Navien NHB H Series User manual

WARNING
If the information in these instructions is not followed exactly, a fire or explosion may result,
causing property damage, personal injury, or death.
Do not store or use gasoline or other flammable vapors and liquids in the vicinity of this
or any other appliance.
WHAT TO DO IF YOU SMELL GAS
●Do not try to light any appliance.
●Do not touch any electrical switch; do not use any phone in your building.
●Immediately call your gas supplier from a neighbor’s phone. Follow the gas supplier’s
instructions.
●If you cannot reach your gas supplier, call the fire department.
Installation and service must be performed by a qualified installer, service agency or the
gas supplier.
The installation must conform with local codes or, in the absence of local codes, the National Fuel
Gas Code, ANSI Z223.1/NFPA 54 and/or CSA B149.1, Natural Gas and Propane Installation Code.
ALWAYS read and follow this manual
completely before using the boiler.
Save for future reference.
Installation and Operation Manual
NHB-H Condensing Boilers
Model NHB-055H
NHB-080H
NHB-110H
NHB-150H

2Contents
9. Installing a Common Vent System 77
9.1 About the Common Vent System 77
9.2 Navien Common Vent Collar Kit (Back-
draft Damper) 82
9.3 Starting the Common Vent System 83
9.4 Connecting and Terminating the Vent
Pipe 87
9.5 Setting up the Common Vent System 90
9.6 Common Vent Termination Clearances 90
9.7 Installing a Condensate Drain 92
9.8 Maintenance 93
10. Installation Checklist 94
11. Operating the Boiler 97
11.1 Operating the Boiler for the First Time 97
11.2 Turning the Boiler On or Off 98
11.3 Start-Up Wizard 99
11.4 Adjusting the System Temperatures 100
11.5 Resetting the Boiler 103
11.6 Accessing Basic Menu Items 103
11.7 Viewing Basic Information 103
11.8 Setting the Space Heating Operation 104
11.9 Setting the DHW Operation (Indirect) 107
11.10 Viewing Error History 108
11.11 Viewing Other System Information 108
11.12 Setting the Display Options 109
11.13 Accessing Advanced Menu Items 109
11.14 Understanding Error Codes 119
12. Appendixes 120
12.1 Gas & High Altitude Conversion 120
12.2 Wiring Diagram 128
12.3 Ladder Diagram 129
12.4 Outdoor Temperature Sensor 130
12.5 Outdoor Reset Control 130
12.6 Component Assembly Diagrams and
Parts Lists 132
12.7 Requirements for the State of
Massachusetts 139
13. LIMITED WARRANTY NAVIEN, INC. 140
Important Safety Information 3
1. About the Boiler 5
1.1 Included Items 5
1.2 Accessories 5
1.3 Specifications 6
1.4 Components 8
1.5 Dimensions 10
1.6 Rating Plate 11
2. Installing the Boiler 12
2.1 Choosing an Installation Location 12
2.2 Mounting the Boiler to the Wall 14
3. Installing the System Piping 16
3.1 Installing a Space Heating System 16
3.2 Connecting the Condensate Drain 23
3.3 Filling the System 26
3.4 Testing the Water System 26
3.5 Considerations for System Applications 27
3.6 Examples of Electrical Connections 34
4. Connecting the Gas Supply 46
4.1 Gas Pipe Sizing Tables 49
4.2 Measuring the Inlet Gas Pressure 50
5. Venting for Combustion Air 52
5.1 Venting the Boiler 53
5.2 About the Vent Installation Detector 55
5.3 Selecting a Vent Type 57
5.4 Selecting Vent Pipe Materials 61
5.5 Measuring Vent Length 62
5.6 Terminating the Vent 63
6. Setting the DIP Switches 67
6.1 DIP Switch 1 (Set of 6 Switches) 67
6.2 Dip Switch 2 (Set of 8 Switches) 68
7. Connecting the Power Supply 70
8. Installing a Cascade System 72
8.1 Connecting Water Supplies 72
8.2 Connecting the Communication Cables 76
Contents

