25
Save These Instructions
Vermont Castings • Aspen 1920 Owner's Manual_R32 • 08/17
Flue Sizing:
The flue size for a controlled-combustion appliance should
be based on the cross-sectional volume of the stove flue
outlet. In this case, more is definitely not better. Hot gases
lose heat through expansion; if a stove with a six-inch flue
collar (28 square inch area) is vented into a 10” x 10” flue, the
gases will expand to over three times their original volume.
As gases cool with expansion, draft strength decreases. If an
oversized flue is also outside the house, the heat it absorbs
will be conducted to the outdoor air and the flue will remain
relatively cool.
It is common for a masonry flue to be oversized for the
stove. Such a chimney can take quite a while to warm up
and the stove performance will likely be disappointing. The
best solution to an oversize flue problem is the installation
of an insulated steel chimney liner of the same diameter as
the appliance flue outlet. The liner keeps the exhaust gas
warm and the result is a stronger draft. An uninsulated liner
is a second choice - although the liner will keep the exhaust
restricted to its original volume, the air around the liner will
require time and heat energy to warm up.
Check your local codes. You may be required to install a flue
liner in any oversize or masonry flue.
Pipe & Chimney Layout
:
Every bend in the flue will act as a brake on the exhaust as
it flows from the firebox to the chimney cap. The ideal pipe
and chimney layout is straight up from the stove through a
completely straight chimney. Use this layout if at all possible
as it will promote optimum stove performance and simplify
maintenance.
If the stovepipe must elbow to enter a chimney, locate the
elbow about midway between the stove top and the chimney
thimble. This configuration lets the smoke speed up before it
must turn, keeps some pipe in the room for heat transfer, and
allows long-term flexibility for installing a different appliance
without relocating the thimble.
There should be no more than eight feet of single-wall stove
pipe between the stove and a chimney. Longer runs can cool
the smoke enough to cause draft and creosote problems.
Use double-wall stove pipe for longer runs.
Single Venting:
Your stove requires a dedicated flue. Do not connect the
stove to a flue used by any other appliance. Chimney draft
is a natural form of energy and follows the path of least
resistance. If the stove is vented to a flue that also serves
an open fireplace or another appliance, the draft will also
pull air in through those avenues. The additional air flow will
lower flue temperatures, reduce draft strength and promote
creosote development; overall stove performance will suffer.
The effect is similar to that of a vacuum cleaner with a hole
in the hose. In some extreme instances, the other appliance
can even impose a negative draft and result in a dangerous
draft reversal.
Fuel
:
Even the best stove installation will not perform well if poor
fuel is used. I available, always use hardwood that has been
air-dried (‘seasoned’) 12-18 months. Softwood burns more
rapidly than hardwood and has a high resin content conducive
to creosote production. Decayed wood of any type has little
heat value and should not be used.
All unseasoned (‘green’) wood has a high moisture content.
Much of its heat value will be used to evaporate moisture
before the wood can burn. This significantly reduces not only
the amount of energy available to warm your home, but also
the intensity of the fire and temperature of the exhaust gas.
Incomplete combustion and cool flue temperatures promote
creosote formation and weak draft.
You can judge the moisture content of wood by its appearance
and weight or use a commercially available moisture meter
for an exact measurement. Unseasoned wood will be a third
heavier than dry wood. Also, look for cracks (‘checking’) in
the ends of the log that result from contraction as the wood
dries. The longer and wider the cracks, the dryer the wood
is. Purchase your fuel from a reputable dealer.
Creosote:
Creosote is a by-product of low-temperature stove operations,
weak draft or both. It is a tar that results when unburned gases
condense inside the flue system at temperatures below
290°F. Creosote is volatile and can generate chimney fire. All
of the installation characteristics that adversely affect chimney
draft also promote creosote condensation. Consequently,
you can minimize creosote accumulation with an effective
chimney design and the use of operational techniques that
encourage good draft and complete combustion.
Backpuffing:
Backpuffing is a condition that results when the draft is too
weak to pull flue gases out of the chimney system as fast
as the fire is generating more. Volatile gases build up within
the firebox until reaching a density and temperature at which
they ignite. With this ignition, you may hear a muffled popping
sound and see a bit of smoke forced out of the air inlets.
This condition is most likely to occur in the spring or fall
when moderate outdoor temperatures and low intensity
fires combine to inhibit draft strength. If your stove backpuffs
open the air inlets to induce a livelier fire and speed airflow
through the stove. Avoid large loads of firewood at one time.
You should always see lively, dancing flames in the firebox; a
lazy, smoky fire is inefficient and will promote draft problems.