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Gas Piping Connections
Gas Inlet Adapter
Bottom View
Gas
Regulator
Gas Supply Line
Gas meter's capacity ≥ Total gas capacity of connected appliances
Gas supply
Water Piping Connections
Space Heating System
Pressure Relief
Valve
Space
Space
Heating
Heating
Supply
Return
Install the included 3/4 in, maximum 30
psi pressure relief valve on the space
heating supply.
An ASME approved HV pressure relief
valve for space heating system is
supplied with the boiler.
System Fill Connection
Air Vent Cap
The Navien NCB boilers
have a built-in air vent
on top of the internal
circulator to purge air
from the boiler system.
Before filling the boiler, remove the air vent cap to
allow the system to fill properly. Replace the cap
when the system is full.
Ensure that the Air Vent Cap is removed
Warning
before filling the system.
System will not be properly filled
without the air vent cap removed. Air in
the system may cause malfunctions
and system overheating.
Condensate Drain Connection
A condensate drain pipe must be connected to the 1/2" condensate outlet fitting at
the bottom of the unit and water must be poured into the exhaust connection to fill
the condensate trap.
The boiler is recommended to be the first
appliance to be connected to the gas supply
line.
DHW System
Cold Water
Pressure
Supply
Relief
Valve
DHW
Supply
The DHW pressure relief valve is
not supplied, but is required.
Install an approved 3/4 in,
maximum 150 psi pressure relief
valve on the hot water outlet.
Built-in Water Fill Connection
Navien NCB boiler is equipped with
Note
an auto-feeding water connection
and motorized feeding valve.
Therefore, installation of additional
system water fill connection is not
necessary in most cases.
Syphon
Water
Condensate Outlet
Floor drain
Example:
Gas meter
Boiler
≥
425 CFH
195 CFH
* 1 CFH=1,020 Btuh
• 1/2" rigid pipe can be used; refer to the sizing tables in the Installation &
Operation Manual for limitations. Avoid using 1/2" corrugated connectors
or tubing as noise may occur.
Flow Restrictor (for DHW system)
The boiler has a built-in flow restrictor at
the cold water inlet adapter to limit the
overall DHW flow. Three additional flow
restrictors are provided for different flow
rates.
Flow Restrictors (Orange, Yellow, and Blue)
Refer to the following graph and install
an appropriate restrictor for your DHW
system. See the Installation & Operation
Manual (page 21, 22) for detailed
procedures.
Orange
Yellow
Blue
Flow Rate (GPM) and Water Pressure (psi)
Backflow
Preventer
Make-up
Water
Circulator
Heating
Supply
Make-up
Water
The end of the 1/2" (NPT) plastic piping should drain into a laundry tub or into a floor
drain.
Do not submerge the end of the
Note
pipe in water.
2
+
Furnace
+
Domestic gas stove
58.8 CFH
63.7CFH
Water Piping Connections
Space
Space
Cold
Heating
Heating
DHW
Water
Supply
Return
Supply
Inlet
External Water Fill Connection
Pressure Relief Valve
Air Separator
Expansion Tank
Direct to the
external drain
To the drain via
a neutralizer
To the laundry tub
External drain
via a condensate pump
Built-in
Water Feeder
Connection
Heating
Return
To the laundry
tub
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