Crown Royal Stoves RS7300MP, Installation, Operation & Maintenance Manual, Page: 36 / 58

Burning materials not recommended by the manufacturer can play a major role in visible emissions.
Materials such as plastics, garbage, rubber tires, and even wood products such as cardboard and paper that may
be coated with petroleum products may emit excessive smoke.
Fire starters such as gasoline, oil, and other chemicals can also make an ordinary wood fuel load seem very dirty
once burned. If people who own outdoor furnaces start fires with some kindling and load with wood fuel as
recommended above, they can eliminate a lot of the smoke that others see and the problems that go with it.
5.
Loading
The amount of wood loaded into an outdoor furnace in relation to the firebox size also has an effect on
visible emissions. For every size of wood load there is a minimum amount of space needed to complete the
combustion process. For instance, if a person were to load a relatively small firebox completely and load a larger
firebox with the same amount of wood, with all of the other factors being the same, the larger firebox would burn
cleaner. In the smaller firebox, the combustion process does not have enough room to expand, heat up, and mix
before exiting the firebox (insufficient time, temperature, and turbulence). Just because a firebox is large does not
mean that it should be filled completely. This large volume is used in part for what happens AFTER it is loaded.
B.
Furnace Size
The size of a furnace should be large enough to provide sufficient heat without constant reloading. If the
target burn time is 12 hours, an adequately sized furnace will provide enough heat for 90% of all heating days.
There will always be the extraordinarily cold days for which no one can plan. A small furnace that needs constant
reloading will unavoidably be left unattended and will lose much of its available heat. In these situations, the
firebox is left relatively cold and restarting will be dirtier because of flame quenching on the cool firebox walls. A
good rule to follow is be that if the furnace cannot stay within 20% of its set point under regular reloading, then it
is undersized and a larger furnace is needed.
C.
Chimney Considerations
Although chimney height has little to do with overall emissions, it should be considered in ALL
installations of outdoor furnaces. Installers and dealers should first take a look at the proposed location and take
a few things into account. Location of nearby buildings, structures, and natural geography all affect the furnace’s
ability to draft. While higher is generally better, it is sometimes tough to convince the furnace owner to add
length to the chimney because of the extra cost.
VI.
Conclusions
The proper use of an outdoor furnace can significantly reduce the visible emissions that it produces.
Simple fuel considerations with regard to moisture content, size, and amount help hinder the production of smoke
and ultimately help improve efficiency. Other obvious ways to
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