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ITALY
Built IN
7095401 Rev.03 – EN
19
5. FLUE
Essential requirements for a correct operation of the device:
• the internal section must be preferably circular;
•
be thermally insulated and water-proof and produced
with materials suitable to resist to heat,
•
combustion products and possible condensates;
• not be throttled and show a vertical arrangement with
deviations not greater than 45°;
• if already used, it must be clean;
• observe the technical data of the instructions manual;
Should the flues have a square or rectangular section, internal
edges must be rounded with a radius not lower than 20 mm. For
the rectangular section, the maximum ratio between the sides must
be
≤
1.5.
A too small section causes a decrease of the draught. It is
suggested a minimum height of 4 m.
The following features
are FORBIDDEN
and therefore they
endanger the good operation of the device: asbestos cement,
galvanized steel, rough and porous internal surfaces. Picture 4
gives some examples of execution.
The minimum section must be 4 dm
2
(for example 20 x 20 cm)
for devices whose duct diameter is lower than 200 mm or 6.25
dm
2
(for example 25 x 25 cm) for devices with diameter greater
than 200 mm.
The draught created by the flue must be sufficient, but not
excessive. A too big flue section can feature a too big volume to be
heated and consequently cause difficulties in the operation of the device; to avoid this, tube the flue along
its whole height. A too small section causes a decrease of the draught.
The flue must be properly spaced from any flammable materials or fuels through a proper
insulation or an air cavity.
It is forbidden to let plant piping or air feeding channels pass in the same flue. Moreover, it is forbidden to
create movable or fixed openings on the same for the connection of further other devices.
5.1. CHIMNEY CAP POSITION
The draught of the flue depends also on the suitability of the chimney cap.
Therefore, if it is handicraft constructed, the output section must be more than twice as big as the internal
section of the flue.
Should it be necessary to exceed the ridge of the roof, the chimney cap must assure the discharge also in
case of windy weather (Picture 5).
The chimney cap must meet the following requirements:
• have internal section equivalent to that of the stack.
• have a useful output section twice as big as the flue internal one.
• be manufactured in such a way as to prevent the penetration of rain, snow, and any other foreign
body in the flue.
• be easily checkable, for any possible maintenance and cleaning operation.
Picture 4
Picture 5
(1) AISI 316 steel flue with double
chamber insulated with material resistant
to 400°C.
Efficiency 100% excellent.
(2) Refractory flue with double insulated
chamber and external coating in
lightweight concrete.
Efficiency 100%
excellent.
(3) Traditional clay flue square section
with cavities.
Efficiency 80% excellent.
(4) Avoid flues with rectangular internal
section whose ratio differs from the
drawing.
Efficiency 40% poor.
A+1/2
A
Max.
A+1/2A
(3)
(1) (2)
(4)
(1)
Industrial chimney
cap with pre-fabricated
elements – it allows an
excellent discharge of the
smokes.
(2)
Handicraft chimney
cap. The right output
section must be at least
twice as big as the
internal section of the flue
(ideal value: 2.5 times).
(3)
Chimney cap for steel
flue with internal cone
deflector of smokes.