RBI FUTERA XLF Series Use and maintenance manual

Copyright 2019Mestek, Inc.
Futera III Boiler manual or
Futera Fusion Boiler manual or
Futera XLF Boiler manual
This manual is intended only for use by a qualified heating installer/technician. Read and follow this manual, all
supplements and related instructional information provided with the boiler. Install, start and service the boiler only
in the sequence and methods given in these instructions. Failure to do so can result in severe personal injury,
death or substantial property damage.
Do not use the boiler during construction. Construction dust and particulate, particularly drywall dust, will cause
contamination of the burner, resulting in possible severe personal injury, death or substantial property damage.
The boiler can only be operated with a dust-free air supply. Follow the instruction manual procedures to duct air to
the boiler air intake. If the boiler has been contaminated by operation with contaminated air, follow the instruction
manual guidelines to clean, repair or replace the boiler if necessary.
Affix these instructions near to the boiler. Instruct the building owner to retain the instructions for future use by a
qua hnician, and to follow all guidelines in the User’s Information Manual.
82-0400
V3HN-I0M-3
HeatNet®V3
ControlManual
Control adjustment and operation instructions
for firmware versions Version 3.x
This instruction manual applies only to version 3.x
firmware on version 3.x control boards. Current
firmware is backwards compatible with version 2.x
boards, but some current features may not be
available. To replace firmware on an existing
boiler, contact the factory or website
http://www.rbiwaterheaters.com to obtain the
original firmware file or for assistance in applying
current firmware to an older version control board.
Also read and follow:

Information contained in this publication regarding device applications and the like
is provided only for your convenience and may be superseded by updates. It is your
responsibility to ensure that your application meets with your specifications.
RBI MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND
WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR
OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT
LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE,
MERCHANTABILITY OR FITNESS FOR PURPOSE.
http://www.rbiwaterheaters.com/
The RBI name and logo, Mestek name and logo, Futera, HeatNet, and H-
Net name and logo are registered trademarks of Mestek, Incorporated in the
U.S.A. and other countries.
BACnet is a registered trademark of ASHRAE. LonWorks is a registered
trademark of Echelon Corporation. All trademarks mentioned herein are
property of their respective companies.
© 2019, Mestek Technology Incorporated, Printed in the U.S.A., All Rights
Reserved.

TABLE OF CONTENTS
Page 3
Table of Contents
TABLE OF CONTENTS ..............................................................................................................................3
Introduction................................................................................................................................................5
THE FUTERA III/FUSION-SERIES V3 HEATNET CONTROL .......................................................................................................................5
Features & Specifications.........................................................................................................................7
STANDARD FEATURES OVERVIEW........................................................................................................................................................7
Specifications ............................................................................................................................................9
Components & Accessories ...................................................................................................................10
Setup & Operation ................................................................................................................................... 11
BASIC MULTI BOILER SYSTEM OPERATION..........................................................................................................................................11
MIXED BOILER TYPES USING PRIORITY SETS .....................................................................................................................................12
MIXED BOILER SYSTEM OPERATION...................................................................................................................................................12
START/STOP PRIORITY CONDITIONS..................................................................................................................................................14
SELECTING MIXED BOILERS ..............................................................................................................................................................15
MIXED SYSTEM TYPE 1: HIGH SYSTEM TURNDOWN ............................................................................................................................15
MIXED SYSTEM TYPE 2: CONDENSING /NON-CONDENSING..................................................................................................................18
Heating Control Methods ........................................................................................................................ 22
HEATING METHOD 1.........................................................................................................................................................................22
HEATING METHOD 2.........................................................................................................................................................................22
HEATING METHOD 3.........................................................................................................................................................................22
HEATING METHOD 4.........................................................................................................................................................................22
HEATING METHOD 5.........................................................................................................................................................................22
OPERATING LIMIT.............................................................................................................................................................................22
INPUT PRIORITIES ............................................................................................................................................................................22
HEATING METHOD 1HEAT DEMAND ..............................................................................................................................................23
HEATING METHOD 2STAGE CONTROL T1-T2...................................................................................................................................23
HEATING METHOD 34-20MACONTROL .............................................................................................................................................24
HEATING METHOD 4AA INPUT ..........................................................................................................................................................24
HEATING METHOD 5MODBUS COMMUNICATIONS..............................................................................................................................24
