Navien NFC-175 Installation & Operation Manual page 64

When linking multiple water heaters to NFC combi-boiler, only the master unit can provide space heating and slave units must be
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configured for DHW only (You can set only the NFC combi-boiler as the master unit in the cascade system, and the master unit controls the
power on/off status of all the slave units in the system).
Once turned on by the master unit, the water heaters will operate in stages to satisfy the DHW demands.
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After completing the cascade settings and saving the changes, the boiler and water heater units must be turned off then turned back on for
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the changes to take effect.
If errors occur while operating a cascade system, the relevant errors are displayed in the display of the failing unit.
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Power supply to the units must be OFF during the system piping.
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The recommended recirculation flow rate for each water heater is 2-4 GPM. Depending on the number of water heaters and the
Note
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diameter of the recirculation line, it may not be necessary to connect all the NPE "A' series water heaters to the recirculation line.
If this is the case, set any unconnected"A"model water heaters to Internal Recirculation Mode.
For any NPE "A" water heater that is connected to the recirculation line, each individual unit must be set to the proper
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recirculation mode utilizing the 2-way valve and front panel DIP switches. Refer to the NPE Installation Manual for additional
details.
8.1.1 Piping Sizes and Considerations
When plumbing a cascading system, consider the following pipe diameters and flow rates. Note that flow rates above 6.6 ft/s may cause pipe
erosion. These specifications may vary depending on installation conditions.
Piping Sizes for an NFC Boiler with up to 15 NPE Water Heaters
Model
NFC-175/200 NPE-240
1
2
3
4
5
6
7
1 8
9
10
11
12
13
14
15
64 Installing a Cascade System
ΔT=54°F Flow rate (GPM)
14.38
21.57
28.77
35.96
43.15
50.34
57.5
64.72
71.92
79.11
86.30
93.49
100.68
107.87
115.07
Water Velocity (ft/s)
5.61
5.54
5.21
6.53
4.49
5.24
6.00
4.39
4.75
5.34
5.84
6.33
6.79
5.11
5.44
Pipe Diameter (mm/in)
25A 1 in.
30A 1 / in.
1
4
40A 1 / in.
1
2
40A 1 / in.
1
2
50A 2 in.
50A 2 in.
50A 2 in.
65A 2 / in.
1
2
65A 2 / in.
1
2
65A 2 / in.
1
2
65A 2 / in.
1
2
65A 2 / in.
1
2
65A 2 / in.
1
2
80A 3 in.
80A 3 in.