2.2
Fume
extraction
flue
features
The
main
features
characterising
the
fume
extraction
flue
are
given.
They
are
based
on
what
is
set
out
in
standards
UNI
7129
and
UNI
10683/98:
‐
Inspection
valves
(I);
‐
Minimum
height
of
the
pipe
directly
connected
to
the
heater
fume
extraction
outlet
must
be
between
2
‐
3
m;
‐
If
it
is
necessary
to
have
a
horizontal
section,
it
is
advisable
to
make
it
with
a
maximum
length
of
1.5
m
and
with
an
incline
of
3
‐
5%
in
order
to
help
the
fumes
to
escape;
‐
Use
of
a
cowl
that
is
wind
‐
resistant
and
rain
‐
resistant
in
order
to
avoid
a
change
in
the
slight
condition
of
overpressure
the
flue
is
in,
(it
is
strongly
recommended
not
to
use
a
horizontal
section
at
the
end
of
the
flue).
The
reduction
in
pressure
in
the
flue
is
necessary
so
as
to
help
the
normal
flow
of
fumes
from
the
combustion
chamber
towards
the
outside,
in
the
event
of
a
mains
power
cut.
Remember
that
excess
heat
disposal
is
managed
in
an
optimum
way
from
the
electronic
control
panel
(modulation,
switch
‐
off
stage,
etc.).
‐
Flues
must
be
made
of
appropriate
materials
to
resist
combustion
products
and
condensation
(
the
inspection
valves
should
allow
to
discharge
possible
condensation)
‐
The
flues
must
be
manufactured
in
order
to
insure
the
maximum
smoke
resistance
(regulation
UNI
10683/98)
‐
Duct
insulation
particularly
on
the
outside
part
exposed
to
the
weather.
Avoid
making
completely
horizontal
sections.