Vermont-casting 1610 Manuel d'utilisateur télécharger pdf (Page 28)

Defiant 1610 Non-Catalytic Woodburning Stove

30002850

A stove is part of a system, which 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 or insert operation depends on natural

(unforced) draft. Natural draft occurs when the exhaust

is hotter (and therefore lighter) than the outdoor air at

the top of the chimney. The bigger the temperature

difference, the stronger the draft. As the hot gases rise

through the chimney they provide suction or ‘draw’ that

pulls air into the stove for combustion. A slow, lazy ﬁre

with the stove’s air inlets fully open indicates a weak

draft. A brisk ﬁre, supported only by air entering the

stove through the normal inlets, indicates a good draft.

The stove’s air inlets are passive; they regulate how

much air can enter the stove, but they don’t move air

into it.

Depending on the features of your installation - steel

or masonry chimney, inside or outside the house,

matched to the stove’s outlet or oversized - your

system may warm up quickly, or it may take a while to

warm up and operate well. With an ‘airtight’ stove, one

which restricts the amount of air getting into the ﬁrebox,

the chimney must keep the stove’s exhaust warm all

the way to the outdoors in order for the stove to work

well. Some chimneys do this better than others. Here’s

a list of features and their effects.

Masonry Chimney

Masonry is a traditional material for chimneys, but it

can perform poorly when it serves an ‘airtight’ stove.

Masonry is a very effective ‘heat sink’ - it absorbs a lot

of heat. It can cool the chimney gases enough to dimin-

ish draft. The bigger the chimney, the longer it takes to

warm up. It’s often very difﬁcult to warm up an outdoor

masonry chimney, especially an oversized one, and

keep it warm enough to maintain an adequate draft.

Steel Chimney

Most factory-made steel chimneys have a layer of

insulation around the inner ﬂue. This insulation keeps

the chimney warm. The insulation is less dense than

masonry, so a steel chimney warms up more quickly

than a masonry chimney. Steel doesn’t have the good

looks of masonry, but it performs much better.

Indoor/Outdoor Location

Because the chimney must keep the smoke warm, it’s

best to locate it inside the house. This uses the house

as insulation for the ﬂue and allows some heat release

into the home. An indoor chimney won’t lose its heat

to the outdoors, so it takes less heat from the stove to

heat it up and keep it warm.

Chimney Height

The common wisdom tells us that a taller ﬂue draws

better than a short one. This isn’t necessarily so. If a

chimney is tall enough to meet the safety requirements

of the 2/3/10 foot rule, then adding more height isn’t the

right answer to a draft problem. In fact it could make the

problem worse by adding more mass to the chimney

system, which must be warmed up, a distance from the

heat source (the stove). Don’t make a chimney taller

unless you must in order to meet the safety rules, or un-

less there’s some nearby feature causing a downdraft.

Even then, there are downdraft-preventing chimney

caps available, which are probably the smarter choice.

Flue Sizing

The inside size of a chimney for an ‘airtight’ stove

should match the size of the stove’s ﬂue outlet. When

a chimney serves an airtight stove, more is not better;

in fact, it can be a disadvantage. Hot gases lose heat

faster as they travel slower through a chimney; if we

vent a stove with a six-inch ﬂue collar (28 square inch

area) into a 10 x 10” ﬂue, the gases slow to one third

their original speed. This allows the gases to cool more

rapids, which weakens draft strength. If an oversized

ﬂue is also outside the house, the heat it absorbs gets

transferred to the outdoor air and the ﬂue usually stays

cool.

It is common for a masonry ﬂue, especially one serving

a ﬁreplace, to be oversized for the stove. It can take

quite a while to warm up such a ﬂue, and the results

can be disappointing. The best solution to an oversized

ﬂue is an insulated steel chimney liner, the same diam

eter as the stove or insert’s ﬂue outlet; the liner keeps

the exhaust warm, and the result is a stronger draft. An

uninsulated liner is a second choice - the liner keeps

the exhaust restricted to its original size, but the hot

gases still must warm up the air around the liner. This

makes the warm-up process take longer.

Pipe & Chimney Layout

Every turn the exhaust must take as it travels to the

chimney top will slow it down. The ideal pipe and chim-

ney layout is to vent vertically into a completely straight

and vertical chimney. If you are starting from scratch,

use this layout if possible. If the stovepipe must elbow

to enter a chimney, locate the thimble about midway

between the stove top and the ceiling. This achieves

several goals: it allows the gases to speed up before

they must turn, it leaves some pipe in the room for heat

Draft Management

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Vermont-casting 1610 Manuel d'utilisateur Page 28

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