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Chimney
Small chimney diameter required
Please note that for partial-load operation with flue
gas temperature of only 100°C, the large chimney
cross sections that were previously typical for solid
fuel are no longer optimal. If the cross section is too
large, the flue gas is no longer certain to rise from
the chimney opening and may flow along the roof
and sink to the windows of the living quarters.
Height
Chimney diameter in cm
above
(required minimum diameter)
INSERT TABLE!
boiler
20 kW
room
floor
6 m
18 (16) cm 18 (16) cm
7 m
16 (14) cm 18 (15) cm 18 (16) cm
8 m
15 (13) cm 16 (14) cm 18 (15) cm
9 m
15 (13) cm 15 (13) cm 18 (15) cm
10 m
15 (13) cm 15 (13) cm 16 (14) cm
11 m
15 (13) cm 15 (13) cm 16 (14) cm
12 m
14 (12) cm 15 (13) cm 16 (14) cm
*) For boiler outputs over 30 kW and chimney
heights under 8 m, a chimney joint tilted 45° can
help achieve the required draught of 5 Pa at full
load with acceptable cross-sections (a size smaller
than indicated in the table).
Normally no deflagration damper
The boiler is designed with safety routines in the
control system to prevent deflagrations, so no
deflagration damper (also often called a blowback
flap) is required if the connecting pipe is short and
ascends to the chimney. If a deflagration damper is
needed at high points before descending sections
or at the beginning of a long horizontal section
(L > 20 x D), it must be situated so that people are
not endangered by a deflagration.
SH Montage
30 kW
40 kW
50 kW
60 kW
20 cm*
20 cm*
20 cm*
18 (16) cm
18 (15) cm
18 (15) cm
18 (15) cm
18 (15) cm
Dimensioning, requirements
Obsolete regulations require the wrong chimney
Laws and regulations demand a flue system that is
moisture-resistant for oil and gas and one that is
resistant to soot fires for solid fuels.
Wood is a solid fuel. But in the lower output range,
the temperature of the flue gas can be under 100°C
and condensates can be deposited in the chimney.
So the chimney must be moisture-resistant,
"against regulations". Whoever builds a chimney
resistant to soot fires can then look on helplessly as
the condensate destroys the chimney wall.
Soot fires are possible in natural-draught boilers or
wood-burning stoves regulated by throttling the
air supply. When the wood fire is at full intensity
and the boiler temperature has been reached,
a thermostat closes the air flap. That stops the
combustion, but since the combustion chamber
temperature doesn't fall, the wood continues to
gasify. Uncombusted wood gas condenses to tar in
the chimney; the tar can be ignited by sparks from
the fire.
With modern lambda-controlled wood boilers,
With modern lambda-controlled wood boilers,
such a soot fire is nearly impossible since the
such a soot fire is nearly impossible since the
control system reduces the wood gasification
control system reduces the wood gasification and
and not the air, so there is no lack of air and no
not the air. In modern lambda-controlled pellet
flammable tar in the chimney. The low exhaust
boilers, the control system shuts down the fire
temperatures of a modern boiler also provide
by stopping the pellet supply without closing off
no ignition source for a soot fire. With a modern
the air supply. So there is no lack of air and no
and properly maintained wood boiler, there is no
flammable tar in the chimney. The low exhaust
temperatures of a modern boiler also provide
danger to chimneys from soot fires.
no ignition source for a soot fire. With a modern
and properly maintained wood boiler, there is no
danger to chimneys from soot fires.
Moisture-resistant W3G flue systems
Since 2005 there are W3G chimneys (classified
according to the German DIN 18160), which are
resistant to both moisture and soot fires. These
chimneys are approved for all fuels. Most of these
W3G chimneys have ceramic inner pipes, which
have a significantly longer service life than metal
chimneys due to their acid resistance.
11
2012-11
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