Navien NHB-055 Installation & Operation Manual page 61

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
Common Vent Length Table [Total Length (L) =
W + H]
Vent Length for NHB Boiler Units
Model
Required Load
(Total BTU/H)
NHB-110/150
300,000 2
450,000 3
600,000 4
750,000 5
900,000 6
1,050,000 7
1,200,000 8
Every 90° elbow used is equivalent to 8 linear feet (2.4
Note
m) of vent length.
Exhaust
D
Intake
Total Length (ft)
D=3" D=4" D=6" D=8"
60 106 200
40 71 160
30 53 120
24 42 96 150
35 80 142
30 68 121
26 60 106
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 NHB boiler units.
The illustration is intended for reference purposes
Note
only.
Installing a Common Vent System 61