3Important Safety Information
The following Safety Alert Symbols are used
in this manual. They are used to alert you
to potential personal injury hazards. Obey
all safety messages that follow this symbol to avoid
possible serious injury or death. This Safety Alert
Symbol precedes any safety message about risk of
personal injury. It may also be accompanied by one
of the following signal words.
If the information in these instructions is not
followed exactly, a fire or explosion may result,
causing property damage, personal injury or death.
DANGER
Indicates a hazardous situation that if not
avoided will result in death or serious injury.
WARNING
Indicates a hazardous situation that if not
avoided could result in death or serious injury.
CAUTION
Indicates a potentially hazardous situation that
if not avoided could result in minor or moderate
injury.
NOTICE
Indicates information considered important but
not hazard-related (such as property damage).
DANGER
If you smell gas:
●Do not try to light any appliance.
●Do not touch any electrical switches or use
landline phones.
●From a neighbor’s phone, call your gas
provider and follow their instructions.
●If you cannot reach your gas provider, call the
fire department.
●Do not return to your home until authorized
by your gas supplier or the fire department.
Do not use or store flammable products,
such as gasoline, solvents, or adhesives in
the same room or area as the boiler.
●The boiler has a main burner flame that can
turn on at any time and can ignite flammable
vapors. Vapors from flammable liquids can
explode and catch fire, causing death or
severe burns.
●Vapors cannot be seen and are heavier than
air. They can travel long distances along the
ground and can be carried from other rooms
to the boiler’s main burner flame by air
current.
●Keep all flammable products far away from
the boiler and store them in approved
containers. Keep the containers closed tightly
and out of the reach of children and pets.
Important Safety Information
Product Installation Information
Model
Date Purchased
Gas Type
Serial Number

4Important Safety Information
California law requires the following Prop 65
warning to be provided:
WARNING
Cancer and Reproductive Harm -
www.P65Warnings.ca.gov.
WARNING
To prevent death, serious injury, or property
damage:
●Do not turn on the boiler unless the water
and gas supplies are fully opened.
Doing so may damage the boiler.
●Do not use this boiler for anything other
than its intended purpose, as described in
this manual.
●Do not remove the front cover unless
the power to the boiler is turned off or
disconnected.
Failure to do so may result in electric shock.
●When servicing the controls, label all wires
prior to disconnecting them.
Failure to do so may result in wiring errors,
which can lead to improper or dangerous
operation. Verify proper operation after
servicing.
●Do not use unapproved replacement or
accessory parts.
Doing so may result in improper or dangerous
operation and will void the manufacturer’s
warranty.
●Do not place anything in or around the
vent terminals, such as a clothes line, that
could obstruct the air flow in or out of the
boiler.
●This boiler has been approved for use in
the USA and Canada only.
Using the boiler in any other country will void
the manufacturer’s warranty.
WARNING
To prevent death, serious injury, or property
damage:
●Do not store or use gasoline or other
flammable liquids near this boiler.
Doing so may result in fire or explosion.
●Do not place combustibles, such as
newspapers or laundry, near the boiler or
venting system.
Doing so may result in a fire.
●Do not place or use hair sprays, spray
paints, or any other compressed gasesnear
the boiler or venting system, including the
vent termination.
Doing so may result in fire or explosion.
●Do not operate the boiler with the front
cover opened.
Doing so may result in fire or carbon
monoxide (CO) poisoning, which may result
in property damage, personal injury, or death.
●Do not operate this boiler without proper
venting.
Doing so may result in fire or carbon
monoxide (CO) poisoning, which may result
in property damage, personal injury, or death.
●Do not touch the power cord or internal
components of the boiler with wet hands.
Doing so may result in electric shock.

