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Version 2.0b 53
As a final note, the four basic stages of wood burning are:
a) Up to 212
o
F the wood is boiling of the moisture.
b) Near 575
o
F gasification of the solid wood fuel occurs. The wood will simply seem to
disappear. Very little energy is released in these first two stages and external energy
must be applied to sustain any combustion that is occurring.
c) Somewhere between 900
o
F and 1100
o
F the wood fuel particles have combined with
oxygen molecules and released the majority of the available energy. Some gases will still
not have reached ignition temperature and at this critical stage, if too much heat is
removed from the combustion chamber, no more fuel will be burnt. All remaining fuel
will simply exhaust through the system as unburned material.
d) At temperatures around 1500
o
F the remaining gases and tars will burn off in the
combustion chamber. This final combustion yields an additional 10 to 20% additional
heat energy and gives a very clean final exhaust from the product.
Wood pellets, as compared to wood logs, enhance the amount of energy released during the burn cycle
because of the uniformity of product, the reduced moisture content, and the variation in materials used to
produce the wood pellet. These variations allow the turbulence in the burn system to ensure a better
agitation of fuel with air and a more rapid and efficient burn. As other biomass fuels are utilized,
optimum mixes of pellets will ensure clean burning, reduced emission system are available that compete
favorably in the consumer market.
The service technician must be aware that as technology evolves, all stove manufacturers will strive to
control more of the variables that might adversely affect the combustion process. In addition, stove
manufacturers will strive to optimize the efficiency of the products burn process. It is the service
technician’s responsibility to understand not only the particular product but also how environmental
issues beyond the control of both the manufacturer and the service technician can affect a product’s burn
process. This understanding will make trouble diagnosis less time consuming and more accurate for all
parties involved in maintaining the product in a reliable manner to the satisfaction of our mutual
customers.