Wood pellet is a solid fuel that is produced by crushing and densifying waste timber like sawdust, forestry residues, forestry wastes. The length is 1-4cm and the diameter is generally 6, 8, 10, or 12mm. It is possible to produce 25mm wood pellet at maximum. In Sweden, 6mm wood pellet is encouraged to use in house as it can realize the best condition of combustion.