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7
2012-11
Chimney renovation
SH Operation
Chimney renovation
Chimney renovation
With its controlled induced-draught fan and
adjustable minimum exhaust gas temperature,
your new boiler will largely adjust to existing flues
without the need for any special measures. Never-
theless, you should have the suitability of your flue
checked by a chimney sweep or chimney builder.
If the draught exceeds 30 Pa in very tall flues, a
draught-regulating damper is required.
Modern heating boilers are more efficient than
older ones and thus produce smaller amounts of
exhaust gas at considerably lower exhaust gas
temperatures.
Flues with "too large a cross-section" in particular
are no longer heated adequately. The moisture
contained in the exhaust gases condenses in the
flue and leads to very slow but inexorable destruc-
tion of old masonry chimneys.
Furthermore, if the diameter of the flue is too large,
the exit velocity and temperature are too low. The
exhaust gas does not have enough energy to rise
and, in extreme cases, the smoke can flow down
the roof.
If your flue does not have a water-resistant liner or
its diameter is too large, it will need to be reno-
vated with the addition of a moisture-insensitive
inner lining. If the existing flue cross-section is
adequate, a ceramic liner that is also resistant to
chimney fires is preferable to a stainless steel liner
when burning wood.
In the case of short flues that are not resistant to
moisture, it may suffice to raise the lower limit
for the exhaust gas temperature to 180°C in the
boiler's control system. In addition an auxiliary
air damper will help to keep the flue dry. If these
measures are deemed satisfactory, the flue should
be inspected to check whether it actually remains
dry. This is best discussed with the chimney sweep.
Also keep in mind that chimneys have a limited
service life. 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.