Hearthstone Quality Home Heating Products, Inc.
Heritage Model 8090 Pellet Stove
Page 52 of 53
2.2 LABELING
PFI Fuel Standards recommend that manufacturers identify their product with a guaranteed analysis
and parameters included in the label (example below).
3. EFFECTS ON PERFORMANCE AND MAINTENANCE
When compared to cordwood on a one to one basis, pellets offer some distinct advantages. Pellets are more
consistent and predictable in moisture and Btu content. They are more compact, so they require less storage
space. They are cleaner, easier to handle, and they burn cleaner. However, these characteristics have to be put
into the perspective of the appliances they burn in to have real meaning. Pellet fuels narrow the wide variables
of cordwood fuels, but pellet appliances, as mechanical, electrical based systems, also have a narrower range
of fuel tolerance than wood stoves. Understanding the effects of fuel characteristics in pellet appliances is
essential for optimum performance, adequate maintenance, and overall customer satisfaction.
3.1 PERFORMANCE
As will be discussed later, different appliance designs have different fuel requirements and tolerances.
For now, we can look broadly at some effects of using unsuitable or impure fuel.
3.1.1 COMBUSTION
A direct effect of fuel quality on combustion that is not included in the PFI Standards is silica
content. Silica is essentially sand or dirt that is naturally in the bark of the tree or that enters the feed
stock in the handling process. In the combustion process, silica is heated to fusion temperatures,
melts, and solidifies as it is cooled. The result is clinkers, solid chunks of lava like material. The
effect on combustion occurs if the clinkers stay in the grate area and block incoming combustion air.
Analysis of silica content is impractical because of the variations in growing conditions and because
of the significant effect on fusion temperatures of small amounts of trace elements. The normal
melting point of silica, 2,700° F., is reduced to 1,500° F. in the presence of minute amounts (1/4%)
of alkaline salts (sodium chloride or potassium chloride).This reduction in the melting point promotes
ash fusion at lower temperatures and increases clinkering. Combustion temperatures in the burn
pot/grate area vary widely with appliance design, so fuel with silica may cause clinkering problems
in a stove with high combustion chamber temperatures and not in another appliance that operates
with lower temperatures.
Ash content has indirect effects on combustion. Excessive ash content, if not maintained properly,
can restrict or block burn pot air holes and/or the venting system and result in poor combustion due
to inadequate combustion air.
Improper pellet density can also have a direct effect on combustion by causing an abnormal feed
rate. Low density pellets may feed too little combustible fuel and may cause the fire to go out, while
excessively high density pellets can be difficult to start in automatic ignition appliances or they can
