Navien NFC-250/175H Installation Manual page 83
Condensing combi-boilers
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When linking multiple water heaters to NFC-H combi-boiler, only the main unit can provide space heating and
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sub units must be configured for DHW only (You can set only the NFC-H combi-boiler as the main unit in the
cascade system, and the main unit controls the power on/off status of all the sub units in the system).
Once turned on by the main 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
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turned off then turned back on for the changes to take effect.
If errors occur while operating a cascade system, the relevant errors are displayed in the display of the failing
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unit.
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
Note
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number of water heaters and the diameter of the recirculation line, it may not be necessary to
connect all the NPE-A2 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-A2 water heater that is connected to the recirculation line, each individual unit must
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be set to the proper 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-H Boiler with up to 15 NPE-240A2 or NPE-240S2 Water Heaters
Model
NPE-240A2
NFC-H
or
NPE-240S2
1
2
3
4
5
6
7
1
8
9
10
11
12
13
14
15
ΔT=54°F Flow rate
Water Velocity
(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
Pipe Diameter (mm/in)
(ft/s)
5.61
25A
5.54
30A
5.21
40A
6.53
40A
4.49
50A
5.24
50A
6.00
50A
4.39
65A
4.75
65A
5.34
65A
5.84
65A
6.33
65A
6.79
65A
5.11
80A
5.44
80A
1 in.
1
/
in.
1
4
1
/
in.
1
2
1
/
in.
1
2
2 in.
2 in.
2 in.
2
/
in.
1
2
2
/
in.
1
2
2
/
in.
1
2
2
/
in.
1
2
2
/
in.
1
2
2
/
in.
1
2
3 in.
3 in.
Installing a Cascade System
83
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