What are the common characteristics of pellets? Although the chemical constituents and moisture content of different biomass materials vary, the Pellet Fuels Institute (PFI) has identified common characteristics and developed fuel standards. These voluntary industry standards assure as much uniformity in the final product as is possible for naturally grown materials that become processed, but not refined fuel. PFI graded fuel must meet tests for: Density: consistent hardness and energy content (minimum 40 pounds/ cubic foot) Dimensions: length (1 1/2" maximum) and diameter (1/4"or 5/16") to assure" predictable fuel amounts and to prevent fuel jamming Fines: limited amount of sawdust from pellet breakdown to avoid dust while loading and problems with pellet flow during operation (amount of fines passing through 1/8" screen no more than .5% by weight)" Chlorides: limited salt content (no more than 300 parts per million) to avoid stove or vent rusting Ash content: important factor in maintenance frequency.