![background image](http://html2.mh-extra.com/html/navien/nfc-250-175h/nfc-250-175h_installation-manual_3727065041.webp)
41
Installing the System Piping
3.6.7 System Application - Combi Pre-Heat Mode
Combi pre-heat allows NFC-H boilers to pre-heat to ensure a quick supply of hot water when there is no external
recirculation system. This mode is enabled by default. (Refer to the combi pre-heat section in “11.5.3 Setting the
DHW Operation” on page 114 for details.)
3.6.8 System Application - External Recirculation with NaviCirc
The following pump models are recommended for use with the NFC-H boiler and DHW recirculation systems.
When using the indicated pump models, observe the following maximum recirculation pipe lengths:
●
100 feet (30 m) equivalent length of
1
/
2
” copper pipe
●
400 feet (120 m) equivalent length of
3
/
4
” copper pipe
External Recirculation Mode
For best performance, select the Intelligent or Weekly option in the External recirculation DHW recirculation
menu. To use the aquastat mode, install an aquastat to the DHW pipe lline and connect to the CNC6 terminal on
the PCB. (Refer to “3.7.4 Wiring Diagram - Zone Pump System with DHW Recirculation” on page 48 for details.)
Note
Combi pre-heat is the default mode for DHW recirculation. To select external recirculation, refer to the
combi pre-heat and external recirculation sections in "11.5.3 Setting the DHW Operation" on page
114 for details.
N
A/H
DHW
PRI
L
N
L
N
L
N
L
N
L
Z3
Z2
Z1
N
A/H
DHW
PRI
L
N
L
N
L
N
L
N
L
Z3
Z2
Z1
SUPPLY
TEMPERATURE SENSOR
RETURN
OUTDOOR
T/S_ZONE3
R
W
C
T/S_ZONE2
R
W
C
T/S_ZONE1
R
W
C
AC24VN
AC24VL
lLWCO
R
W
C
T/S_Recir
COM
NO
NC
ZONE
_V/V3
COM
NO
NC
ZONE
_V/V2
COM
NO
NC
ZONE
_V/V1
* Recirculation
Pump
NaviCirc
(Sold Separately)
DHW Supply
Pump Ground
Return Water
City Water Supply
Check Valve
Recirculation
Pump
(max. 2.5 A)
* A Taco 008-BC6 or Grundfos 15-42 BUC7 (or equivalent) circulation pump is recommended for use with the NFC-H boiler and
DHW recirculation systems.
* When using the external recirculation mode, observe the following maximum recirculation pipe lengths including fittings (
3
/
4
”
pipe is recommended). Lengths in excess of these limits will require a larger recirculation pump.
Maximum Pipe Lengths
Pipe Diameter
1
/
2
"
3
/
4
"
Maximum Pipe Length
100 ft (30 m)
400 ft (120 m)
Note
●
Install the NaviCirc recirculation valve on the faucet furthest from the NFC-H boiler.
●
If installed in close proximity to the boiler, faucets further down the supply line will take longer to
receive hot water.
Summary of Contents for NFC-250/175H
Page 67: ...67 Venting for Combustion Air WARNING The vent installation detector Detectable Undetectable...
Page 149: ...Memo...
Page 150: ......