BASE LOADING,RELAY CONTROL......................................................................................................................................................25
SETTING UP BASE LOADING ...............................................................................................................................................................28
Domestic Hot Water Methods .................................................................................................................28
DHW MAXIMUM RUNTIME.................................................................................................................................................................29
DHW METHOD 1:DHW HEATING ONLYUSING A DHW MASTER AND MEMBERBOILER(S)EMPLOYING H-NET ..................................30
DHW METHOD 2:FAILSAFE COMBINATION DHW AND SPACE HEATING WITH A MASTER BOILER AND MEMBER BOILERS UTILIZING VALVES
(MASTER TYPE:COMBINATION) ......................................................................................................................................................34
DHW METHOD 2:FAILSAFE COMBINATION DHW AND SPACE HEATING WITH A MASTER BOILER AND MEMBER BOILERS UTILIZING PUMPS
(MASTER TYPE:COMBINATION) ......................................................................................................................................................36
DHW METHOD 3:DHW HEATING ONLY,USING A HEADER SENSOR INPUT ...........................................................................................40
DHW METHOD 4A:SPACE HEATING WITH DHW OVERRIDE OF SETPOINT ON MASTER, USING AN AQUASTAT .........................................43
DHW METHOD 4B:SPACE HEATING WITH DHW OVERRIDE OF SETPOINT ON MASTER, USING A DHW 10K TANK SENSOR .....................46
DHWMETHOD 5A:LOCAL DHW TANK HEATING USING A 10K TANK SENSOR........................................................................................49
DHW METHOD 5B:LOCAL DHW TANK HEATING USING A THERMOSTAT &HYBRID SENSOR....................................................................53
DHW METHOD 6:DHW USING DIRECT CONTROL (NOT PREFERRED).................................................................................................55
Using the 4-20mA input (OPTIONAL) .....................................................................................................55
SETPOINT PRIORITIES.......................................................................................................................................................................57
Circulator Pump Options ........................................................................................................................57
Local Pump Option..................................................................................................................................59

TABLE OF CONTENTS HeatNet Control V3
Page 4
Auxiliary Function Options..................................................................................................................... 59
Outdoor Reset ......................................................................................................................................... 60
Sensors.................................................................................................................................................... 60
Stack Temperature .................................................................................................................................. 60
Security.................................................................................................................................................... 61
Save/Restore Configuration Settings..................................................................................................... 61
USB Features........................................................................................................................................... 61
Saving/Restoring Settings...................................................................................................................... 61
Diagnostics.............................................................................................................................................. 61
Communications ..................................................................................................................................... 62
Failsafe Modes......................................................................................................................................... 62
FAILSAFE REQUIREMENTS:................................................................................................................................................................62
Category 1 Venting.................................................................................................................................. 63
Limited Flow Boiler Control Options...................................................................................................... 63
HeatNet Online......................................................................................................................................... 65
Wiring Connections................................................................................................................................. 66
* Status Information ................................................................................................................................ 78
STATUS INFORMATION SCREENS ........................................................................................................................................................78
Status Screen Fault Display.................................................................................................................... 80
Calibration................................................................................................................................................ 83
Log Entry.................................................................................................................................................. 84
Line 4 Log Entries:.................................................................................................................................. 85
Default Settings & Menu Item Descriptions —SETUP.......................................................................... 88
Default Settings & Menu Item Descriptions —ADVANCED SETUP..................................................... 94
MODBUS Communications................................................................................................................... 101
Troubleshooting.................................................................................................................................... 112
Futera III/Fusion-Series HeatNet Control Run Screen......................................................................... 117
Futera III/Fusion-Series HeatNet V3 Control Menu Tree ..................................................................... 119
Futera III/Fusion HeatNet V3 Control Advanced Menu Tree ............................................................... 120
Worksheet.............................................................................................................................................. 121

FEATURES & SPECIFICATIONS HeatNet Control V3
Page 5
Introduction
The Futera III/Fusion-Series V3
HeatNet Control
The Futera III/Fusion-Series V3 boiler control is the third
generation of the HeatNet control platform. Control
hardware has been added to make use of many new heating
applications. These new features are outlined in the Features
& Specifications section.
