76
Installing a Common Vent System
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.
H
W
D
Intake
Exhaust
Note
Ɣ
Every 90° elbow used is equivalent to 8 linear feet
(2.4 m) of vent length.
Ɣ
The pipe branch that connects the individual
appliance to the common vent trunk must be
within 20 equivalent feet.
Common Vent Length Table [Total Length (L) =
W + H]
Vent Length for NFB Boiler Units
Required
Load
(Total BTU/h)
Model
Total Length (ft)
NFB-301C
D=4”
D=6”
D=8”
602,000
2
71
160
903,000
3
42
96
150
1,204,000
4
35
80
142
Required
Load
(Total BTU/h)
Model
Total Length (ft)
NFB-399C
D=4”
D=6”
D=8”
798,000
2
53
120
1,197,000
3
35
80
142
1,596,000
4
26
60
106
Summary of Contents for NHB Series
Page 120: ...120 Appendixes 12 6 Component Assembly Diagrams and Part Lists 12 6 1 Case Assembly NFB 301C...
Page 122: ...122 Appendixes 12 6 2 Case Assembly NFB 399C...
Page 124: ...124 Appendixes 12 6 3 Heat Exchanger and Waterway Assembly NFB 301C...
Page 126: ...126 Appendixes 12 6 4 Heat Exchanger and Waterway Assembly NFB 399C...
Page 128: ...128 Appendixes 12 6 5 Combustion Parts Assembly NFB 301C...
Page 131: ...131 Appendixes 12 6 6 Combustion Parts Assembly NFB 399C...
Page 134: ...Memo...
