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Chimney

Information for installation

the combustion chamber temperature doesn't fall, the
wood  continues  to  gasify.  Unburned  wood  gas
condenses to tar in the chimney, which can be ignited
by sparks from the fire.
With  modern,  lambda-controlled  wood  boilers,  soot
fires of this kind are virtually impossible, as the control
system restricts wood gasification, not the air. In mod-
ern,lambda-controlled  wood  boilers,  the  control
system shuts down the fire by stopping the fuel supply,
without closing off the supply of air to the fire. This way,
there  is  no  lack  of  air  and  no  flammable  tar  in  the
chimney. In addition, the low flue gas temperatures of
modern wood  boilers  also  provide no  ignition source
for a soot fire. Modern and properly maintained wood
boilers  therefore  pose  no  danger  to  chimneys  from
soot fires.

Moisture-resistant W3G flue systems

Since  2005,  W3G  chimneys  (classified  according  to
the German DIN 18160) exist that 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.

Flue pipe to chimney preferably stainless steel

Due to the low flue gas temperatures, we recommend
that the flue gas pipe from the boiler to the chimney is
made of a stainless steel flue duct that is not sensitive
to moisture.

Provide a short, ascending flue pipe to the
chimney

The flue pipe from the boiler to the chimney must be
short, leakproof and ascending. "Attractive" right-angle
flue offsets with two or more bends are bad in a flue
pipe. The optimum to strive for is the shortest pipe from
the boiler to the chimney with a minimum of directional
changes.  The  flue  pipe  to  the  chimney  must  be
leakproof. Use heat-resistant silicone as a sealant for
unsealed  sleeve  pipes.  Otherwise,  you  can  expect
smoke  to  escape  into  the  boiler  room  as  the  boiler
heats up. The flue pipe must always be laid so that it
ascends towards the chimney.
Long horizontal flue pipes to the chimney must have a
narrow cross-section and above-average insulation (>
50 mm). Provide enough cleaning openings in the flue
pipe. A  flue  pipe  to  the  chimney  with  a  large  cross
section would reduce the calculated required chimney
cross section. However, ash deposits will form at low
flow  speeds,  and  the  theoretically  calculated  flue
draught will be lost again.

With a large chimney cross-section, a maximum
straight length of the flue pipe up to half the effective
chimney height is possible (calculation required).

Connection to the sewage system for the chimney

For the condensate in the chimney, a connection to the
sewage system (e.g. duct) with at least DN25 via a
siphon is required. The sewer pipe to which the con-
densation drain pipe is connected should be flushed
once a year.

Fig. 7-1: Condensate drain

For chimneys on the outer walls (made of
stainless steel, for example), frost-proof run-off

must be provided for the condensate water.

Insulate flue pipe to chimney

The flue pipe from the boiler to the chimney should be
insulated with at least 30 mm, preferably 50 mm, of
mineral wool to avoid temperature losses, which can
lead to a build-up of condensation.

Prevention of structure-borne noise

There should not be a fixed connection between the
flue pipe and the chimney to prevent structure-borne
noise as much as possible! Good flue gas systems are
acoustically insulated. If steel pipes are connected to a
fireclay chimney, ceramic fibre bandages have proven
effective at preventing structure-borne noise as well as
damage to the fireclay sleeve.