Two versions of the Control are available. The full version
and the “Lite”version. The Full version is available as an
option. Consult the factory or sales. The Lite version:
1.) Supports (1) system pump
2.) HeatNet Online monitoring requires a Touchscreen
display on the Master boiler (Full and Lite).
3.) Only a 0-10 VDC output (no 4-20mA)
4.) Does not support (3) alternate staging relays
5.) Pluggable colored terminal strips.
The Futera III/Fusion-Series boiler control is designed to
provide the Futera III/Fusion-Series of boilers with an
integrated boiler management system on every boiler.
Designed for the Air-Fuel coupled Futera III/Fusion-Series
boilers, the Futera III/Fusion-Series HeatNet control
provides for optimized heating efficiency without the need
for a “wall mount control”. Since the Futera III/Fusion-
Series modular control method is based on digital
communications, analog control signals are not required.
Although the use of analog control signals is still supported
(4-20mA control loops and 0-10vdc control voltages), a
higher level of control precision, repeatability, and feedback
is gained with digital communications control.
With the Futera III/Fusion-Series, optimized heating
efficiency is accomplished by setting the Modulation
Maximum (Mod-Max) setting to exploit the inverse
efficiency curve. This value can be adjusted so that as each
boiler is added, it operates at its maximum turndown. This
allows the maximum number of boilers to operate at their
lowest inputs, until all boilers are firing. Once all boilers are
firing, full range modulation control is allowed. An outdoor
reset function is also provided to assist in the optimized
heating efficiency of the Futera III/Fusion-Series boilers.
The Futera III/Fusion-Series boiler with the Futera
III/Fusion-Series H-Net control, can be operated in multiple
ways:
1. As a standalone boiler.
2. A boiler, in a Boiler Network, using the HeatNet®
(H-Net®) protocol.
3. A Member boiler to a boiler management system with
multiple input control methods.
The primary purpose of the control is to maintain the boiler
water temperature at the supply or the header sensor using a
target setpoint. While performing this task, the control also
monitors dedicated external limits in a limit string and
provides an orderly shutdown and fault indication in the
event of a tripped limit. The monitored limits include a
HIGH LIMIT AQUASTAT, LOW WATER CUTOFF,
GAS PRESSURE, FLOW, IGNITION CONTROL fault,
GAS VALVE alarm, VARIABLE FREQUENCY DRIVE
alarm, and other optional or user selectable limits.
The HIGH LIMIT circuit is independent of
the control and shuts down the ignition
control and the boiler if the control board or
other component of the boiler was to
malfunction. The control will continue to
function and report the fault, but its ability to
control the boiler will end.
Each Futera III/Fusion-Series boiler employing this control
can function as either a Master or a Member. This allows
one boiler (Master) to be in control of a target temperature.
The other boilers (Members) only respond to the commands
issued by the Master. If using an external control, all boilers
can be setup as Member s. The following will define the
roles of Master and Member.
Master
A boiler becomes a Master when a temperature sensor is
connected to the J10 “SYSTEM HEADER” terminals. The
sensor is auto-detected.
The Master senses and controls the common system
header/loop water temperature using a system setpoint. It
uses any boilers it finds (over the H-Net communications
cable) to accomplish this. It can also monitor the Outside
Air (OA) temperature to provide outdoor reset functionality.
Only one Master is allowed in a system.
