Chimney; Basics - eta SH Installation Manual

Basics

For every boiler a chimney of its own
The better the boiler and the chimney are matched,
the greater the energy of the flue gases leaving
the chimney and thus the certainty that they will
rise into the air from the top. If the diameter is too
large, the chimney will not be heated sufficiently
and the exit velocity and temperature will be too
low. The flue gas then lacks the energy to rise and
in extreme cases, the smoke can sink down along
the roof.
Chimneys with a diameter more than 50% greater
than needed must be renovated to reduce the
diameter.
If a chimney is designed for use with two
simultaneously operating boilers, it may prove to
be oversized for the partial load from only one
boiler. If there is really only one chimney available,
a buffer storage tank can help avoid a too-small
partial load.
Chimney renovation - before it's too late
Compared to older boilers, modern ones are much
more efficient and have lower amounts of flue gas
with considerably lower temperatures. The water
in the flue gas condenses and destroys old masonry
chimney walls, very slowly but also inexorably.
Timely renovation before the chimney wall has
been destroyed can be performed quickly and
easily by inserting a tube. But if the flue gas
condensates have penetrated the mortar joints,
then the entire flue must be dismantled and
rebuilt.
Sewage connection for the chimney
For the condensation that forms in the chimney,
a DN 25 sewer connection via trap is needed. The
resulting amount of water is small. If no sewer
connection is possible, then a bucket that is
checked regularly can also be used.
10
A fan-assisted boiler and a gas-fired boiler
may not be connected to the same chimney
Most gas-fired boilers do not have a sealed air flap
and when the fan-assisted boiler is started while
the chimney is cold, the flue gas is pushed through
the gas boiler into the boiler room. Even a flue gas
damper in the gas boiler's flue pipe will hardly
help since these dampers are not certain to close
with a good seal.
With atmospheric gas boilers, old fireclay chimneys
only stay dry with the gas boiler's overflow
opening. The water from the flue gas condenses
in the chimney. During pauses in firing, air flows
through the overflow opening and dries the
chimney. If this air stream is blocked by a flue gas
damper, the moisture can destroy an old fireclay

chimney.

Fan-assisted boiler and wood-burning stove
on the same chimney - a dangerous combination
This combination is not expressly forbidden, but it
is dangerous.
Every wood-burning stove has an air intake
through which any fan-assisted boiler, whether
oil or wood, will blow flue gas into the living area
through a cold chimney. If the wood-burning
stove's firebox door is not closed and the boiler
is defective at the same time, even acute carbon
monoxide poisoning is possible.
The wood-burning stove needs a significantly
larger chimney cross section, which cannot be
heated by the fan-assisted boiler. Cold flue gas
does not rise from the opening; it sinks and can
reach living quarters through open windows.
It may also be possible to hear the boiler's fan in
the living quarters through the wood-burning
stove.
Clarify with the chimney sweep
In any case, the chimney's suitability should be
clarified with the chimney sweep
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