Vermont Casting 2477 用户手册

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Your stove is only one part of a system that includes the 
chimney, the operator, the fuel, and the home. The other 
parts of the system will affect how well the stove works. 
When there is a good match between all the parts, the 
system works well. 
Wood stove operation depends on natural (unforced) 
draft. Natural draft occurs when exhaust gas is hotter 
(and therefore lighter) than the outdoor air at the top of 
the chimney. The greater the temperature difference, the 
stronger the draft. As the hot exhaust gas rises out of 
the chimney, it generates suction that draws air into the 
stove for combustion. A slow, lazy fire when the stove’s 
air inlets are fully open indicates a weak draft. A brisk fire, 
supported only by air entering the stove through the air 
inlets, indicates a good draft. The inlets are passive; they 
regulate how much air can enter the stove, but they don’t 
force air into it. 
 The efficiency of a modern woodburning appliance, 
(in which the amount of air available for combustion is 
regulated), depends on the chimney to keep exhaust 
gases warm all the way outdoors. The characteristics 
of your chimney - whether it is steel or masonry, interior 
or exterior, matched or mismatched to the stove outlet, 
- determine how quickly it will warm up and how well it will 
sustain the optimum temperatures necessary to main-
tain strong draft and efficient combustion. Here follows a 
description of various flue system characteristics and the 
related effects on stove performance.

Although masonry is the traditional material used for 
chimney construction, it can have distinct performance 
disadvantages when used to vent a controlled-combus-
tion woodstove. Masonry forms an effective ‘heat sink’ - 
that is, it absorbs and holds heat for long periods of time.
The large mass, however, may take a long time to be-
come hot enough to sustain a strong draft. The larger the 
chimney (in total mass), the longer it will take to warm up. 
Cold masonry will actually cool exhaust gases enough 
to diminish draft strength.  This problem is worse if the 
chimney is located outside the home or if the chimney 
flue has a cross-sectional volume much larger than the 
stove outlet. 

Most factory-made ‘Class A’ steel chimneys have a layer 
of insulation around the inner flue. This insulation keeps 
the smoke warm and protects the surrounding structure 
from the high flue temperatures. Because the insulation 
is less dense than masonry, the inner steel liner warms 
up more quickly than a masonry chimney; this makes 
the steel chimney support a good draft more quickly than 
masonry does. Steel chimneys are not as attractive as 
masonry, but they are very durable and generally outper-
form masonry. 

Because the chimney’s function is to keep the smoke 
warm, it is best to locate it inside the house. This location 
uses the house as insulation for the flue and allows some 
radiant heat release from the flue into the home. Since 
an interior chimney doesn’t continuously lose its heat to 
the outdoors, less heat from the stove is required to get it 
warm and keep it warm.

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 instal-
lation 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.

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 perfor-
mance 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.