5About the Boiler
1.1 Included Items
When you open the box, you will find the following
items with the boiler. Check the box for each of the
following items before installing the boiler.
Installation &
Operation Manual,
User’s Information Manual
Quick Installation Manual
2 in Vent Termination Caps
(x2)
2 in Wall Flanges
(x4)
Spare Parts Air Vent
Wall Mounting Bracket Tapping Screws & Anchors
(x4)
Pressure Relief Valve,
Heating Conversion Kit
Outdoor Temperature
Sensor and Cable
Air Vent Bushing
(3/4in to 1/2in)
1.2 Accessories
The following optional accessories are available for
the boiler.
Navien Manifold System
(for primary zone)
Navien Manifold System
(for secondary zone)
STS Manifold System
(for primary zone)
Condensate Neutralizer
Kit
Zone Controller
(FMZ-20/30)
Zone Controller
(FMZ-40/60)
System Supply/Return
Temperature Sensors
Navi-Link
(Wi-Fi Control System)
COM
WI-FI
Ready-Link Rack NaviLink Lite
NaviClean Valve Kit
Universal Adapter Kit
1. About the Boiler

6About the Boiler
1.3 Specifications
The following tables list the specifications for the boiler. Additional specifications for water, gas, electricity, and
vent connections are provided in the Installation section.
Space Heating Specifications
Navien Condensing Boiler
Space Heating Ratings Other Specifications
Model
Number
1
Heating Input (MBH) Heating
Capacity
2
(MBH)
Net AHRI
Rating Water
3
(MBH)
AFUE
2
(%) Water
Pressure
Water
Connection Size
(Supply, Return)
Min Max
NHB-055H 855 51 44 95
12–30 psi 1 in NPT
NHB-080H 880 73 64 95
NHB-110H 10 110 101 88 95
NHB-150H 10 150 136 118 95
Note 1. Ratings are the same for natural gas models converted to propane use.
2. Based on U.S. Department of Energy (DOE) test procedures.
3. The net AHRI water ratings shown are based on a piping and pickup allowance of 1.15. Consult
Navien before selecting a boiler for installations having unusual piping and pickup requirements,
such as intermittent system operation, extensive piping system, etc.

7About the Boiler
General Specifications
Item NHB-055H NHB-080H NHB-110H NHB-150H
Dimensions 17.3 in (W) x 12.8 in (D) x 23.8 in (H)
Weight 73 lb (33 kg) 80 lb (36 kg)
Installation Type Indoor Wall-Hung
Venting Type Forced Draft Direct Vent
Ignition Electronic Ignition
Natural Gas Supply Pressure (from
source) 3.5 in–10.5 in WC
Propane Gas Supply Pressure (from
source) 8.0 in–13.5 in WC
Natural Gas Manifold Pressure -0.11 in WC -0.17 in WC -0.26 in WC -0.40 in WC
Propane Gas Manifold Pressure -0.11 in WC -0.17 in WC -0.25 in WC -0.41 in WC
Gas Connection Size 3/4 in NPT
Power Supply
Main Supply 120V AC, 60Hz
Maximum Power
Consumption Less than 15 amperes
Materials Casing Cold-rolled carbon steel
Heat Exchangers Primary and Secondary Heat Exchangers: Stainless Steel
Venting
Exhaust 2 in or 3 in PVC, CPVC, approved polypropylene*
2 in or 3 in Special Gas Vent Type BH (Class III, A/B/C), Stainless Steel
Intake 2 in or 3 in PVC, CPVC, polypropylene
2 in or 3 in Special Gas Vent Type BH (Class III, A/B/C), Stainless Steel
Vent Clearance 0 in to combustibles
Safety Devices
Flame Rod, APS, Ignition Operation Detector
Water Temperature High Limit Switch, Exhaust Temperature High
Limit Sensor, Water Pressure Sensor, Vent Installation Detector (VID)
* For more information about the approved vent materials, refer to“5.4 Selecting Vent Pipe Materials” on page 61.
Temperature Setting Range
Item Temperature Setting Range Remarks
Space
Heating
Supply 77–185°F (25-85°C) Actual supply and return temperatures
vary depending on the selected outdoor
reset curve.
Return 68–158°F (20-70°C)
Note For more information about the space heating temperature setting range, refer to“11.8 Setting the
Space Heating Operation”on page 104.

