Vermont Casting 1610 User Manual

29

transfer, and it gives you long-term flexibility for install-
ing a different stove 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 exhaust enough to cause draft and 
creosote problems. With prefabricated chimney, bring it 
down to six to eight feet from the stove. With a masonry 
chimney, arrange the pipe so that it turns into the chim-
ney within eight feet of the stove. 

Each ‘airtight’ stove requires its own flue. If an airtight 
stove is vented to a flue that also serves an open fire-
place, or a leakier stove, it’s easier for the chimney draft 
to pull air in through those channels and performance 
of the stove suffers. Imagine a vacuum cleaner with a 
hole in the hose to understand the effect here. In some 
cases the other appliance can even cause a negative 
draft through the stove, and result in a dangerous draft 
reversal.

Creosote is a by-product of slow wood-burning. It’s an 
organic tar that can condense in the flue if it is pres-
ent in the exhaust, slow-moving, and cools to less than 
290°F (130°C). 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 that will encourage 
good draft and minimize creosote production.
Because letting the exhaust cool off and slow down 
is one of the keys to creosote accumulation, 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 (NFPA) recom-
mends a chimney liner 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 guide-
lines as part of their building codes.

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. ‘Green’ wood has a lot of moisture in it; it will 
burn, but some of the heat potential is used to boil the 
extra moisture from the wood. This reduces the amount 
of heat 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 ap-
pearance 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, wood can be too dry and too 
volatile. Smoke and combustible gases can ‘gas out’ 
from the wood quickly and densely enough to overload 
the combustion system. If you hear a rumbling or roar-
ing noise (like a propane torch) from the stove, that is a 
sign that the stove is overfiring.  

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 until they 
are concentrated enough and hot enough to ignite. If 
your stove back-puffs, the stove needs to cool down. 
You should open the damper to let the smoke rise to 
the flue more quickly, allow more air into the firebox, 
avoid big loads of firewood and check that the wood 
moisture is not too low.  

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 awhile 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. 

Good draft also depends on a supply of air to the 
stove; a chimney can’t pull in more air than is avail-
able 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 air consuming equipment. If you 
need to crack a nearby window or door to enable the 
chimney to flow well, it may be a good idea to install an 
outside-air intake to bring combustion air directly to the 
stove. An outside air kit is available to connect the stove 
directly to a source of outdoor combustion air.