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Vermont Castings Intrepid Multi-Fuel
2000970
- so use whatever combination of installation 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 moisture 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 overfir
-
ing. 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.
Backpuffing
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 stabi-
lize, then see whether you can vary the strength of the fire
by swinging the air control open and closed. Results 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 burn-
ing 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 competition
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.
In many cases, local or national codes require the installa-
tion of permanently open air vents, particularly with larger
appliances (i.e. above 5 kW). Refer to these codes to
determine specific requriements for your installation.
Conclusion
Woodburning 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.