8About the Boiler
1.4 Components
The following diagram shows the key components of the boiler. Component assembly diagrams and particular
parts lists are included in the Appendixes.
Intake Air
Pressure Sensor
(LWCO)
Power Switch
Air Vent Connection
Vent Installation
Detector (VID)
Exhaust Duct
Flue Duct
Front Panel
PCB
Air Filter

9About the Boiler
Dual Venturi
Ignition Transformer
Igniter &
Flame Rod
Primary Heat
Exchanger
Secondary Heat
Exchanger
Gas Valve
Air Pressure Sensor
(APS)
Gas Connection
Space Heating Supply
Fitting
Condensate Trap
Space Heating
Return Fitting
Fan & Motor
Metal Fiber
Premix Burner
Mixing
Gas Guide

10 About the Boiler
1.5 Dimensions
The following diagrams show the dimensions of the boiler and the table lists the supply connections.
23.6" (600 mm)
Supply Connections
Description Diameter
AAir Intake 2 in
BExhaust Gas Vent 2 in
CAir Vent Connection
3
/
4
in
DRubber Grommet 1 in
ESpace Heating Return 1 in
FCondensate Outlet
1
/
2
in
GGas Connection
3
/
4
in
HSpace Heating Supply 1 in
Overhead View
AB C
15”(400 mm)
2.3”(60 mm)
6.5”(165 mm)
2.6” (67mm)
17”(440 mm)
2.5”(66 mm)
Supply Connections
DFE H
G
9.8”(249 mm) 6”(152 mm)
12.2”(311 mm)*
2.3”(60 mm)
5.7”(145 mm)

11About the Boiler
1.6 Rating Plate
The Navien NHB-H boilers come from the factory configured for use with Natural Gas (NG). Before starting
the installation, check the rating plate located on the side of the boiler to ensure that the boiler matches the
gas type, gas pressure, water pressure, and electrical supply available in the installation location. If the boiler
does not match each of these ratings, do not install the boiler. If conversion to Propane Gas is required, the
included gas conversion kit must be used. Refer to“12.1 Gas & High Altitude Conversion”on page 120 for details.
Note The Propane Gas & High Altitude Conversion Kit is attached to the interior of the boiler cabinet. You
will need to remove the front cover to access the Propane Gas & High Altitude Conversion Kit. If you
need assistance, please call a licensed professional or Navien Technical Support at 1-800-519-8794.
WARNING
To prevent death, serious injury or property damage:
Before starting the installation, check the Rating Plate located on the side of the boiler to ensure that the
boiler matches the gas type, gas pressure, water pressure, and electrical supply available in the installation
location.
If the boiler does not match each of these ratings, do not install the boiler. Using a different gas type will
result in abnormal combustion and malfunction of the boiler.
●ONLY a licensed professional should connect the gas supply.
●ALWAYS leak test the appliance and the gas connections before operating the appliance.
●This boiler cannot be converted from natural gas to propane without a Navien Propane Gas & High Altitude
Conversion Kit. NEVER attempt a field conversion of this boiler without using the Navien Propane Gas &
High Altitude Conversion Kit. Doing so will result in dangerous operating conditions and will void the
warranty.
Navien Inc. is not liable for any property damage, personal injury or death resulting from improper
conversions.
This appliance complies with the requirements of SCAQMD Rule 1146.2 for NOx emissions of 14 ng/J or 20 ppm
at 3% O
2
.

