Navien NHB Series User manual

WARNING
If the information in these instructions is not followed exactly, a re or explosion may result, causing
property damage, personal injury, or death.
Do not store or use gasoline or other ammable 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 re department.
Installation and service must be performed by a qualied 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.
Keep this manual near this boiler for future
reference whenever maintenance or service
is required.
Installation & Operation Manual
NFB Condensing Boilers
Model
NFB-301C
NFB-399C

22
Requirements for the State of Massachusetts
NOTICE BEFORE INSTALLATION
This appliance must be installed by a licensed plumber or gas fitter in accordance with the Massachusetts Plumbing and Fuel Gas Code 248
CMR Sections 4.00 and 5.00.
IMPORTANT: In the State of Massachusetts (248 CMR 4.00 & 5.00)
For all side wall horizontally vented gas fueled equipment installed in every dwelling, building or structure used in whole or in part for
residential purposes, including those owned or operated by the Commonwealth and where the side wall exhaust vent termination is less than
seven (7) feet above finished grade in the area of the venting, including but not limited to decks and porches, the following requirements shall
be satisfied:
1. INSTALLATION OF CARBON MONOXIDE DETECTORS. No installation or replacement of a vented gas appliance shall be permitted unless a
battery powered or electrically hard wired carbon monoxide detector is present on the same floor as the appliance or on the next adjacent
floor when the appliance is located in a crawl space unless the appliance is located in a detached, uninhabitable garage. For all residential
dwellings, a carbon monoxide detector must also be present on each habitable level of the dwelling. These requirements shall not be
deemed to waive any additional requirements imposed by M.G.L. c. 148 §26F1/2.
2. APPROVED CARBON MONOXIDE DETECTORS. Each carbon monoxide detector as required in accordance with the above provisions shall
comply with NFPA 720 and be ANSI/UL 2034 listed and IAS certified.
3. SIGNAGE. Whenever any through-the-wall vent is installed less than seven feet above the finished grade, a metal or plastic identification
plate shall be permanently mounted to the exterior of the building at a minimum height of eight feet above grade directly in line with the
exhaust vent terminal. The sign shall read, in print size no less than 0.5 inches in size,“GAS VENT DIRECTLY BELOW. KEEP CLEAR OF ALL
OBSTRUCTIONS”.
4. INSPECTION. The state or local gas inspector of the side wall horizontally vented gas fueled equipment shall not approve the installation
unless, upon inspection, the inspector observes carbon monoxide detectors and signage installed in accordance with the provisions of
248 CMR 5.09 and 5.12.

3Contents
Contents
1. About the Boiler 6
1.1 Included Items 6
1.2 Accessories 6
1.3 Specifications 7
1.4 Components 9
1.5 Dimensions 11
1.6 Rating Plate 13
2. Installing the Boiler 14
2.1 Removing the Wood Pallet from the Boiler 14
2.2 Choosing an Installation Location 15
2.3 Mounting the Boiler to the Wall 17
3. Installing the System Piping 19
3.1 Installing a Space Heating System 19
3.2 Connecting the Condensate Drain 27
3.3 Filling the System 29
3.4 Testing the Water System 30
3.5 Considerations for System Applications 31
3.6 Examples of Electrical Connections 36
3.7 Connecting External devices (Field Wiring Guidelines) 45
4. Connecting the Gas Supply 47
4.1 Gas Pipe Sizing Tables 49
4.2 Measuring the Inlet Gas Pressure 50
5. Venting the Boiler 52
5.1 Selecting a Vent Type 54
5.2 Selecting Vent Pipe Materials 57
5.3 Measuring Vent Length 58
5.4 Terminating the Vent 58
5.5 Removing the Internal Air Filter 61
6. Setting the DIP Switches 63
6.1 DIP Switch 1 (6 switch unit) 63
6.2 DIP Switch 2 (8 switch unit) 63
7. Connecting the Power Supply 64
8. Installing a Cascade System 65
8.1 Connecting Water Supplies 65
8.2 Connecting the Communication Cables 71
9. Installing a Common Vent System 72
9.1 About the Common Vent System 72
9.2 Navien Backflow Damper (Back-draft Damper) 77
9.3 Starting the Common Vent System 78
9.4 Connecting and Terminating the Vent Pipe 81
9.5 Setting up the Common Vent System 82
9.6 Common Vent Termination Clearances 82
9.7 Installing a Condensate Drain 84
9.8 Exhaust Vent Termination Clearances (For Direct Vent) 85
9.9 Maintenance
86
10. Installation Checklist 87
11. Operating the Boiler 90
11.1 Turning the Boiler on or off 90
11.2 Adjusting the Temperature 91
11.3 About the Operating Status Information 92
11.4 Resetting the Boiler 92
11.5 Accessing Basic Menu Items 92
11.6 Accessing Advanced Menu Items 99
11.7 Understanding Error Codes 109
12. Appendixes 110
12.1 Gas & High Altitude Conversion 110
12.2 Wiring Diagram 116
12.3 Ladder Diagram 117
12.4 Outdoor Temperature Sensor 118
12.5 Outdoor Reset Control 119
12.6 Component Assembly Diagrams and Part Lists 120

