Wood pellets for use with stoves for room heating and for those which give full central heating capability are the subject of my first blog.

1. Wood pellets are manufactured by hot-extruding compressed sawdust which is produced during the working of natural dried wood. The compactness of the material comes from the lignin which is contained in the wood itself, and allows the production of pellets without the use of glues or binders.

2. The market offers different types of pellet with characteristics which vary depending on what mixture of woods is used. The diameter varies between 6 mm and 8 mm, with a standard length in the range 5 mm to 30 mm.

3. Good quality pellets have a density which varies between 600 kg/m3 and 750 kg/m3, with a moisture content which varies from 5% to 8% by weight.

4. Wood pellet is an ecological fuel. It exploits timber residues to the maximum and achieves cleaner combustion than is possible with fossil fuels.

5. Pellets also have technical advantages. While good-quality timber has a calorific power of 4.4 kW/kg (with 15% moisture, ie after about 18 months' seasoning), the equivalent figure for pellets is 4.9 kW/kg.

6. To ensure they burn well, the pellets must be stored in an area that is free of humidity and protected from dirt.

7. The pellets are usually supplied in 10 to 15 kg sacks, so storing them is convenient.

8. The poorer the quality of the fuel, the less well it will burn and the more frequently you will need to clean the internal parts, such as the grate and the combustion chamber.

9. The main certifications of quality for pellets in the European market are DINplus and Ö-Norm M7135; these ensure the following qualities:
•    Calorific power: 4.9 kW/kg
•    Water content: max 10% of weight
•    Percentage of ashes: max 0.5% of weight
•    Diameter: 5 to 8 mm
•    Length: max 30mm
•    Contents: 100% untreated wood, with no added bonding substances (bark percentage 5% max). We strongly recommend using certified fuel in pellet stoves to European standards (DINplus and Ö-Norm M7135).

10. If you use fuel of inferior quality, or not conforming to the specification given above, it compromises the running of your stove and can lead to the termination of the guarantee and of the manufacturer's responsibility for the product. 

11. Pellet stoves run exclusively on pellets with a diameter of 6-8 mm with lengths that range from 5 mm to 30 mm.

12. Recently the supply of pellet from distributors has become very good. The number of manufacturers & distributors coming on line is increasing all the time. This will hopefully  mean the price of pellets will get cheaper more competitive and they will be more readily available.

Photo by Baston/iStock

About the author: Mike Mackmurdie is the director of A Mackmurdie Ltd, installers of biomass and solar water heating.

If you have a question about anything in the above blog, please ask it in the comments section below.