12 Installing the Boiler
2.1 Choosing an Installation
Location
When choosing an installation location, you
must ensure that the location provides adequate
clearance for the boiler, adequate venting and
drainage options, and sufficient access to gas,
water, and electrical supplies. Carefully consider
the following factors when choosing an installation
location:
WARNING
●Do not install outdoors. Outdoor installation
may result in property damage, severe
personal injury, or death. Damage to the
boiler resulting from installation outdoors is
not covered by warranty.
●Do not install this boiler in a recreational
vehicle, trailer, boat or other moving vehicles
as it will result in a Carbon Monoxide
Poisoning Hazard.
Note If the boiler is installed in Massachusetts,
refer to “Requirements for the State of
Massachusetts”on page 139.
Compliance Requirements
●Local, state, provincial, and national codes, laws,
regulations, and ordinances.
●National Fuel Gas Code, ANSI Z223.1-latest
edition.
●Standard for Controls and Safety Devices for
Automatically Fired Boilers, ANSI/ASME CSD-1,
when required.
●National Electrical Code.
●For Canada only: B149.1 Installation Code,
CSA C22.1 Canadian Electrical Code Part 1,
CSA-B214-12 Installation code for hydronic
heating systems, and any local codes.
Access to Utilities
●Water – the installation location should be near
where the domestic water supply enters the
building.
●Gas – the installation location should be near
where the gas supply enters the building.
●Electricity – the installation location should
be near where the electrical supply enters the
building.
Humidity and Contact with Water
When installing the boiler, avoid places with
excessive humidity. The boiler has electric gas
ignition components. Moisture can get inside
the boiler and damage the ignition system. The
boiler must be installed in a way to ensure that
the gas ignition system components are protected
from water (dripping, spraying, rain, etc.) during
operation and service.
Adequate Drainage
The boiler produces a significant amount of
condensate during operation. The boiler should be
located near a suitable drain and where damage
from a possible leak will be minimal. Installing the
boiler in a location without a drain will void the
warranty and Navien will not be responsible for
water damages that occur as a result. For more
information about condensate drainage, refer to“3.2
Connecting the Condensate Drain”on page 23.
The boiler must be located in an area where leakage
of the unit or connections will not result in damage
to the area adjacent to the appliance or to lower
floors of the structure. When such locations cannot
be found, installation of an adequately drained drain
pan under the boiler is highly recommended. When
installing the drain pan, ensure that the installation
does not restrict combustion air flow.
2. Installing the Boiler

13Installing the Boiler
Adequate Installation Clearances
NOTICE
Do not install the boiler on carpeting.
Install the boiler in an area that allows for service
and maintenance access to utility connections,
piping, filters, and traps. Based on the installation
location, ensure that the following clearances are
maintained:
Top
Back
Side
Bottom
Front
Side
Clearance from: Indoor Installation
Top 9 in (229 mm) minimum
Back 0.5 in (13 mm) minimum
Front 4 in (100 mm) minimum
Sides 3 in (76 mm) minimum
Bottom 12 in (300 mm) minimum
Adequate Venting and Ventilation
Select a location that requires minimal venting.
Consider venting restrictions caused by windows,
doors, air intakes, gas meters, foliage, and other
buildings. For more information about venting, refer
to“5. Venting for Combustion Air” on page 52.
To ensure adequate venting and ventilation, follow
these guidelines:
●Maintain proper clearances from any openings in
the building.
●Ensure that the vent termination is at least 12 in
(300 mm) above ground, 12 in (300 mm) above
the highest anticipated snow level, or as required
by local codes, whichever is greater.
●Do not enclose the vent termination.
●Install the exhaust vent in an area that is free
from any obstructions, where the exhaust will not
accumulate.
●Avoid Installations of the boiler where moisture
from the exhaust may discolor or damage walls.
●Do not install the boiler in bathrooms, bedrooms,
or any other occupied rooms that are normally
kept closed or not adequately ventilated.
●Install a carbon monoxide detector in the
dwelling area nearby the appliance. Refer
to manufacturer’s instructions as well as the
Consumer Product Safety Commission (CPSC)
and Environmental Protection Agency (EPA)
recommendations for proper use of carbon
monoxide alarms.