When operating as a Master, the boiler provides a control
method using a PID algorithm to regulate water
temperature. This algorithm allows a single boiler (Master),
or multiple (Master + Member) boilers. There are two PID
algorithms that can be used. One PID is used for space
heating, and the other for Domestic Hot Water (DHW)
heating. This allows both space and DHW to be controlled
simultaneously.

FEATURES & SPECIFICATIONS HeatNet Control V3
Page 6
Figure 1 Heat band
The control algorithm is based upon a Heat Band, at the
center of which is the setpoint. While below the Heat Band,
boilers are staged on and modulated up until the Heat Band
is entered. Once in the Heat Band, modulation is used to
maintain setpoint. Boilers are shut down only when the top
of the Heat Band is breached. Timers are also used to
prevent short cycling.
The control algorithm is based upon a Heat Band, at the
center of which is the setpoint. While below the Heat Band,
boilers are staged on and modulated up until the Heat Band
is entered. Once in the Heat Band, modulation is used to
maintain setpoint. Boilers are shut down only when the top
of the Heat Band is breached. Timers are also used to
prevent short cycling.
While staging the boilers on, a modulation clamp
ADVANCED SETUP: MODULAR BOILER SET:
MOD MAX-LAST FIRE is used to hold the boilers at a
lower fire rate until the last boiler is fired. Once the last
boiler fires, the modulation clamp is removed and all boilers
are allowed to fire above this clamped percentage up to
100%. This “boiler efficiency” clamp is defaulted to 70%
and thus limits all of the boilers individual outputs to 70%
until the last boiler fires. All running boilers modulate up
and down together, always at the same modulation rate. As
a general rule, this percentage should be no lower than twice
the minimum turndown to minimize short cycling.
When additional boilers are needed to achieve setpoint in
the system, the Master boiler employs an ADAPTIVE
MODULATION algorithm to prevent over firing of the
system. The Master communicates over the H-Net to view
the exact status of each Member boiler. When a new boiler
is added, the Master boiler adjusts the system modulation
rate lower to compensate for the BTUs that will be
introduced by the newly added boiler. This adjustment
occurs when the newly added Member boiler enters its ON
CALL state (default setting). This can be changed to PILOT
when the new boiler is called using the menu:
ADVANCED SETUP: ADAPTIVE MOD: DROP
DOWN. Once the Main Valve (on the newly added boiler)
is opened, and the DELAY RELEASE timer equals zero,
the PID algorithm is allowed to control the system
modulation. Setting the DELAY RELEASE timer will
allow some “soak” time of the newly added boiler before
releasing modulation control to the PID.
The ADAPTIVE MOD menus are disabled
on a Member boiler, but are still visible.
Member
If a “SYS/DHW HEADER” sensor is not connected to J10,
a boiler always defaults to the role of Member.
The Member boiler can operate as part of a multi-boiler
system or as a standalone unit.
In a multi-boiler system the Member typically receives its
command signals from a designated Master-boiler. It is also
capable of receiving inputs from an external control system.
The boiler responds to these signals, to start/stop the burner,
and/or to modulate the firing rate. The outlet water
temperature is also monitored. If the outlet temperature
approaches the operating limit temperature setpoint
(adjustable), the boilers firing rate is limited and its
modulation value is reduced to minimize short-cycling. If
the operating limit is exceeded, or if an interlock trips, the
boiler is shut down. When connected with a network cable,
in a Master/Member role, the Members' status is
interrogated by the Master boiler.
Any standalone boiler will perform
better when controlling to a header sensor.
A Fusion, as a standalone boiler,
requires a header sensor to control properly.
In a standalone installation the Member typically receives
its command signals internally and operates based upon the
outlet water temperature input and the established settings in
the menu (Local Set-point) to start/stop the burner, and/or to
modulate the firing rate. If the operating limit is exceeded,
or if an interlock trips, the boiler is shut down. As in a
multi-boiler system, a standalone Member boiler is also
capable of receiving inputs from an external control system.
