Osburn Soho Installation and Operation Manual
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tend the wood fire and should provide enough heat for four hours or more. Small fires like this are
a good time to use softer wood species so there will be less chance of overheating the house.
4.3.6.2
Long Lasting Low Output Fires
Sometimes you will want to build a fire to last up to eight hours, but don’t need intense heat. In
this case use smaller pieces of hardwood and place the logs compactly in the firebox so the pieces
are packed tightly together. You will need to fire the load hot for long enough to fully char the log
surfaces before you can turn the air down. Make sure the fire is flaming brightly before leaving the
fire to burn.
4.3.6.3
High Output Fires for Cold Weather
When the heat demand is high during cold weather, you’ll need a fire that burns steadily and
brightly. This is the time to use your biggest pieces of hardwood fuel if you have it. Put the biggest
pieces at the back of the firebox and place the rest of the pieces compactly. A densely built fire like
this will produce the longest burn your wood fire is capable of.
You will need to be cautious when building fires like this because if the air is turned down too
much, the fire could smoulder. Make sure the wood is flaming brightly before leaving the fire to
burn. The wood should be positioned in a north/south fashion, that is, from the front to the back
of the firebox.
4.3.6.4
Maximum Burn Cycle Times
The burn cycle time is the period between loading wood on a coal bed and the consumption of
that wood back to a coal bed of the same size. The flaming phase of the fire lasts for roughly the
first half of the burn cycle and the second half is the coal bed phase during which there is little or
no flame. The length of burn you can expect from your wood fire, including both the flaming and
coal bed phases, will be affected by a number of things, such as:
•
firebox size,
•
the amount of wood loaded,
•
the species of wood you burn,
•
the wood moisture content,
•
the size of the space to be heated,
•
the climate zone you live in, and
•
the time of year.
The table below provides a very general indication of the maximum burn cycle times you are likely
to experience, based on firebox volume.
FIREBOX VOLUME
MAXIMUM BURN TIME
< 0.042 cubic meter
3 to 5 hours
0.042 m
3
to 0.056 m
3
5 to 6 hours
0.056 m
3
to 0.071 m
3
6 to 8 hours
0.071 m
3
to 0.085 m
3
8 to 9 hours
> 0.085 m
3
9 to 10 hours
Long burn times are not necessarily an indication of efficient wood fire operation. When you are
home during the day and able to tend the fire, it is preferable to build a smaller fire that might
provide three or four hours of heating than to fully load the firebox for a much longer burn.
Shorter burn cycles make it easier to match the heat output of the wood fire to the heat demand
of the space.
