Kiln Drying vs Air Drying Firewood: Which Process Is More Sustainable?

Why the Firewood Drying Method Matters

Kiln-dried firewood is widely recognised for its higher heat output, lower emissions, and reduced maintenance costs for stoves and chimneys. However, a common misconception remains: that kiln drying is less environmentally friendly than air drying.

In reality, when analysed from a full production and energy-efficiency perspective, an industrial kiln drying process can be more sustainable than traditional air drying. Below, we explain why — using real production data from VLI Timber, one of Europe’s leading kiln-dried firewood manufacturers.
Learn more about the company and its production standards on the About VLI Timber page.

Air-Dried vs Kiln-Dried Firewood: Energy Output Comparison

From 100 m³ of raw birch wood, two different drying methods lead to significantly different results.

• Air-dried firewood production results in an energy output equivalent to 201,920 kWh

• VLI Timber’s kiln drying process produces 226,970 kWh, which equals 12% more renewable energy compared to air drying

This difference is not theoretical — it is the result of material efficiency and controlled industrial processing.

The diagram below compares air-dried and kiln-dried firewood production based on identical input volumes, illustrating differences in material losses, moisture content, and total renewable energy output.

Material Losses in the Air-Drying Process

In a traditional air-drying process:

• From 100 m³ of birch wood, approximately 5 m³ is lost over 12 months due to natural rotting

• An additional 7 m³ of wood waste is generated during splitting

• This leaves only 88 m³ of air-dried logs

VLI Timber’s Kiln Drying Process: Controlled and Efficient

In contrast, VLI Timber’s kiln drying process is based on closed-loop, industrial efficiency:

• 7 m³ of sawdust and wood waste is reused to heat biomass boilers

• Electricity equivalent to 0.17 m² of wood is used to operate the kilns

• Logs are dried within 45–60 hours, not months

In total, only 7.17 m³ of wood is consumed in the drying process — and it is used efficiently, not wasted. This makes VLI Timber a zero-waste firewood manufacturer.

After splitting and kiln drying 100 m³ of wood, the result is:

• 95 m³ of logs with 15% moisture content, ready for immediate use

• Higher combustion efficiency and heat output

• Total renewable energy production of 226,970 kWh, up to 12% more than air-dried firewood

An overview of VLI Timber’s industrial kiln-dried firewood production can be found here.

What About CO₂ Emissions?

A frequent question is whether kiln drying produces more CO₂ than air drying.

The answer may be surprising:
VLI Timber’s kiln drying process and air drying generate the same total amount of CO₂.

Additionally, leaving the same 100 m³ of wood to rot in the forest releases the same amount of CO₂ as kiln drying the wood and burning it in a stove. This is because wood emits the same amount of CO₂ when decomposing as it does when burned.

From a carbon perspective, controlled kiln drying does not increase emissions, while delivering higher usable energy output.

Continuous Improvement in Firewood Production

To achieve the environmental and efficiency benefits outlined above, VLI Timber fully modernised its wood drying process in 2020. Continuous improvement remains a core part of the company’s operational culture, with ongoing investments in energy efficiency, process optimisation, and sustainable manufacturing.

Why Industrial Kiln-Dried Firewood Is the Smarter Choice

• Higher renewable energy yield from the same raw material

• Lower material losses and zero-waste production

• Stable moisture content and predictable combustion performance

• No additional CO₂ impact compared to air drying

For large-scale supply, industrial partnerships, or technical specifications, contact the VLI Timber team directly.