When using the H-Net network cable in a Master/Member
system, the system setpoint is sent from the Master as a
digital signal, along with the modulation value to control
firing rate. It also receives its command to start or stop over
the H-Net cable. Also, the SYSTEM CLOCK only needs to
be set on the MASTER. The Master will then set the time
on all Member boilers.
If not using the H-Net protocol (cable), an external control
can send a 4-20mA or 0-10V signal along with a 4-20mA
enable signal to control the setpoint or firing rate. The boiler
may also be treated as a 2-stage boiler or an ON-OFF boiler
using the dedicated T-inputs.

FEATURES & SPECIFICATIONS HeatNet Control V3
Page 7
Features & Specifications
HeatNet Version 3.x Discontinued
Features
1. With this hardware release the service power, switched
power, and the power switch connector have been
removed. These were available on prior versions of the
HeatNet control. Upgrading to this control from prior
versions will require some wiring changes using an
upgrade kit.
2. The J10B input is no longer supported for proving the
damper. Damper proving switches will need to be wired
to J12B, 7 & 8.
3. If a stack sensor is used with this version, the alarm
silence switch cannot be connected and the
disconnected wires should be terminated appropriately.
Silencing the alarm can be done by holding the BACK
and SELECT keys down at the same time.
Hardware Version 3.x Control
Additional Features
(Identified by circuit board color: BLACK)
1. Support for (2) Circulator pumps (1 if Lite version).
Two rotation modes are provided: Based on system
runtime or system pump runtime hours. Pump failure
switchover/retry mode.
2. Warm weather shutdown, (2) pump jog (1 if Lite
version) and local pump jog to keep pumps from
seizing.
3. The Modbus, BACnet or LonWorks communications
port can be accessed concurrently with the USB port
(HeatNet Control Pro). The BACnet, LonWorks, or
Modbus connections do not need to be disabled to use
the USB ports.
4. The DHW pump and the Local Pump relay connections
now provide a normally closed contact. This allows for
the use of a power open/power close valve.
5. Support for 5mA 0-10v control signals using third party
controls.
6. Support for (2) display types: Vacuum Florescent and
Color LCD using the same 20 pin ribbon cable. The
color LCD provides an interface for the HeatNet Online
monitoring.
7. System Return sensor input.
8. Enhanced boot loader and firmware storage. One
firmware storage location for user updates. One
firmware program that always remains resident so that a
factory program can be restored. Primary loading is
with a flashdrive. The P3 shunt restores the previous
firmware.
9. 32 bit Microcontroller operating @ 64 Mhz with 5-
stage pipeline, and prefetch cache.
10. (3) Stage control relay outputs for TBD applications.
11. Backwards compatible with existing HeatNet versions
1.x and 2.x controls and applications.
12. Support for 135 Ohm control actuators.
13. 1k Platinum Stack sensor.
14. Flow meter input or BMS GPM input/control
15. Dual PID controls. One for space heating and one for
DHW heating. Allows for simultaneous DHW/Space
heating.
Standard Features Overview
1. Five levels of external control inputs, including
modulation and staging that provide application
flexibility.
2. Digital Communications Control (analog 4-20mA and
0-10vdc control supported, but not required).
a. Boiler to Boiler : HeatNet (H-Net)
b. Building Management System (MODBUS,
Optional BACnet or LonWorks) to Boiler
3. Distributed control using the HeatNet (H-Net) protocol
for up to 16 boilers. Eliminates the need for “wall
mounted” controls.
4. Analog Control 4-20mA and 0-10vdc (5mA minimum
current) signals supported.
5. System/Boiler operating status text display
6. Interlock, Event, and System logging with a time
stamp.
7. Advanced PID algorithm optimized for the Futera
III/Fusion-Series boilers.
8. (4) Dedicated temperature sensor inputs for: Outside
Air Temperature, Supply (Boiler Outlet) Temperature,
Return (Boiler Inlet) Temperature, and Header
(Common System Supply) Temperature.

