Why not directly burn logs, wood chips or other biomass materials? One reason is the moisture content. Even the moisture content of air-dried wood tends to be about 30%, while the moisture content of wood particles is less than 10%. The difference is that the smoke produced by burning particles is significantly reduced. Second, the pellets produce less ash, which is removed during the pelleting process due to soil and bark. Third, and most importantly, energy density. The energy density of wood pellets is more than 3 times larger than wood chips.