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Intrepid II Woodburning Stove
2000966
Creosote
Creosote is a by-product of slow wood-burning. It’s an
organic tar that can condense in the flue if it’s dense
in the smoke, and slow-moving, and cools off to less
than 290°F. Condensed creosote is volatile, and can
generate chimney fires if it gets hot enough. All the
features that affect chimney draft also affect creosote
condensation - so use whatever combination of installa-
tion features and operational steps will encourage good
draft and minimize creosote production.
Because letting the smoke cool off and slow down is
one of the keys to creosote production, it makes sense
to line a chimney to match the stove’s outlet size, for
safety reasons as well as performance. Canadian law
requires a matching liner to serve any stove or insert
vented through a fireplace chimney; in the US, the
National Fire Protection Association recommends one if
the flue is more than three times bigger (in square area)
than the outlet on the stove or insert. Some localities
enforce the NFPA guidelines as part of their building
codes.
Fuel
Even the best stove installation will not perform well
with poor fuel. The best fuel is hardwood that has air-
dried 12-18 months. Softwood burns, but not as long as
hardwood. Fairly ‘green’ wood has a good amount of
moisture in it; it will burn, but some of the heat potential
is used to drive the remaining moisture off the wood.
This reduces the amount that reaches your home and
can contribute to a creosote problem. There are mois-
ture meters available for firewood; you can also judge
your wood by its appearance and weight. If you get it
green, lift a piece and get a sense of its weight; it can
lose a third or more of its weight as it dries. Also look at
the ends of a log; as it dries it shrinks and often cracks.
The more weathered and cracked a piece is, the drier
it is.
Dry wood burns readily with a good chimney draft. But
with modern stoves, especially catalytic ones, the wood
can be too dry. While extra-dry wood has little creosote
in it, the remainder can ‘gas out’ from the wood quickly
and densely enough to overload the catalytic burner.
If you hear a rumbling or roaring noise, like a propane
torch, from the stove, that is a sign that the catalyst is
seriously overfiring. The catalyst is a platinum film on a
ceramic base; the metal can get to higher temperatures
than the ceramic can take, and overfiring the catalyst
can break it. Dry wood can also burn out faster than
you want. If your dry wood burns out too quickly or
overloads the catalyst you can mix in greener wood to
slow the fire down.
Back-puffing
Back-puffing results when the fire produces volatile
gases faster than the chimney draft pulls them out of
the firebox. The gases back up in the firebox till they’re
dense enough and hot enough to ignite. If your stove
back-puffs, you should open up the damper to let the
smoke rise to the flue more quickly, let more air into
the firebox, and avoid big loads of firewood. Run your
stove with enough primary air so that you always see
lively, dancing flames in the firebox; a lazy, smoky fire is
inefficient and can contribute to creosote buildup in the
chimney.
Draft Testing
An easy way to test your chimney draft is to close the
stove’s damper, wait a few minutes to let the airflow
stabilize, then see whether you can vary the strength of
the fire by swinging the air control open and closed. Re-
sults are not always instant; you may need to wait a few
minutes for a change in the air control setting to have
an effect on the fire. If there’s no change, then the draft
isn’t strong enough yet to let you close the damper, and
you’ll need to open it for a while longer and manage the
fire with the air inlet until the draft strengthens. If you
keep track of your burning habits and relate them to
their effects on the stove’s operation, you’ll be rewarded
with good performance and a safe system.
Negative Pressure
Good draft also depends on a supply of air to the stove;
a chimney can’t pull in more air than is available to it.
Sluggish draft results when a house is tight enough to
prevent the ready flow of air to the stove, or by competi-
tion between the stove and other equipment that sends
indoor air outside - especially power-driven equipment
like range hoods, clothes dryers, etc. If the chimney
draws well with all other equipment turned off (or
sealed, in the case of fireplaces and/or other stoves),
then you simply need to be careful with timing the use
of the other equipment. If you need to crack a nearby
window or door to enable the chimney to draw well,
that’s a sign that you should install an outside-air intake
to bring combustion air directly to the stove. Vermont
Castings dealers carry adapters to attach to the stove
to connect an air duct for outdoor combustion air.
Conclusion
Wood-burning is an art rather than a science. Once the
stove and chimney system are in place, the stove user
can only vary technique, mostly your timing, to achieve
good results. If you keep track of your burning habits
and relate them to their effects on the stove’s operation,
you’ll be rewarded with good performance and a safe
system.