Hearthstone Quality Home Heating Products, Inc.
Heritage Model 8090 Pellet Stove
Page 51 of 53
between parts of the feeding mechanism and may cause feeding jams. It is therefore important to
know whether an appliance manufacturer specifies the size of pellets to be used in a specific
appliance.
2.1.3 FINES
Fines are the smallest, dust-like particles produced in the pelleting process. They also occur in
breakdown during shipping and handling. The production standard is intended to assure hard
pellets that withstand handling. Excessive fines represent loss of usable fuel and cause
performance and maintenance problems. They are also a source of irritation for appliance owners
when the dust escapes into the home during pouring from the bag into the hopper. The fines are
less likely to burn because they are easily blown away from the flame by combustion air. Fines
cause performance problems, including loss of fuel feeding if they build up on the sides of the
hopper and reduce the opening size to the fuel delivery system. Additionally, fines can increase the
need for maintenance by filling ash traps prematurely and by jamming augers.
2.1.4 SODIUM
The presence of excessive salt, specifically water soluble inorganic sodium, can cause severe
damage from corrosion in appliances and venting systems. The sources of salt contamination
include logs that have been floated in salt water, plywood, and particleboard. Manufacturers now
test to ASTM E776, standard for sodium extraction. Additionally, the presence of trace amounts of
alkaline salts can increase clinkering, due to a reduced ash melting point for silica.
2.1.5 INORGANIC ASH
Ash is the term for the various noncombustible minerals that remain after combustion. Ash content
is the basis for determining fuel grade since all other criteria are identical for both premium and
standard grade. Later discussion of appliance design and maintenance requirements will indicate
clearly how crucial this fuel characteristic is. On one hand, fused ash, or clinkers (see discussion
under 3.1.1 Combustion below), can block combustion air inlets and affect performance adversely.
On the other, fly ash that is blown from the fire chamber can accumulate on heat exchangers and in
the venting system with problematic results. Simply put, ash content is the main factor determining
the frequency of appliance maintenance. In some appliances, that frequency can make the use of
higher ash fuels impractical. Predictions of premium quality low ash fuel shortages are consequently
a growing concern that appliance manufacturers are addressing in appliance design.
Appliance sensitivity to ash content varies with design, venting system design, and recommended
maintenance frequency. Even within the allowed 1% ash content of premium grade pellets, there
are noticeable performance variations in some appliances. Changing from a .25% ash content fuel
to a .75% ash content fuel can cause troublesome performance and maintenance in some
appliances. Manufacturer’s fuel recommendations and individual ongoing experience with locally
used fuels are important for appliance adjustment and customer satisfaction. Some biomass and
corn burning appliances have been introduced to deal with the 1-3% ash produced from these fuels.
A fuel stirring/aeration device may be incorporated to mix the ash with the fuel and to increase fuel
efficiency.
2.1.6 LENGTH
Excessively long pellets can cause bridging, the condition of pellets getting stuck across the fuel
delivery entrance of the hopper. The effect is that of a log jam, with fuel unable to feed past the
blockage. Long pellets may also cause auger jams. Finally, long pellets deliver inconsistent
amounts of fuel. Dramatic variations in fuel feed rates in turn causes performance problems since
combustion air settings deliver a volume of air based on expectations of consistent amounts of fuel.
PFI standards call for maximum pellet length of 1 1/2 inches. In spite of this standard, some
appliances will bridge with this length pellet and can be difficult to diagnose. The appliance
manufacturer should be consulted regarding their recommendations for maximum pellet length.