Navien NHB-055 Installation & Operation Manual page 26

Expansion Tank
The expansion tank must be sized in accordance with the water
volume of the system as well as the firing rate of the appliance.
It is important to locate the expansion tank, and make-up water
connection, on the inlet side of any pump in the system, as doing
so will guarantee the lowest pressure in the system will be at least
equal to the tank and make-up water pressure.
Ensure the expansion tank cannot become isolated from the
boiler anytime the system is operating. Failure to follow these
instructions may lead to discharge from the pressure relief valve,
which may result in property damage or injury.
The installation of flow checks, motorized valves or
Note
other shutoff devices (other than for the purpose of
servicing) are not permitted between the location of
the "Closely Spaced Tees" and the expansion tank.
Air Handler Interface
The Navien NHB boiler can control the operation of an air
handler when a thermostat is used in combination with the air
handling unit. The Air Handler Interface is designed to stop air
handler operation when the boiler's space heating function is not
operating due to DHW supply demands, boiler errors, or low water
conditions.
The air handler contacts (A/H) turn off when the following
conditions arise:
The PCB DIP SW2 #7 is set to ON.
Thermostat is turned off.
The boiler is supplying DHW, or it is in stand-by mode for DHW
demand.
Level 2 or higher errors occur.
The boiler is turned off.
26 Installing the System Piping
Thermostat Configuration for the Air Handler Interface
Set the PCB DIP SW2 #7 to down position (OFF) to use a thermostat
with the Air Handler.
ON
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Refer to the "3.1.1 Guidelines for a Space Heating Installation" on
page 34 for wiring connections.
WARNING
The boiler, when used in conjunction with an air conditioning
system, must be installed so that the chilled medium is
piped in parallel with the heating boiler. Appropriate valves
must be used to prevent the chilled medium from entering
the boiler.
If the boiler is connected to heating coils located in air
handling units where they can be exposed to refrigerated
air, use flow control valves or other automatic means to
prevent gravity circulation of the boiler water during the
cooling cycle.
ON
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