14 Installing the Boiler
2.2 Mounting the Boiler to the
Wall
Navien NHB-H boilers come with an upper
mounting bracket that is pre-drilled at 16 in
(400 mm) on center for easy installation on standard
wall studs. If the strength of the wall is insufficient
or if the framing is non-standard or uneven,
reinforce the area before installing the boiler. Avoid
installation on common walls as the unit will make
some operational noises while it is running.
To mount the boiler to the wall:
1. Affix the bracket securely to the wall and ensure
that it is level and that it can support the weight
of the boiler.
2. Align the grooves on the back of the boiler with
the tongues on the mounting bracket and hang
the boiler on the bracket.
When mounted with the mounting bracket, the
boiler will have a 5/8 in (16 mm) clearance from
the back of the wall.
CAUTION
It is necessary to leave clearance for service
access.
Clean, Debris and Chemical-free
Combustion Air
●Do not install the boiler in areas where dust and
debris may accumulate or where hair sprays,
spray detergents, chlorine, or similar chemicals
are used.
●Do not install the boiler in areas where gasoline or
other flammables are used or stored.
●Ensure that combustible materials are stored
away from the boiler and that hanging laundry or
similar items do not obstruct access to the boiler
or its venting.
Operating Temperature
The ambient temperature at the installation location
must be above 32˚F (0˚C) and below 120˚F (49˚C).
High Elevation Installations
This unit may be installed at elevations up to 10,100
ft (3,078 m) for use with natural gas and propane.
Refer to“6. Setting the DIP Switches”on page 67
for the appropriate altitude setting.
WARNING
●ALWAYS read and follow the Natural Gas High
Altitude Conversion Guide when installing
the gas orifice included with the kit in order
to prevent death, serious injury or property
damage.
●The front cover will need to be removed
from the boiler to access the High Altitude
Conversion Kit.
●Do NOT install this boiler at elevations above
10,100 ft (3,078 m).

15Installing the Boiler
WARNING
●The boiler is heavy. Always lift the unit with
assistance. Be careful not to drop the boiler
while lifting or handling it to avoid bodily
injury or damage to the unit.
●Install the boiler in the upright, vertical
position. Installation in any other orientation
will result in improper boiler operation and
property damage, and could result in serious
personal injury or death.
NOTICE
●Ensure that the structure of the installation
location is sturdy enough to support the full
weight of the installed boiler, including the
water contained in the heat exchanger and
related piping.
●The wall must be vertical, and it must be
capable of carrying the weight of the boiler.
●Do not mount the boiler to drywall that has
not been reinforced.
●Do not rest the boiler on the bottom end
after removing it from the shipping carton.
Doing so may result in excessive pressure on
protruding pipes and resulting in product
damage. If you must put the boiler down, lay
it on its back or put it inside the protective
shipping base.
3. Install two set screws through the bracket at the
bottom of the boiler to secure the boiler on the
wall.

16 Installing the System Piping
Prior to connecting piping to the boiler, flush the
entire system to ensure it is free of sediment, flux,
solder, scale, debris or other impurities that may
be harmful to the system and boiler. During the
assembly of the heating system, it is important
to keep the inside of the piping free of any debris
including construction dust, copper burr, sand and
dirt.
For retrofits, all system piping including radiators,
must be cleaned of all build-up including sludge
and scale. All systems, old and new, must be
cleaned to remove flux, grease and carbon residue.
Navien recommends cleaning the boiler system
with cleaning products specially formulated
for boiler systems. For retrofit applications with
heavy limescale and sludge deposits, a heavier
duty cleaner may be required. For information on
performing the cleaning, follow the instructions
included with the boiler system cleaner products.
NOTICE
●Failure to rid the heating system of the
contaminants listed above will void your
warranty and may result in premature heat
exchanger failure and property damage.
●To avoid damaging the connectors on the
boiler, use two wrenches when tightening
piping to the boiler. Use one wrench to
prevent the connector at the boiler from
turning, and use the other wrench to tighten
the connection. Damaged connectors may
result in system leaks.
●Properly support the piping with hangers. Do
not allow the piping to be supported by the
boiler or its accessories.
3.1 Installing a Space Heating
System
The primary and secondary heat exchangers of the
Navien NHB-H boilers are designed to attain the
highest level of heat transfer in a compact design.
To accomplish this, the heating water flows through
a series of tubes (secondary heat exchanger) and
finned tubes (primary heat exchanger), designed
to maximize the heat transfer area. To maintain
the efficient and reliable operation of the heat
exchangers, and to avoid heat exchanger failure, it
is critical to ensure the rules and guidelines in this
section are followed.
WARNING
Failure to follow the instructions provided in this
section will void the warranty and may result in
property damage, fire, serious injury or death.
3.1.1 Guidelines for a Space Heating
Installation
Read and follow the guidelines listed below to
ensure safe and proper installation of a boiler
heating system.
Freeze Protection for a Space Heating
System
●Freeze protection products may be used for the
space heating system. Freeze protection for new
or existing systems requires specially formulated
glycol, which contains inhibitors to prevent
the glycol from attacking the metallic system
components.
●Before using freeze protection products,
ensure that system fluid contains proper
glycol concentration and the inhibitor level
is appropriate. Navien recommends against
exceeding a 35% concentration of glycol.
●When using the freeze protection products, the
system must be tested at least once a year, and as
recommended by the manufacturer of the glycol
solution.
●When using the freeze protection products,
allowance should be made for expansion of the
glycol solution.
●Freeze damage is not covered by the warranty.
●The use of glycol results in a greater head loss due
to its higher viscosity compared to water.
3. Installing the System Piping

