What are wood pellets?
Wood pellets are small cylindrical rods pressed under high pressure from dry wood residue — sawdust and planer shavings from the timber industry. No glue is involved: the lignin in the wood softens under the frictional heat and binds the material together.
The result is a fuel with low moisture content and a uniform shape that can be dosed automatically by an auger. That is why a pellet stove or boiler can run on a thermostat, unlike an ordinary log stove.
Quality requirements (ENplus A1)
The most widely used certification scheme in Europe is ENplus, with A1 as the top class for domestic use. ENplus A1 requires, among other things:
- Diameter: 6 or 8 mm
- Moisture content: maximum 10 %
- Ash content: maximum 0.7 %
- Calorific value: roughly 4.6 to 5.3 kWh per kg
A low ash content means emptying the ash pan less often and less deposit in the stove and flue. DINplus is a comparable scheme with partly identical requirements. Uncertified pellets may contain more bark, sand or moisture, which causes clinker, more maintenance and occasional auger jams.
Practical points
- Store dry. Pellets take up moisture and then crumble to sawdust. Keep bags indoors on a pallet, not on a damp concrete floor in a shed.
- Handle gently. Dropping and decanting breaks pellets, and the resulting fines cause most of the faults. A good supplier blows bulk pellets in at low velocity.
- Rule of thumb. At roughly 4.6 to 5.3 kWh per kg, a 15 kg bag yields around 70 to 80 kWh of heat, less the appliance’s losses.
- Flue. A pellet appliance needs its own sealed flue and normally a mains connection for the auger and fan.
Check the rules for solid fuel appliances where you live: emission limits apply to new appliances, installations usually need commissioning and inspection, and local authorities may issue air quality warnings. Never burn painted, glued or treated wood — which also means avoiding pellets of unknown origin.
Related terms
- Biomass
- Pellet stove
- Flue
- Moisture content of timber
- Calorific value
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.