear, ringing “clack” suggests drier wood.
- A dull, thudding sound often means the core is still damp.
It is not laboratory science, and dense hardwoods can sound less bright by nature, but it gives a decent first impression when you are sorting a stack.
The washing-up liquid trick: how bubbles reveal moisture
Among the home methods, one stands out for its simplicity and oddly satisfying result: the bubble test using ordinary washing-up liquid.
Step-by-step bubble test
You only need a cut log, a bit of washing-up liquid and your lungs.
If the wood is dry enough, air will travel through the tiny channels in the grain and form visible bubbles in the soap at the other end.
When no bubbles appear at all, or the soap just sits there, the internal fibres may still be clogged with water. The log can look dry outside but remain damp at the core, especially if it was split late or stored in thick rounds.
When this trick works best
The bubble test is not perfect, yet it does highlight how open and dry the wood’s structure has become. It tends to work better when:
- The log is not too long (shorter pieces allow air to pass more easily).
- The grain is fairly straight rather than twisted or knotty.
- The ends are cleanly cut, not splintered.
Think of it as a practical backup to your eyes and ears. If a piece looks and sounds seasoned and also raises bubbles with this method, chances are high it is ready for the stove.
Tech tools: using a moisture meter for hard numbers
For people who buy several loads of wood or rely heavily on a stove, a small moisture meter can remove guesswork.
| Method | Main strength | Main drawback |
| Visual check | Instant, free | Can mislead on some species |
| Sound test | Quick, no tools | Subjective, depends on ear |
| Washing-up liquid bubbles | Fun, highlights internal dryness | Tricky on long or knotty logs |
| Moisture meter | Numeric, repeatable | Small upfront cost |
Most inexpensive pin-type meters work in a similar way:
- Push the metal probes into the freshly split face of a log.
- Take readings from several pieces in the batch.
- Aim for a value below about 20% before burning.
Taking measurements on a newly split surface is crucial. The outer shell can be quite dry while the middle still reads far higher. By sampling a handful of logs from different parts of the stack, you get a realistic picture of the whole load.
Storing wood so it actually dries
No clever test will fix badly stored logs. Seasoning is mostly about time and air movement.
The best “dryer” for firewood is free: outdoor air and wind, with a roof overhead and the logs lifted off the ground.
For effective seasoning:
- Stack wood outside under a simple roof or lean-to, open on at least two sides.
- Keep the first row raised on pallets, blocks or rails.
- Leave small gaps between pieces so air can weave through the pile.
- Face the cut ends towards the prevailing wind if possible.
Closed garages, cellars and garden sheds often trap moisture rather than remove it. Wood stored there can look aged but may still carry extra water weight, making any later test less encouraging.
How long should firewood season?
Timing depends on species, climate and how the logs are cut.
- Softwoods (pine, spruce, fir): often usable after 6–12 months if split early and stacked well.
- Medium hardwoods (birch, poplar): commonly need around 12–18 months.
- Dense hardwoods (oak, beech, hornbeam): can require 18–24 months, sometimes more in damp climates.
Splitting logs soon after cutting speeds the process. Chunky rounds left untouched can still be wet inside after two years. This is where a mix of tests – look, sound, washing-up bubbles and, if you have one, a meter – helps you avoid guesswork.
What “moisture content” actually means
When people talk about 20% moisture content, they are describing the proportion of water compared with the dry mass of the wood.
Freshly felled logs can easily contain 50% moisture or more. As the water evaporates, the percentage falls, making the wood lighter and more energy dense per kilo. Below about 20%, combustion becomes far cleaner. Flue gases cool less, soot builds up more slowly, and you get closer to the efficiency figures quoted for modern stoves.
A winter scenario: testing a random load of logs
Imagine a family who ordered two cubic metres of mixed hardwood in late spring. The seller promised “ready to burn”, but the pile was delivered tightly stacked and has sat under a tarpaulin ever since.
On a chilly October afternoon, they decide to check. A quick inspection shows some end cracks but the bark clings stubbornly. The sound test gives a mixed result: a few pieces ring nicely, others thud. Curious, they grab a short log, add a smear of washing-up liquid to one end and blow from the other. For several pieces, bubbles rise instantly. For others, nothing.
They split one of the heavier logs and press a moisture meter into the fresh face. The display reads 28%. Those pieces go back onto a better-ventilated rack for use later in the season. The lighter, bubble‑producing logs cluster around 18–20% and become the first candidates for the fire. By combining simple observations with the washing-up trick, they avoid a smoky, disappointing first burn.
Health and environmental angles to keep in mind
Dry wood does not just mean more comfort. It also lowers emissions of fine particles and unburned hydrocarbons linked to respiratory problems. In neighbourhoods where many homes use stoves, the difference between wet and dry wood adds up to a real air‑quality issue on cold, still evenings.
From a maintenance perspective, running a stove on properly seasoned logs helps keep flues cleaner for longer. That does not replace professional sweeping, but it can reduce the amount of tar-like creosote left in awkward bends and joints, where it is hardest to remove.
Putting a few minutes into testing your logs, with tools as basic as eyesight, hearing and a drop of washing-up liquid, can turn a frustrating, smoky winter into one of reliable, comforting fires that work with your stove rather than against it.