Wood Pellet Traits and Common Characteristics

Although the chemical constituents and moisture content of different biomass materials vary, there are common characteristics that include:
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; and

Ash content - important factor in maintenance frequency.

Standard vs. Premium Grade Fuel

In 1995, the Pellet Fuel Institute established national standards for residential pellet fuels. All of the measurable characteristics are the same for both fuel grades except ash content. Standard grade pellet fuel with up to 3% ash content is usually derived from materials, which result in more residual ash, such as sawdust containing tree bark. Standard pellets should only be used in stoves designated for their use.

Premium grade, pellet fuel with less than 1% ash content is usually produced from hardwood or softwood sawdust containing no tree bark. Ash content varies in premium fuels from about .3% in some western softwoods to about .7% in eastern hardwoods. Premium pellets, which make up over 95% of current pellet production, can generally be burned in stoves calling for either standard or premium fuel.

Increased availability of standard fuel is anticipated as stove designs continue to improve ash tolerance. Ash content determines fuel grade because of its role in maintenance frequency. The prime factor determines maintenance frequency of ash removal from the appliance and venting system. The size of the ash drawer, fuel feed and grate design, proper venting, correct operation and maintenance all play a part in maintenance frequency. The experienced pellet stove professional is the best source of information about stove and fuel compatibility.

What are the differences between types and brands

Differences in pellet fuel include Btu range. For example, Btu (heat) content may range from just under 8,000 to almost 9,000 Btu, depending upon species and region of the country.

Trace minerals in pellet raw materials vary not only from region to region, but even in close by growing areas. Some trace minerals promote clinkering, the formation of clumps of fused ash that can block air inlets in the burn pot. A fuel's tendency to form clinkers in a stove cannot be predicted by laboratory analysis both because of variations in the raw materials and the different burning conditions that affect the process. Clinkering can increase routine maintenance, but professional recommendations for matching available fuels to stove design can minimize the problem.

Pellet mills strive for consistency despite the nature of the raw material. Slight variations in fuel even from bag to bag are inevitable, but the differences are usually insignificant and much smaller than found in the original raw material before processing.