4 Safety Information
The following safety symbols are used in this manual. Read and
follow all safety instructions in this manual precisely to avoid
unsafe operating conditions, fire, explosion, property damage,
personal injury, or death.
DANGER
Indicates an imminently hazardous situation which, if not
avoided, could result in severe injury or death.
WARNING
Indicates a potentially hazardous situation which, if not
avoided, could result in injury or death.
CAUTION
Indicates a potentially hazardous situation that, if not avoided,
could result in property damage.
DANGER
If you smell gas:
ƔDo not try to light any appliance.
ƔDo not touch any electrical switches or use landline phones.
ƔFrom a neighbor’s phone, call your gas provider and follow
their instructions.
ƔIf you cannot reach your gas provider, call the fire
department.
ƔDo 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.
ƔThe 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.
ƔVapors 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.
ƔKeep 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.
Safety Information

5Safety Information
CAUTION
ƔDo not turn on the boiler unless the water and gas
supplies are fully opened.
Doing so may damage the boiler.
ƔDo not use this boiler for anything other than its
intended purpose, as described in this manual.
ƔDo 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.
ƔWhen 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.
ƔDo not use unapproved replacement or accessory parts.
Doing so may result in improper or dangerous operation
and will void the manufacturer’s warranty.
ƔDo 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.
ƔThis 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
ƔDo not store or use gasoline or other flammable liquids
near this boiler.
Doing so may result in fire or explosion.
ƔDo not place combustibles, such as newspapers or
laundry, near the boiler or venting system.
Doing so may result in a fire.
ƔDo not place or use hair sprays, spray paints, or any other
compressed gases near the boiler or venting system,
including the vent termination.
Doing so may result in fire or explosion.
ƔDo 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.
ƔDo 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.
ƔDo not touch the power cord or internal components of
the boiler with wet hands.
Doing so may result in electric shock.
California law requires the following Prop 65 warning to be
provided:
WARNING
This product can expose you to chemicals including lead, lead
compounds, and carbon bisulfide which are known to the
State of California to cause cancer and birth defects or other
reproductive harm. For more information, go to
www.P65Warnings.ca.gov.

6 About the Boiler
1.1 Included Items
When you open the box, you will nd 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
3 in Vent Termination Caps (x2) 3 in Wall Flanges (x4)
Air Vent
Wall Mounting Bracket
(with Anti-Vibration Rubber Pad)
* Included in the L box
Tapping Screws & Anchors (x6) Pressure Relief Valve, Heating
Conversion Kit Outdoor Temperature Sensor and
Cable
Air Vent Bushing with Gasket
[1 in to in (NFB-301C)]
[1 in to in (NFB-399C)]
Condensate Trap
1. About the Boiler
Universal Temperature Sensor
(with Clip)
PRV-Air Vent Adapter
(with Clip)
Caps with Gaskets (x2) Double Nipple ( in to in)
1.2 Accessories
The following optional accessories are available for the boiler.
Light Commercial Neutralizer Kit Zone Controller
(FMZ-20/30)
Zone Controller
(FMZ-40/60)
Universal Temperature Sensor
(with clip)
Navi-Link
(Wi-Fi Control System) Modbus Gateway
Note The universal temperature sensor can be used as a
system temperature sensor or a DHW tank sensor.

