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81
Installing a Common Vent System
Note
●
Every 90° elbow used is equivalent to
8 linear feet (2.4 m) of vent length.
●
Branch pipe lengths are not added
to the allowable equivable vent
lengths that are provided in the
following charts.
Example of a Typical Installation
(Direct Vent Only)
The following illustration depicts an example of a
common vent system installed for a cascade system
of 8 Navien NFB-H boiler units.
Note
The illustration is intended for
reference purposes only.
9.1.2 Determining the Length of a
Common Vent System
Follow the instructions listed below to determine
the length of a common vent.
1. Add the BTU/H input ratings for each unit in the
cascading system to determine the total BTU/H
rating.
2. Determine the total length (L) of the common
vent, which consists of the horizontal width (W)
and the vertical height (H): Total length (L) = W
+ H.
Exhaust
W
H
D
Intake
Siphon loop
Drain hose
End cap
Drain
Common Vent Length Table [Total
Length (L) = W + H]
Vent Length for NFB-H Boiler Units
Required Load
(Total BTU/H)
Model
Total Length (ft)
NFB-
175H/200H D=3” D=4” D=6” D=8”
399,800
2
60 106 200
599,700
3
40
71 160
799,600
4
30
53 120
999,500
5
96 150
1,199,400
6
80 142
1,393,300
7
68 121
1,599,200
8
60 106
Summary of Contents for NFB-175H
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