$TEP 2:
PREPARE THE VENTING $YEYTEM
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,
wail
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.
3 1/4"
x 10" to 6" : 5 ft.
<
3 1/4"
x 10" roof cap
= 24 ft
3 1/4"
x 10" 90 ° elbow
= 25 ft
90°elbow
:
10 ft
3 1/4"
x 10" wall cap
: 40 ft
45°elbow
: 5 ft
Figure 9
3-1/4"
x 10" flat
elbow
:
]Oft
To calculate
the equivalent
length of each duct piece used, see the examples
below.
For 3-1/4"
x 10" SYSTEMS
1 3-1/4"
x 10" 90 ° elbow
=
25 ft.
1Wall
Cap
=
40 ft.
8 feet straight duct
:
8 ft.
TOTAL LENGTH
=
73 ft.
[
Exam _les
For 6" ROUND SYSTEMS
wall cap
90° elbows
|
6ft. --_]_/
transition
_'_'2f_t.
1 transition
:
5 ft.
2 90 ° elbows
=
20 ft.
1Wall
Cap
=
40 ft.
8 feet straight
=
8 ft.
TOTAL LENGTH
=
73 ft.
9