7About 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 Commercial Condensing Boiler
Space Heating Ratings Other Specifications
Model
Number
1
Heating Input (MBH) Gross
Output
2
(MBH)
Net AHRI
Rating Water
3
(MBH)
Thermal
Efficiency
2
(%)
Boiler Water
Content
(Gallons)
Water
Pressure
Water
Connection Size
(Supply, Return)
Min. Max.
NFB-301C 20 301 293 255 97.5 7.6
12-160 psi
1¼ in NPT
NFB-399C 26 399 389 338 97.5 9.6 1½ in NPT
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.

8 About the Boiler
General Specifications
Item NFB-301C NFB-399C
Dimensions 25.1 in (W) × 22.3 in (D) × 32.8 in (H)
Boiler Weight 243 lb (110 kg) 278 lb (126 kg)
Boiler Weight with Water 307 lb (139 kg) 371 lb (168 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 -0.06 to -0.87 in WC -0.03 to -1.85 in WC
Propane Gas Manifold Pressure -0.01 to -0.92 in WC -0.01 to -0.90 in WC
Gas Connection Size
3
/
4
in NPT
Power Supply
Main Supply 120 V AC, 60 Hz
Maximum Power
Consumption Less than 12 amperes
Materials Casing Cold-rolled carbon steel
Heat Exchangers Stainless Steel
Venting
Exhaust 3 in or 4 in PVC, CPVC, approved polypropylene, approved stainless steel
3 in or 4 in Special Gas Vent Type BH (Class III, A/B/C)
Intake 3 in or 4 in PVC, CPVC, polypropylene, stainless steel
3 in or 4 in Special Gas Vent Type BH (Class III, A/B/C)
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
Temperature Setting Range
Item Temperature Setting Range Remarks
Space Heating
Supply 77–194°F (25-90°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 “11.5.2 Setting the Space Heating Operation” on
page 93.

9About 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
Air Intake Pipe
Exhaust
Optional Heating Return
Fan & Motor Assembly
Dual Venturi
Gas Pipe
PCB
24V Power Transformer
Power Switch
PRV-Air Vent Connection
(Optional Heating Supply)
Condensate Outlet
Mixing Chamber
Igniter
Flame Detector
Fire-Tube Type
Heat Exchanger
ASME Name Plate
Front Panel
APS
Gas Valve
Gas Inlet
Condensate Trap
(Siphon)

10 About the Boiler
Terminal Block
Dual Venturi
Fan & Motor Assembly
Optional Heating Return
Fire-Tube Type
Heat Exchanger
Gas Pipe
Power Switch
Heating Return
Gas Valve
ASME Name Plate
Mixing Chamber
Internal Air Filter
PRV-Air Vent Connection
(Optional Heating Supply)
Heating Supply
Condensate Trap
(Siphon)
PCB
Front Panel
APS
Air Intake Pipe

11About the Boiler
1.5 Dimensions
The following diagrams show the dimensions of the boiler and the table lists the supply connections.
32.8" (835 mm)
Supply Connections
Description Diameter
NFB-301C NFB-399C
A Air Intake 3 in
B Exhaust Gas Vent 3 in
CPRV-Air Vent Connection
(Optional Heating Supply) 1
1
/
4
in 1
1
/ in
D Optional Heating Return 1
1
/
4
in 1
1
/ in
E Heating Supply 1
1
/
4
in 1
1
/ in
F Condensate Outlet
3
/
4
in
G Heating Return 1
1
/
4
in 1
1
/ in
H Gas Connection
3
/
4
in
Overhead View
AB
C
D
4.9” (125 mm)
7.5” (191.3 mm) 10.7” (271 mm)
16.3” (412.6 mm)
25.2" (640 mm)
AB
C
D
4.8” (122 mm)
7.2” (184 mm) 10.6” (271 mm)
16.5" (420 mm)
25.1“ (640 mm)
<NFB-301C> <NFB-399C>

12 About the Boiler
Supply Connections
E G HF
12.7” (320.7 mm)
4” (102.3 mm)
18.9” (480.6 mm)
21” (534.2 mm)
22.4” (568 mm)
14.3” (364.4 mm)
8.5”
(217 mm)
25.2” (640 mm)
3.1”
(78.5 mm)
16.7”
(423.1 mm)
14.3” (362.1 mm)
EGHF
16.5” (420 mm)
3.2” (81 mm)
18.4” (468 mm)
22” (560 mm)
22.3” (566 mm)
17.2” (436 mm)
2.9 ”
(75 mm)
6.3”
(161 mm)
11.8” (301 mm)
5.3”
(136 mm)
25” (638 mm)
<NFB-301C> <NFB-399C>

