The real cost of wet firewood: Four reasons you should never burn unseasoned logs

Why You Should Never Burn Wet Wood

Freshly cut wood (also called unseasoned firewood) often has a moisture content above 50%, which makes it difficult to light, inefficient to burn, damaging to the environment, and bad for your stove and chimney. Such high moisture levels mean much of the energy is used to evaporate water rather than generate heat.

For better efficiency, we recommend kiln-dried firewood with a moisture level under 20% that meets UK 'Ready to Burn' standards for safe indoor burning. Read on to find out exactly why you should never burn wet wood.

What Is Wet Wood? (Quick Summary)

Firewood which has a moisture content above 20% is described as wet wood. It is:

• Difficult to light and maintain
• Less efficient to burn, producing a lower heat output
• More likely to emit smoke and harmful emissions
• More likely to produce creosote build-up in chimneys

How To Tell If Your Wood Is Too Wet

Wet firewood describes any logs that have a high moisture content, more specifically, higher than 20%. Wet or unseasoned wood doesn't necessarily feel damp to the touch, as it refers to the moisture content within the wood rather than surface moisture. It's difficult to tell how much moisture is in a log just by looking at it.

When timber is first harvested, moisture levels are typically above 50%, meaning more than half the weight of the wood is actually water rather than wood fibre. If the weight of a log is noticeably heavier than a dry log of the same species, it's probably too wet to burn. Other signs include tightly clinging bark, a green-tinged interior, and a dull 'thud' sound when tapped, rather than a hollow 'clack'.

Under the Ready to Burn scheme, firewood must be reduced to below 20% moisture content before it can be legally sold, ensuring cleaner, more efficient burning. Any firewood bearing the 'Ready to Burn' certificate is guaranteed to have a moisture level below 20%.

Why Should You Avoid Burning Wet Wood?

You should avoid burning wet wood because it's inefficient and poor value for money. Here are the four main reasons to avoid burning wet wood:

1. Inefficient to burn: poor heat output
2. Difficult to light
3. Harmful to the environment: increased smoke and emissions
4. Damage to your stove and chimney

Why Is Wet Wood So Inefficient To Burn?

Wet wood is inefficient and has a poor output because excess moisture prevents the fire from reaching its optimal temperature.

Firewood with a high moisture content takes longer to light and, in some cases, may struggle to ignite at all. The kiln-drying process removes moisture not just from the surface, but from the core of the log. This matters because when firewood burns, it releases volatile gases that actually ignite and produce heat.

If wood contains too much moisture, the energy is used to burn off water rather than generate heat. As a result, the fire takes much longer to reach an effective temperature. In addition to reduced heat output, burning wet wood produces high levels of smoke, which can quickly become unpleasant, especially indoors.

Why Is Wet Wood Harmful To The Environment?

Wet wood is harmful to the environment because it produces more smoke and harmful emissions.

Wood with a moisture content above 20% releases higher levels of pollutants when burned. This contributes to air pollution and reduces overall burning efficiency. Kiln-dried logs are a better alternative, as the drying process removes excess moisture and sap, resulting in a cleaner and more environmentally responsible burn.

Does Burning Wet Wood Affect Air Quality And Health?

Burning wet wood negatively affects air quality and can pose risks to human health due to increased PM2.5 emissions.

Pollutants emitted from wet wood include fine particulate matter (PM2.5), which has serious health implications at high exposure levels. However, emissions are not just influenced by fuel — they are also heavily dependent on the type of appliance used.

Independent research conducted for the Stove Industry Alliance by Mitchell and Cottam highlights how emissions vary significantly between appliances:

• Ecodesign stoves: lower emissions, more efficient combustion
• Older stoves: moderate emissions, less efficient
• Open fires: highest emissions and least efficient

This reinforces the importance of using both dry fuel and modern appliances to minimise environmental and health impacts.

Can Wet Wood Damage Your Stove Or Chimney?

Wet wood can damage your stove and chimney by creating residue that builds up over time.

When burned, wet wood produces tar and creosote, which can:

• Blacken stove glass
• Increase cleaning and maintenance requirements
• Restrict airflow in flues

This residue also accumulates inside the chimney, where it can cause corrosive damage and significantly increase the risk of a chimney fire. Burning properly dried firewood (below 20% moisture) helps reduce these risks, keeping both your appliance and chimney in better condition.

What Type Of Wood Should I Be Burning?

You should be burning clean, kiln-dried wood with a moisture content below 20%, as this ensures a hotter, cleaner, and more efficient fire. As we've outlined above, burning wet wood can impact everything from heat output to air quality and stove performance. So, choosing the right fuel is essential if you want a fire that performs well and burns responsibly.

Kiln-dried logs are the best option. They are carefully dried to remove excess moisture, allowing them to light easily, burn consistently, and produce far less smoke. When you choose a 'Ready to Burn' approved supplier like Certainly Wood, you can be confident that the wood meets recognised standards and is suitable for immediate use. Which species of wood to choose is a different matter again — read our guide to different firewood species to decide which is best for your purposes.

The difference between wet and dry wood is easy to see in practice. When comparing wet logs to kiln-dried logs, wet wood often struggles to light and produces excessive smoke, while kiln-dried logs ignite quickly and burn with a strong, steady flame.

If you'd like to understand how fuel choice impacts compliance, read our guide to smoke control zones to ensure you're burning legally, efficiently, and with the right type of firewood.