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STEP
2:
PREPARE
THE
VENTING
SYSYTEM
STANDARD
FITTINGS
NOTE:
If
the
existing
duct
is
round,
you
must
use
a
rectangular-to-round
adapter,
with
a
rectangular
3"
extension
duct
installed
between
the
damper
assembly
and
the
adapter
to
prevent
the
exhaust
damper
sticking.
DUCT
LENGTH
The
total
length
of
the
duct
system,
including
straight
duct,
elbows,
transitions,
wall
or
roof
caps
must
not
exceed
the
equivalent
of
140
feet.
For
best
performance,
do
not
use
more
than three
90
degree
elbows.
Below
are
the
standard
fittings
and
their
equivalent
length
in
feet.
1
3
3
1/4"x10"
3
1/4"x10"
roof
3
1/4"x10"
90°
to
6"=5ft.
cap=24tt.
elbow=25ft.
4
5
1
6
7
3
1/4"x10"
3
1/4"x10"
90°
elbow
wail
cap
45°
elbow
flat
elbow
-10ft. =40ft.
-5ft.
=10ft.
Figure
9
To
calculate
the
equivalent
length
of
each
duct
piece
used,
see
the
examples
below.
|!
Examples
For
3
1/4"x10"
SYSTEMS
For
6"
ROUND
SYSTEMS
i
90°
elbows
j}-——
6ft.
——»
wali
cap
3
1/4"x10"
ft.
90°
elbow
«
k—
Bit.
——>|
_wall
cap
iN
4
aft.
'
6"
to
3
1/4"
x
10"
transition
31/4"x10"to6"
transition
=
Sft.
1-90°
elbow
=
25ft.
2-90°
elbows
=
20
ft.
Wall
Cap
=
A0ft.
Wall
Cap
=
40
ft.
8
feet
straight
duct
=
68ft.
8
feet
straight
=
68fit.
TOTAL
LENGTH
=
73
ft.
TOTAL
LENGTH
=
73
ft.
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