13About the Boiler
1.6 Rating Plate
The Navien NFB boilers come from the factory congured 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 110 for details.
Installation procedures at normal manifold pressure. This appliance has also been tested up to 10,100 ft(3,078 m).
For installations at altitudes up to 10,100 ft(3,078 m), follow the directions provided in the High Altitude Installations sections
of the lnstallatlon Manual.
toutes les procédures d'installation à haute altitude CAN/CGA 2.17 à une pression normale. Cet appareil a été testé jusqu'à 10,100 pieds
(3.078 m). Pour les instructions d'installation à une altitude supérieure à 10.100 pieds, suivez les instructions fournies dans la section des
installations à haute altitude du manuel d'installation.
7
2017
389,000
338,000
WARNING
Ensure that the gas type and power source specications match what is listed on the rating plate. Using a dierent gas type will cause
abnormal combustion and boiler malfunction. Using abnormally high or low AC voltage may cause abnormal operation, and may reduce
the life expectancy of the product.
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
.

14 Installing the Boiler
2.1 Removing the Wood Pallet from the
Boiler
After you open the box, remove the wood pallet and the pallet
brackets and then install the boiler.
CAUTION
After opening the box, verify that all included accessories are
present in the accessory box and upper container.
Removing the Wood Pallet and the Pallet Brackets
1. Remove the L and R boxes.
Note Do not discard the L box, as it contains the wall-
mounting bracket and the anti-vibration rubber
pad.
2. Loosen the eight screws that secure the wood pallet on the
bottom left and right sides of the boiler.
3. Remove the wood pallet, the upper container, and the lower
pad.
Upper
Container
Lower Pad
Wood Pallet
4. Loosen the eight screws that secure the pallet brackets.
CAUTION
Keep the removed screws in a safe place. The screws will be
used again in Step 6.
2. Installing the Boiler

15Installing the Boiler
2.2 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:
Compliance Requirements
ƔLocal, state, provincial, and national codes, laws, regulations, and
ordinances.
ƔNational Fuel Gas Code, ANSI Z223.1-latest edition.
ƔStandard for Controls and Safety Devices for Automatically Fired
Boilers, ANSI/ASME CSD-1, when required.
ƔNational Electrical Code.
ƔFor 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
ƔWater – the installation location should be near where the
domestic water supply enters the building.
ƔGas – the installation location should be near where the gas
supply enters the building.
ƔElectricity – 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. Excess water 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.
Flooring
The boiler must not be installed on carpeting.
WARNING
Do not install a boiler on carpeting even if a foundation is used.
Fire can result in severe personal injury, death, or substantial
property damage.
5. Remove the two pallet brackets.
6. Tighten the eight screws into the original position.
CAUTION
Ensure that the screws have been retightened. If you do not
retighten the screws, the boiler’s airtightness will decrease.

16 Installing the Boiler
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 27.
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.
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 the Boiler” on page 52.
To ensure adequate venting and ventilation, follow these
guidelines:
ƔMaintain proper clearances from any openings in the building.
ƔInstall the boiler with a minimum clearance of 12 in (305 mm)
above the level required by local codes and weather conditions.
ƔMaintain a minimum clearance of 4 ft (1.2 m) from heating and
cooling vents.
ƔDo not enclose the vent termination.
ƔInstall the exhaust vent in an area that is free from any
obstructions, where the exhaust will not accumulate.
ƔDo not install the boiler where moisture from the exhaust may
discolor or damage walls.
ƔDo not install the boiler in bathrooms, bedrooms, or any other
occupied rooms that are normally kept closed or not adequately
ventilated.
Adequate Installation Clearances
CAUTION
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 12 in (305 mm) minimum
Back 0.5 in (13 mm) minimum
Front 24 in (610 mm) minimum
Sides 6 in (152 mm) minimum
Bottom 16 in (406 mm) minimum

