Flue Systems - Viessmann Vitocrossal 300 CT3 Technical Manual

2.6 Flue systems

2.6 Flue systems
Flue systems
Current regulations on flue systems state
the following requirements:
H Flue systems must be suitably sized in
terms of their cross-section and height
and, where necessary, also in terms of
their thermal resistance and internal
surface, so that the flue gases are dis
charged into open air in all relevant op
erating conditions and no hazardous
overpressure above that of the accom
modation can occur.
H The flue gases of heating systems for
liquid and gaseous fuels can be intro
duced into chimney stacks or flue duct-
ing.
H Flue ducting on buildings must have a
minimum clearance of 20 cm from win
dows.
Flue systems for condensing boilers
Depending on the heating water return
temperature, the flue gases in the Vito
crossal 300 are cooled down to below the
condensing temperature and leave the
boiler with a relative humidity of 100 %.
The flue gas temperature is between 5 and
15 K higher than the heating water return
temperature. Depending on the conditions
which exist in the system, the flue gas
temperature can therefore range between
30 and 110 ºC.
With the control thermostat set to 75 ºC,
the max. flue gas temperature is 80 ºC.
Due to the low flue gas temperature, the
resulting lower up-draught and the con
tinued condensing of the flue gases in the
flue system, the flue ducting must be
calculated by the manufacturer and con
structed from suitable materials.
Furthermore, special requirements apply
with regard to the constructional design
and installation of flue systems for con
densing boilers.
Condensing boilers should be connected
to tested and approved flue gas ducting.
The flue pipes should be approved in ac
cordance with building regulations.
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H The outlet points of chimney stacks and
flue ducting must
project at least 40 cm above the roof
ridge or be at least 1 metre from the
roof surface.
project at least 1 metre above rooftop
structures or room openings where
the distance from the chimney stack
or flue ducting is less than 1.5 metres.
project at least 1 metre above unpro
tected parts made of combustible ma
terials, with the exception of roofing,
or be at least 1.5 metres away from
these.
Further requirements may have to be
met if additional hazards or excessive
loads are anticipated.
We advise you to consult a competent
person for advice.
Flue gas temperature sensor
Only parts which are a component of the
flue pipe and are tested in accordance
with building regulations may be fitted to
or in the flue pipes of condensing boilers.
At the manufacturing stage, the flue sys
tem should already incorporate openings
in which flue gas temperature sensors
can be installed and which must be tested
together with the flue system.
It is not permitted to drill the flue pipe
and fit other parts afterwards.
Vitocrossal 300 condensing boilers can
also be connected to moisture-resistant
stacks provided the chimney manufac
turer can certify their suitability for the
flue gas values of the boiler in accord
ance with DIN 4705 (see technical data in
the corresponding data sheet).
1.5 m
x
If 1.5 m
x
then a 1.0 m
In an existing or newly constructed stack
(masonry stack without liners), the flue
gas ducting must be run to above roof
level. With regard to the size and design
of the stack, we recommend that you con
sult a flue manufacturer at the planning
stage.