The Complete Guide to Firewood Moisture Content: Why It Matters More Than Wood Species
Firewood Moisture Content: The Complete Expert Guide
When people buy firewood, they often focus on one question:
"Should I buy hardwood or softwood?"
While that's an important consideration, it's actually not the most important one.
In our experience, the biggest factor affecting how well firewood performs is moisture content.
At Surefire Wood, we've spent decades producing premium kiln dried firewood for homes, businesses and commercial customers throughout Ireland and the United Kingdom. As Ireland's leading producer and one of Europe's largest producers of kiln dried firewood, we've processed thousands of tonnes of timber every year.
One lesson has remained constant:
A dry log will almost always outperform a wet log, regardless of species.
Whether you're burning Ash, Oak, Beech, Spruce or Larch, moisture content has a greater impact on heat output, efficiency and stove performance than almost any other factor.
This guide explains why.
Quick Answer
If you're looking for the short answer:
Firewood should contain less than 20% moisture.
In Ireland, look for WFQA Ready to Burn certification.
In the UK, look for Woodsure Ready to Burn certification.
These certification schemes independently verify that the firewood is dry enough to burn efficiently.
What Is Moisture Content?
Every tree contains water.
Even after it's cut, that moisture remains trapped inside the timber.
Freshly felled trees can contain 40–60% moisture, depending on:
- Tree species
- Age
- Growing conditions
- Time of year
- Part of the tree
Before firewood burns efficiently, that excess water must be removed.
Why Moisture Matters
Imagine trying to boil a kettle before you can heat your house.
That's essentially what happens when you burn wet firewood.
Before the wood can release its stored energy, your fire first has to evaporate the water inside the logs.
That means:
- Less useful heat
- More smoke
- Poor combustion
- Blackened stove glass
- Increased soot
- More creosote
- Lower efficiency
Every litre of water inside the log represents energy that never heats your home.
What Happens When Firewood Is Too Wet?
Firewood above 20% moisture commonly causes:
Poor Heat Output
Your stove spends energy drying the logs rather than heating the room.
More Smoke
Wet wood creates incomplete combustion.
This increases visible smoke and airborne particles.
Dirty Stove Glass
One of the biggest complaints from stove owners is blackened glass.
Very often the cause isn't the stove.
It's damp fuel.
Chimney Deposits
Wet firewood encourages the build-up of soot and creosote.
Over time this increases maintenance requirements and, in severe cases, can increase the risk of chimney fires.
Why Less Than 20%?
Years of research and industry experience have shown that below 20% moisture provides the best balance.
At this level firewood:
- Lights easily
- Burns cleanly
- Produces excellent heat
- Creates fewer emissions
- Keeps your stove cleaner
This is why recognised certification schemes use this threshold.
WFQA & Woodsure Ready to Burn
Whether you're buying firewood in Ireland or the UK, independent certification gives you confidence that your fuel meets recognised standards.
Ireland
Look for:
WFQA Ready to Burn
United Kingdom
Look for:
Woodsure Ready to Burn
These certification schemes verify that the firewood contains less than 20% moisture, helping homeowners and businesses choose fuel that's ready to burn immediately.
How Is Moisture Measured?
Professional firewood producers don't simply guess.
Moisture is measured using calibrated moisture meters.
The meter measures the electrical resistance within the timber.
Because water conducts electricity differently from dry wood, it provides an accurate indication of moisture content.
For best results:
- Split the log.
- Test the freshly exposed centre.
- Measure several logs.
Testing only the outside of a log can give misleading readings because the surface dries faster than the middle.
How Kiln Drying Works
Kiln drying isn't simply about heating wood.
Producing premium firewood requires careful control of:
- Temperature
- Airflow
- Drying time
- Timber species
- Log size
Different species dry at different rates.
Dense hardwoods such as Oak require different drying profiles from Spruce or Larch.
Producing consistently dry firewood requires both experience and careful quality control.
Moisture Content by Firewood Stage
| Firewood Condition | Typical Moisture Content | Suitable for Burning? |
|---|---|---|
| Freshly felled | 40–60% | ❌ No |
| Part-seasoned | 25–35% | ❌ No |
| Well-seasoned | 20–25% | ⚠ Sometimes |
| Kiln dried / Ready to Burn | Below 20% | ✅ Yes |
Moisture vs Heat Output
Imagine two identical Ash logs.
One contains 18% moisture.
The other contains 35%.
Although they're the same species, the drier log will generally:
- Light faster.
- Produce more usable heat.
- Burn more efficiently.
- Generate less smoke.
- Leave fewer deposits in the chimney.
That's why moisture content always comes before species.
Common Moisture Myths
"Hardwood doesn't need drying."
False.
Fresh Oak can contain huge amounts of moisture.
"Softwood is always wetter."
False.
Properly kiln dried Spruce often contains less moisture than naturally seasoned hardwood.
"If it feels dry, it's ready."
Not necessarily.
The centre of the log may still contain excessive moisture.
"Seasoned always means ready to burn."
No.
Seasoning time, weather and storage all influence the final moisture content.
Expert Insight from Surefire Wood
After drying and supplying thousands of tonnes of firewood every year, we've learned that moisture consistency is one of the biggest indicators of quality.
Two loads of Ash may look almost identical, but if one has been dried correctly and the other hasn't, they'll perform very differently.
Customers often assume species alone determines quality.
In reality, moisture content is usually the deciding factor.
That's why every stage of our production process focuses on producing consistently dry firewood that delivers reliable performance from the first log to the last.
Frequently Asked Questions
What moisture content should firewood be?
Below 20%.
Can I burn 25% moisture logs?
You can, but they won't perform as efficiently and will generally produce more smoke and less heat.
Is lower than 20% always better?
Not necessarily. Firewood dried to the recognised Ready to Burn standard provides an excellent balance between combustion, heat output and usability.
How do I test my firewood?
Split a log and measure the freshly exposed centre using a moisture meter.
Why is my stove glass black?
One common cause is burning fuel with excessive moisture, although poor airflow and stove operation can also contribute.
Does Oak need to be drier than Spruce?
No. Regardless of species, the same moisture principles apply.
Final Thoughts
When choosing firewood, don't make moisture content an afterthought.
Make it your first consideration.
Whether you prefer Ash, Oak, Beech, Spruce or Larch, properly dried logs will provide better heat, cleaner combustion and improved stove performance.
For peace of mind, choose WFQA Ready to Burn certified firewood in Ireland or Woodsure Ready to Burn certified firewood in the United Kingdom. Combined with correct storage and good stove operation, it will help you enjoy more efficient fires and greater value from every load of logs.
Inside Our Moisture Testing Process
Producing premium firewood isn't simply about drying timber and hoping for the best. At Surefire Wood, moisture content is monitored as part of our quality assurance process to help ensure consistent performance across every batch.
Different timber species behave differently during drying. Dense hardwoods such as Oak, Ash and Beech release moisture at a different rate to Spruce and Larch, so drying schedules are carefully managed to achieve consistent results.
Before firewood reaches our customers, representative samples are checked to verify that the timber meets recognised Ready to Burn standards. This commitment to quality is one of the reasons customers across Ireland and the UK rely on Surefire Wood for dependable, high-performance kiln dried firewood.