17Installing the Boiler
2. Mount the wall bracket and the boiler following the
instructions below for your installation type.
ƔMounting to a wood studded wall:
Mount the wall bracket using the lag bolts provided.
ƔMounting to a concrete wall:
Mount the wall bracket using the anchor bolts provided.
To mount the anchor bolts, drill a 3/8" diameter hole 3-1/2"
deep and insert anchor.
ƔMounting to a metal studded wall:
Mount the wall bracket using eld supplied toggle bolts
capable of supporting 100 pounds each.
Note ƔThe wall bracket and the anti-vibration rubber
pad are contained in the L box.
ƔThe product should be installed horizontally.
ƔAll 4 holes of the wall bracket must be inserted
with the anchor bolts to ax the bracket.
ƔThe anti-vibration rubber pad must be located
between the wall and the bracket.
ƔThe anti-vibration rubber pad must be mounted
with its arrow mark ( ) facing outward.
CAUTION
It is necessary to leave clearance for service access.
Clean, Debris and Chemical-free Combustion Air
ƔDo not install the boiler in areas where dust and debris may
accumulate or where hair sprays, spray detergents, chlorine, or
similar chemicals are used.
ƔDo not install the boiler in areas where gasoline or other
ammables are used or stored.
ƔEnsure 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.
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” for the appropriate altitude setting.
2.3 Mounting the Boiler to the Wall
Ensure the wall for which the boiler is intended to be mounted is
composed of either, cement, brick, block or wooden studs spaced
16 inches apart from center.
Ensure the wall is capable of supporting at least 400 pounds for
the NFB-399C model. (350 pounds for the NFB-301C)
To mount the boiler to the wall:
1. Remove the wall bracket from the L box.

18 Installing the Boiler
WARNING
ƔThe 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. It is recommended
to use a lifting device when lifting the product. The
maximum load of the device should be based on the weight
of the appliance with water.
ƔDo 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.
ƔIf a separate installation structure is provided, it must be
fixed on the floor with a stud.
ƔMake sure that the wall bracket is installed horizontally
using a spirit level.
ƔBe careful not to drop any foreign objects into the intake or
exhaust vents during installation.
CAUTION
Do not mount the boiler to drywall that has not been
reinforced.

19Installing 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.
WARNING
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.
3.1 Installing a Space Heating System
The fire-tube type heat exchanger of the Navien NFB boiler is
designed to attain the highest level of heat transfer in a compact
design. To accomplish this, the heated gas flows through a series
of small-diameter tubes, maximizing the heat transfer area. To
maintain the efficient and reliable operation of the heat exchanger,
and to avoid heat exchanger failure, it is critical to ensure the rules
and guidelines in this section are followed.
CAUTION
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. Installing the System Piping
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
ƔFreeze 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.
ƔBefore using freeze protection products, ensure that system
fluid contains proper glycol concentration and the inhibitor level
is appropriate. Navien recommends against exceeding a 50%
concentration of glycol.
ƔWhen 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.
ƔWhen using the freeze protection products, allowance should be
made for expansion of the glycol solution.
ƔFreeze damage is not covered by the warranty.
ƔThe use of glycol results in a greater head loss due to its higher
viscosity compared to water. See page 26 for additional
information regarding the use of glycol.
WARNING
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
ƔThe Navien NFB boiler is intended solely for use in pressurized
closed loop heating systems operating with 12-160 psi water
pressure at the boiler outlet. To obtain the minimum system
design pressure, follow the piping diagrams illustrated in this
section.
ƔThe Navien NFB 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.

20 Installing the System Piping
Oxygen Elimination
This boiler may only be installed in a pressurized closed-loop
heating system, free of air (oxygen) and other impurities. To avoid
the presence of oxygen, ensure all of the air is removed from
the system during commissioning via strategically placed and
adequately sized air removal devices, 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.
WARNING
ƔImmediately 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.
ƔFailure to follow these instructions may result in poor
performance, unnecessary wear of system components and
premature failure.
CAUTION
Do not solder piping directly onto the water connections,
as the heat may cause damage to internal components. Use
threaded water connections only.
3.1.2 Essential Elements in a Space Heating System
Boiler Piping Options
The following illustrations show various boiler piping options.
Pressure Relief
Valve
Auto Air Vent
Supply
Return
<Supply / Return Bottom>
Pressure Relief Valve
Air Vent Bushing
Double Nipple
Tee
Auto Air Vent
Supply
Return
<Supply Top / Return Bottom>