Guide · Moisture & Kiln-Drying
Firewood moisture content and kiln-drying — the wholesale buyer's guide.
Moisture content is the single most important firewood spec. It determines legality in the UK, saleability in the Nordics, heat output on the customer's stove and the merchant's return rate. This is how it's measured, why sub-20% matters, and how we hit it every load.
Under 20% is the standard
UK Ready to Burn, Nordic Swan and Irish Solid Fuel specs all target sub-20% moisture. Kiln-drying is the only reliable way to guarantee it.
Resistance-meter tested
Every batch is verified on a freshly split face with a calibrated meter — the industry-standard method used by both mills and buyers.
Certificate per container
Every Timberlink container ships with a batch-linked moisture certificate and PEFC chain-of-custody documentation.
Why moisture matters more than species
The difference between good and bad firewood is moisture, not species. A crate of birch at 15% moisture will outperform a crate of oak at 30% on the customer's stove — faster to light, cleaner burn, higher effective heat output.
This is why every European market has converged on moisture as the primary regulated spec. UK Ready to Burn, Nordic Swan, Irish Solid Fuel Regulations and most merchant procurement contracts all target sub-20% moisture as the working standard.
How moisture is measured
The industry standard is an electrical resistance meter with two probes pushed into a freshly split face at the mid-length of the log. Surface readings are meaningless — moisture lives inside the wood.
A batch is tested at multiple points across multiple crates. If the average is under 20% with no outliers above the threshold, the batch is released. Oven-drying to constant weight is the laboratory reference method but is impractical for daily trade use.
How kiln-drying actually works
Split logs are loaded into insulated chambers holding 40–80 m³ per load. Chamber temperature ramps to 65–80°C with engineered airflow so every crate sees warm dry air on all sides. Heat comes from biomass boilers burning the mill's own residues — no fossil fuel input.
A birch cycle runs 5–8 days. Oak, being denser, needs 10–14 days. At the end of the cycle a technician tests moisture at multiple points; anything above 18% average goes back in for another day or two.
Why air-seasoning stopped being enough
Air-seasoning was the default across Europe for centuries. It still works — in a dry climate, over 18–24 months, air-seasoned hardwood can reach 20–25% moisture.
The problem is consistency. One pallet air-seasons beautifully, the next steams. In northern European climates the practical floor is 25–30% moisture, and that's not good enough for Ready to Burn compliance or modern stove performance. Kiln-drying is the only method that guarantees sub-20% on every stick.
The energy penalty of wet wood
Burning firewood at 30% moisture wastes roughly 20–25% of the wood's energy evaporating water instead of heating the room. Sap and steam also condense in the flue, forming creosote — the primary cause of chimney fires.
Sub-20% kiln-dried wood delivers the rated kWh/kg (oak ≈4.2, ash ≈3.9, birch ≈3.3). Wet wood doesn't. This is the numeric case for kiln-dried at the customer's end of the transaction.
Storing kiln-dried firewood without losing spec
Kiln-dried hardwood is stable at sub-20% for 6+ months in dry, ventilated storage. Store crates off the ground on pallets or bearers, under cover (a roof, not a wrap), with airflow around all four sides.
Avoid sealing kiln-dried wood in plastic without vents — trapped moisture re-enters the surface layers. Rotate stock first-in first-out; the oldest crate on your yard should be the next one sold.
Certification schemes to know
Ready to Burn (UK): Woodsure-administered, mandatory for pack sizes under 2m³, certifies sub-20% moisture. Nordic Swan (SE/NO/DK/FI): broader environmental label including moisture, particulates and sourcing. Irish Solid Fuel Regulations: aligned with UK spec, under 20% moisture the practical merchant standard.
PEFC and FSC chain-of-custody are separate certifications covering sustainable sourcing rather than moisture — but most tenders now require both a moisture certificate and a chain-of-custody number.
Frequently asked
What moisture content should firewood be below?+
Under 20% moisture is the working standard across Europe. UK Ready to Burn requires it for pack sizes under 2m³, and Nordic Swan and most merchant procurement specs match it. Our kiln-dried hardwood typically ships at 12–18%.
How is firewood moisture measured?+
With a calibrated electrical resistance meter on a freshly split face — not the outer surface. Two probes are pushed into the wood mid-length, and the reading is taken at multiple points across a batch. Oven-drying to constant weight is the laboratory reference method but is rarely used in the trade.
How long does kiln-drying firewood take?+
Birch reaches under 20% moisture in a 5–8 day chamber cycle at 65–80°C. Denser hardwoods like oak need 10–14 days. Softwoods dry faster but are rarely worth kiln-drying for merchant sale.
Why not just air-dry firewood?+
Air-seasoning is inconsistent, weather-dependent and typically stops around 25–30% moisture in northern European climates. Kiln-drying pushes every stick below 20% in a controlled cycle — the only way to guarantee Ready to Burn compliance on every crate.
Does kiln-dried firewood re-absorb moisture?+
Only slowly, and only if stored badly. Kept dry and ventilated, kiln-dried hardwood stays under 20% for 6+ months. Store it off the ground, under cover, with airflow around the crates.
What's the energy penalty for burning wet wood?+
At 30% moisture, roughly 20–25% of the wood's energy is wasted evaporating water instead of heating the room. Kiln-dried sub-20% wood delivers the rated heat output; wetter wood does not.
What certification proves the moisture claim?+
In the UK, Woodsure's Ready to Burn scheme. In the Nordics, Nordic Swan. Every Timberlink container also ships with a per-batch moisture certificate signed against resistance-meter readings at the mill.
How does kiln-drying affect heat output?+
It preserves it. The published kWh/kg figures for oak, ash, birch and alder all assume sub-20% moisture. Wetter wood underperforms those numbers; kiln-dried wood hits them.
Company & credentials
A registered Latvian exporter merchants can verify
Timberlink is a fully registered timber exporter operating out of the Riga region for a decade. Every credential below is publicly verifiable — no white-label middlemen, no drop-shipping.
- Registered company
- SIA Timberlink
- Registration No.
- 40203747426
- VAT No.
- LV40203747426
- Legal address
- Airu iela 1A, Baltezers, Garkalnes pag., Ropažu nov., LV-2164, Latvia
- Years in operation
- 10 years
- Certification
- PEFC/12-31-065
Chain of Custody
Every load is traceable to sustainably managed Baltic forests under the PEFC scheme.
Legal timber
Full EUTR due-diligence documentation supplied with every export shipment.
Export paperwork
Customs, phytosanitary and origin documents prepared per destination country.
Shipping & export logistics
Baltic ports
Regular full-load departures via Riga and Liepāja for UK, Ireland, Nordics and North Sea markets.
Road freight
Direct trailer deliveries into Germany, Denmark, Netherlands, France and Scandinavia.
Full-container loads
20ft and 40ft container loading to spec, with lashing photos and load lists per shipment.
COMPETITIVE RATES FOR MERCHANTS & BUSINESS CLIENTS
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