Across Europe and North America, a growing number of households are returning to wood stoves and fireplaces to reduce energy costs. For this to work properly, dry firewood is essential. Unfortunately, many people only realise their logs still hold moisture when the fire struggles to burn and the stove glass turns black. Surprisingly, a simple bottle of washing-up liquid can help prevent that frustration.
Why properly dried firewood makes a real difference
Using damp logs is more than just inconvenient. It directly affects heating efficiency, appliance condition, and air quality. Firewood should ideally contain less than 20% moisture. When levels are higher, a large share of the heat is lost to evaporating water instead of warming your home.
When wood is unseasoned or still green, several problems appear:
- The fire becomes difficult to ignite and slow to establish.
- Sticky residues build up on stove glass and inside the flue.
- Smoke and fine particles increase both indoors and outdoors.
Over time, this buildup can raise the risk of chimney fires and lead to more frequent, costly cleaning. In some areas, burning wet wood is already restricted due to air-quality regulations. Checking your logs before winter directly affects comfort, safety, and running costs.
Early signs: how seasoned wood looks, feels, and sounds
You can often judge firewood quality using simple observation. Well-seasoned logs tend to share clear visual and physical traits.
End cracks, bark condition, and colour changes
As moisture escapes, wood contracts and splits. Dry logs usually show:
- Visible cracks on the cut ends.
- Bark that loosens easily or has already fallen away.
- A duller, greyer tone compared with freshly cut wood.
If you notice mould, fungal growth, or spongy areas, the wood was stored in damp conditions. While this does not always mean the core is wet, it often signals reduced heating value.
Smell and weight as quick indicators
Fresh logs usually release a strong sap or resin scent. Once properly seasoned, this smell largely disappears.
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A dry log typically feels noticeably lighter than expected and carries only a faint woody aroma. If two similar-sized logs are compared, the heavier, stronger-smelling piece usually contains more internal moisture.
The sound test: listening for dryness
This traditional method still offers useful clues:
- Strike two logs together firmly.
- A sharp, ringing clack points to drier wood.
- A dull thud often signals remaining moisture.
Although dense hardwoods naturally sound less bright, this test provides a quick first impression when sorting firewood.
The washing-up liquid bubble method explained
One of the simplest household techniques is the washing-up liquid bubble test, which reveals internal moisture surprisingly well.
How to perform the bubble test
You need only a cut log, washing-up liquid, and your breath:
- Select a log with straight grain and no rot.
- Apply a small amount of washing-up liquid to one cut end.
- Spread it into a thin soapy layer.
- Place your mouth on the opposite cut end.
- Blow firmly for several seconds.
If the wood is dry, air travels through the grain and creates visible bubbles in the soap. When nothing appears, moisture may still be blocking the internal fibres, even if the surface looks dry.
Situations where this test works best
The bubble method is most effective when:
- The log is short enough for air to pass through.
- The grain runs fairly straight.
- The ends are cleanly sawn rather than splintered.
Used alongside visual checks and sound testing, bubbling strongly suggests the wood is ready for burning.
Moisture meters for precise readings
For those who rely heavily on wood heating, a moisture meter removes uncertainty. Each method has strengths and limits:
- Visual checks are instant and free but can mislead.
- Sound testing is fast but subjective.
- Bubble testing highlights internal dryness but struggles with knotty logs.
- Moisture meters provide numeric, repeatable results at a small upfront cost.
To use a meter correctly:
- Split a log and insert probes into the fresh inner face.
- Test several logs from different stack areas.
- Aim for readings below 20% before burning.
The outer surface can dry faster than the core, so internal measurements give a more accurate picture.
Storing firewood so it truly dries
No test compensates for poor storage. Effective seasoning depends on time, airflow, and protection from ground moisture.
For best results:
-
- Store logs outdoors under a roof, open on at least two sides.
- Raise the stack on pallets or rails.
- Leave gaps between pieces for airflow.
- Position cut ends toward the prevailing wind.
Garages and sheds often trap moisture, making wood appear aged while still retaining excess internal water.
How long different woods need to season
Drying time varies by species and conditions:
- Softwoods often dry within 6–12 months.
- Medium hardwoods usually need 12–18 months.
- Dense hardwoods may require 18–24 months or longer.
Splitting logs early accelerates drying, while thick, unsplit rounds can remain damp for years.
Understanding moisture content in simple terms
Moisture content describes how much water remains compared with the wood’s dry mass. Freshly cut logs may exceed 50% moisture. As water evaporates, the wood becomes lighter and more energy-dense. Below 20%, combustion is cleaner and more efficient, reducing soot and improving stove performance.
A real-world winter check
Consider a household that buys mixed hardwood labelled “ready to burn.” Delivered tightly stacked and covered, the logs sit untouched until autumn. When tested, some show cracks while bark still clings. Sound tests vary. Using washing-up liquid, some logs bubble immediately, others not at all.
A heavier piece splits open and reads 28% on a moisture meter, so it is stored longer. Lighter logs showing bubbles measure around 18–20% and are used first. This combination of checks prevents a smoky, inefficient start to winter heating.
Health and environmental considerations
Burning dry wood reduces fine particle emissions linked to respiratory issues and improves neighbourhood air quality on cold, still nights. Properly seasoned fuel also helps keep flues cleaner, limiting creosote buildup in hard-to-reach areas.
Spending a few minutes testing firewood using sight, sound, and a drop of washing-up liquid can transform winter heating into a reliable, clean, and efficient experience.