17Installing the System Piping
3.1.2 Essential Elements in a Space
Heating System
Air Vent
The Navien NHB-H boiler comes with an air vent and
an adapter bushing that must be connected to the
air vent connection. The vent efficiently removes the
air from the boiler. The following figure illustrates an
example of a typical air vent installation.
Supply
Air Vent
Bushing
Air Vent
Return
Also, an external LWCO and a pressure relief valve
can be installed at the air vent connection. Refer to
“Low Water Cut Off (LWCO) Device” on page 17
and“Pressure Relief Valve”on page 18.
Note Before installing the vent line and any
vent fittings, you must be familiar with
the LWCO and pressure relief valve
installation guidelines.
Low Water Cut Off (LWCO) Device
Internal LWCO
The Navien NHB-H boiler is equipped with a factory-
installed, pressure-sensing type low water cutoff
(LWCO) device. The minimum operation pressure for
this device is 6 psi by default.
Note
When the built-in water pressure sensor
detects insufficient water level in the
boiler, error code E302 is displayed on the
front panel requiring a manual boiler reset.
Refer to local codes to determine if a LWCO device is
required for your system and ensure that the built-in
device meets the requirements.
NOTICE
For systems requiring freeze protection, use only
inhibited propylene glycol, specially formulated
for hydronic heating systems; use of other types
of antifreeze may be harmful to the system and
will void the warranty.
System Pressure
●The Navien NHB-H boiler is intended solely for
use in pressurized closed loop heating systems
operating with 12-30 psi water pressure at the
boiler outlet. To obtain the minimum system
design pressure, follow the piping diagrams
illustrated in this section.
●The Navien NHB-H boiler’s space heating system
is not approved for operation in an“open system”,
thus it cannot be used for direct potable water
heating or to process heating of any kind.
Oxygen Elimination
This boiler may only be installed in a pressurized
closed-loop heating system, free of air (oxygen)
and other impurities. All of the air should be
removed from the system during commissioning
via strategically placed and adequately sized air
removal appliances, located throughout the heating
system.
Note See the examples of system application
at the end of this section detailing
the installation location of the air
removal device, in case an additional air
removal device is required for a specific
application.
NOTICE
●Immediately repair any leaks in the system
piping to avoid adding make-up water. Make-
up water adds oxygen and minerals to the
system that may lead to heat exchanger failure.
●Do not solder piping directly onto the water
connections, as the heat may cause damage
to internal components. Use threaded water
connections only.
●Failure to follow these instructions may result in
poor performance, unnecessary wear of system
components and premature failure.

