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Simpson Duravent Components only
When using Simpson components a
o
maximum of two 90
o
four 45
elbows are allowed in the
system (these are in addition to the
o
45
elbow off of the top of the
unit). Horizontal runs must be
upwardly sloped at a minimum of a
1/4" (6mm) rise per foot of
horizontal run.
When configuring the vent system
the following equivalent lengths for
elbows should be used in
conjunction with Figure 3.5.
For elbows in a horizontal plane a
o
90
elbow should be treated as 4
equivalent horizontal feet, and a 45
elbow as 2 equivalent horizontal
feet. For elbows in the vertical
o
plane a 90
elbow should be treated
as 2 equivalent horizontal feet, and
o
a 45
elbow as 1 equivalent
horizontal foot. The 45
the back of the units is not to be included in these calculations.
Example 1
The figure below shows an installation in which there is a vertical rise off the back of unit in where two 45
elbows have been employed, followed by a 90
example the equivalent lengths of the 45
have an equivalent horizontal length of 2 feet. If the design of the system is constrained by the horizontal run,
then Figure 3.6 must be used to determine the minimum vertical rise necessary in order for the appliance to
properly function.
In this example, if H
1
follows:
Referring to Figure 3.6, for a horizontal run of 10 feet, the minimum vertical rise must be 3 ½ feet. Therefore V
+V
+ V
will be need to be a minimum of 3 ½ feet.
2
3
Example 2
elbows or
o
o
elbow off
o
elbows would be 1 horizontal foot each, and the 90
were to be 6 feet, then the total equivalent horizontal length would be calculated as
H
= H
T
= 6 + (2 x 1) + 2
= 10 feet
o
elbow, a horizontal run, and the vent termination. In this
+ H
1
Equivalent
Figure 3.5 Allowable Vent Lengths
o
o
elbow would
1
/10
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