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The exhaust duct of the combustion products, generated by the forced draught unit, must meet the
following requirements:
Be airtight to combustion products, waterproof, and properly insulated according to the
conditions of use (see UNI 9615);
Being made of materials suitable to resist normal mechanical stress, heat, action of the
combustion products, and condensate if any;
Have ascending development after the vertical tract for the entire remaining path with a
5% minimum slope. The sub-horizontal development part must not have a length greater
than ¼ of the effective height of the flue or chimney, and in any case not be longer than
2,000 mm;
Have a preferably circular internal section: square and rectangular sections should have
rounded corners with a radius larger than 20 mm;
To have constant, free and independent internal section;
To have rectangular sections with a 1.5 maximum ratio between sides;
If the flue is installed outdoors or in a cold room (e.g. boiler room) it is absolutely
necessary that it is insulated to prevent cooling of the fumes and the formation of
condensate;
To mount exhaust channels (stretching from the unit to the flue inlet), elements of non-
combustible materials suitable for resisting combustion products and any condensation
must be used;
It is forbidden to use fibre cement pipes to connect the appliances to the flue;
Exhaust channels must not pass through rooms in which the installation of combustion
appliances is forbidden;
When mounting exhaust channels, make sure they are flue gas sealed;
Installation of horizontal sections should be banned
;
The usage of elements in counter-slope is forbidden;
The exhaust channel must allow soot recovery or cleaning using a swab, and must have
a constant section;
It is forbidden to run other air supply channels and pipes for plant engineering use into the
exhaust channels, even if oversized.
The
chimney
is a device crowning the flue, used to facilitate the dispersion of combustion products.
It must meet the following requirements:
Have a useful outlet section not smaller than twice that of the flue on which it is inserted;
Be shaped so as to prevent the penetration of rain and snow into the flue;
Be built in such a way that combustion discharge is ensured even in case of wind in any
direction and angle.
The outlet height (where height corresponds to the top of the flue, regardless of any chimneys) must
be beyond the so-called reflow area in order to avoid the formation of counter-pressures preventing
the free discharge of combustion products into the atmosphere.
It is therefore necessary to ensure compliance with the minimum heights shown in the following
figures:
Technical
volume
0
,5
m
0
,5
m
Dista nce > 5 m
Dista nce < 5 m
Distanc e> 1,85 m
Distanc e< 1,85 m
0
,5
m
o
v
e
r
th
e
r
id
g
e
Reflow zone
1
m
m
in
im
u
m
1
5
°