18 Installing the System Piping
Backflow Preventer
Install a backflow preventer valve in the make-up
water supply to the unit as required by local codes.
Expansion Tank
An expansion tank must be installed in the space
heating piping to prevent excessive pressure
from building in the system. See the examples of
system application at the end of this section for the
installation location. Refer to the expansion tank
manufacturer’s instructions for additional details.
Follow the guidelines below when installing an
expansion tank.
●Connect an air separator to the expansion tank
only if the air separator is located on the suction
side of the system pump.
●Install the make-up water connection at the same
location as the expansion tank’s connection to
the system.
●When replacing an expansion tank, consult the
expansion tank manufacturer’s literature for
proper sizing.
●For diaphragm expansion tanks, always install
an automatic air vent on the top side of the air
separator to remove residual air from the system.
Isolation Valves and Unions
●Full port ball valves are required for the boiler
system. Failure to use full port ball valves could
result in a restricted flow rate through the boiler.
●Check valves are recommended for installation.
Failure to install check valves could result in a
reverse flow condition during pump(s) off cycle.
●Unions are recommended for unit serviceability.
Pressure Relief Valve
To complete the space heating system installation,
you must install a
3
/
4
in, 30 to 80 psi (max.) pressure
relief valve on the space heating hot water outlet.
An ASME approved Watts 174A pressure relief valve
(
3
/
4
in, HV, Max 30 psi) is provided with the boiler.
External LWCO
If local codes require a separate LWCO device,
install one separately. Combining the LWCO with
the air vent simplifies the installation. The following
illustration shows an example of a separately
installed external LWCO.
6" (152 mm) min.
External
LWCO
The external LWCO must be installed at least 6 in
(152 mm) above the top of the heat exchanger.
Refer to“3.6.2 Wiring Diagram - External LWCO” on
page 34 for typical wiring connections of the
LWCO to the boiler PCB.
WARNING
Electric Shock Hazard
ALWAYS check that the power to the boiler is
turned off before making the boiler may fail
and result in serious injury, or death if power
is supplied during wire connection. Product
failures caused by incorrect installation are not
covered by warranty.

19Installing the System Piping
Method 1.
External LWCO
Air Vent
Pressure
Relief Valve
Refer to the following illustration for a pressure relief
valve installation in the space heating system. Watts
174A pressure relief valve (
3
/
4
in, HV, Max 30 psi) is
provided with the boiler.
Pressure Relief
Valve
Method 2.
Note ●Depending on the installation
conditions, pressure relief valves (not
included and for separate purchase) of
up to 80 psi can be used.
Refer to“11.13.3 Setting the Operation
Parameters - 17. High Sys Pressure”on
page 111 to adjust the upper limit
pressure lockout setting when using a
higher rated valve.
●All separately purchased pressure
relief valves must be ASME certified.
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.
●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.

20 Installing the System Piping
3.1.3 Space Heating System Piping
When connecting the space heating system, follow these guidelines:
●Carefully tighten all connections to avoid damage to fittings.
●After installing the boiler, check the space heating system’s operation and inspect for leaks.
The optional Navien manifold system enables easy separation of the boiler (primary loop) from the system
(secondary loop(s)). Refer to the illustration below for an example of the piping connections for a Navien
manifold system (primary zone).
Space Heating Supply
Space Heating Return
The following tables list the specifications for the available pumps and Navien’s manifold system. If you are not
using one of the pumps listed below, you must use a circulator with check valve installed at pump outlet or a
pump with an integral check valve.
Model Number
Item NHB-055H NHB-080H NHB-110H NHB-150H
Manifold System GFFM-MSOZUS-001
Pump Specifications
Manufacturer NHB-055/080/110H NHB-150H
Grundfos UPS 15-58 UPS 26-99
Armstrong Astro 230CI Astro 280CI
Taco 0015-MSF3-IFC 0013-MSF2-IFC
Wilo Star S 21F TOP-S 1.25x25
Bell & Gossett NRF-25 NRF-36
Note If you are not using one of the pumps listed in the above tables, use a pump with an integral check
valve or install a check valve at the pump outlet. Refer to the performance curve on page 21 to
select a pump that suits your application. The boiler can supply up to a maximum of 2.5 A current at
the boiler pump connection terminal.