86 Installing a Common Vent System
Common Vent Length Table
[Total Length (L) = W + H]
Vent Lengths for an NCB-H Boiler with up to
7 NPE Water Heaters
The following table provides information on the
required load amount and the total length for
one NCB-H boiler with up to 7 NPE water heaters
installed.
Required
Load
(Total
BTU/H)
Model
Total Length (ft)
NCB-
250/150H
NPE-240 D=3” D=4” D=6” D=8”
409,900
1
1
60
106 200
609,800
2
40
71
160
809,700
3
30
53
120
1,009,600
4
96
150
1,209,500
5
80
142
1,409,400
6
68
121
1,609,300
7
60
106
Note
Every 90° elbow used is equivalent to 8
linear feet (2.4 m) of vent length.
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
D
W
H
Intake
Siphon loop
Drain hose
End cap
Drain
Summary of Contents for NCB-190/060H
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