Navien NHB-055 Installation & Operation Manual page 19

Pressure Relief Valve
To complete the space heating system installation, you must install
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a / in, 30 psi (max.) pressure relief valve on the space heating hot
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water outlet. An ASME approved HV pressure relief valve for space
heating system is supplied with the boiler.
WARNING
Installing the pressure relief valve improperly may result
in property damage, personal injury, or death. Follow all
instructions and guidelines when installing the pressure
relief valve. The valve should be installed only by a licensed
professional.
The pressure relief valve must be installed at the boiler
outlet and in the vertical position, as shown in this section,
with the drain pipe outlet exiting the side of the pressure
relief valve horizontally and elbowing down.
CAUTION
Install the pressure relief valve as close to the boiler as possible.
No other valve should be installed between the pressure relief
valve and boiler.
When installing the pressure relief valve, follow these guidelines:
Ensure that the valve's discharge capacity is equal to or greater
than the maximum pressure rating of the boiler's space heating
system.
Ensure that the maximum BTU/H rating on the pressure relief
valve is equal to or greater than the maximum input BTU/H
rating of the boiler.
Direct the discharge piping of the pressure relief valve so that
hot water does not splash on the operator or equipment.
Attach the discharge line to the pressure relief valve and install
the end of the line within 6-12 in (150-300 mm) above the floor.
Ensure that the discharge line provides complete and
unobstructed drainage. Do not install a reducing coupling or
other restrictions on the discharge line.
If the relief valve discharges periodically, this may be caused by
thermal expansion when the expansion tank is full or undersized.
Do not plug the relief valve.
There are two pressure relief valve installation methods. In Method
1, the pressure relief valve is installed on top of the boiler and in
Method 2 it is installed in a manifold system.
If the installed system does not have a Navien manifold system,
install a pressure relief valve with the air vent. The illustration
below shows an example of a pressure relief valve installed with
the air vent.
Air Vent
External LWCO
Method 1.
Refer to the following illustration for a pressure relief valve
installation in the space heating system. A Watts M330-M1 pressure
relief valve ( 3 / in, HV, Max 30 psi) is provided with the boiler.
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Method 2.
Pressure
Relief Valve
Pressure Relief
Valve
Installing the System Piping 19