FEATURES & SPECIFICATIONS HeatNet Control V3
Page 8
9. Automatically detects the optional temperature sensors
on power up (Outdoor Air Temp sensor is enabled in
the settings menu).
10. Menu driven calibration and setup menus with a bright
(Adj.) 4 line Vacuum Fluorescent Display.
11. (8) Dedicated 24vac interlock monitors, and 8 dedicated
120vac system monitors used for diagnostics and
providing feedback of faults and system status.
12. Multiple circulator pump control modes.
13. Combustion Air Damper control with proof time,
support for a common combustion air damper.
14. USB/RS485 network plug-in to allow firmware updates
or custom configurations.
15. Optional BACnet or LonWorks interface.
16. Alarm Relay dry contacts, and Audible Alarm.
17. Runtime hours, and Cycles (based on Main Valve
Open).
18. Outdoor Air Reset with programmable setpoint and
ratio.
19. Time of Day clock to provide up to (4) night setback
temperatures.
20. Failsafe mode when a Building Management System is
controlling setpoint. If communications is lost, the
boiler/system automatically transfers to local boiler
setpoint control.
21. Rotation Methods (Lead-Lag): True Rotation (based on
boiler runtime) is default. First-On First-Off (FOFO),
Last-On First-Off (LOFO) and MIXED are optional.
22. Programmable password protection to secure the
programmable settings.
23. Remote 4-20mA setpoint control using a mapped
setpoint range to the 4-20mA control signal.
24. Freeze Protection allowing automatic starting of
boiler(s) using (2) Failsafe modes.
25. Adaptive Modulation. When additional boilers are
called, the Master adjusts all boilers fire rates to
compensate.
26. Mixed boiler types in a system.
27. Support for Domestic Hot Water (DHW) using a 10k
Sensor or a dry contact input from a tank thermostat.
28. Domestic Hot Water relay for use with a pump or
valve.
29. On-board power and socket for Protocessor
BACnet/LonWorks module.
30. HI/LO relay control option from connector J4
31. Resettable Fused interlock power circuit.
32. Additional terminal connector for H-Net shielded cable.
33. Backwards compatible to Version 1.x hardware.
34. Communications board integrated with the main board
from version 1.x control.
35. Base Loading of (1) boiler.
36. Domestic Hot Water time out for maximum DHW
runtime.

FEATURES & SPECIFICATIONS HeatNet Control V3
Page 9
Specifications
Control Microprocessor based PID modulating control (NOT a safety limit)
Environment -40 °F to 140 °F, <90% RH non-condensing
Input Power 24 VAC, 500 mA
Relays 1 System Pump (Lite version), 2 System Pumps (Full Version), Damper, Circulator, Alarm, DHW
Pump (v2.x), 8A 250 VAC resistive* - Refer to wiring diagram for application specific ratings
K8 on J4.2 &.6 for Base Loading
AC Interlocks 24 VAC –120 VAC input
Control Inputs AA, Heat Demand, 4-20mA Enable, OA override, T1-T2 (dry contact inputs)
4-20mA, 0-10 VDC
Dimensions 9” wide: 6” high: 2” deep
Temperature Sensors NTC thermistor, 10K @ 77 °F, 335.67K @ -40 °F, 185 @ 150 °F ,+/- 1 F
USB 1.0
RS485 MODBUS Modbus RTU
Boiler-to-Boiler HeatNet (H-Net)
Network Optional LonWorks, BACnet available bridge to MODBUS port

FEATURES & SPECIFICATIONS HeatNet Control V3
Page 10
Components & Accessories
Part Number
Component Description
16-0046
Futera III/Fusion-Series Control Board Version 3.x Full- Optional
16-0047
Futera III/Fusion-Series Control Board Version 3.x Lite - Standard
40-0088
Graphics Display Board
40-0091
Graphics Display, Color Touchscreen (HeatNet Online Interface)
16-0026
Temperature probe (bullet type, 1x.250 inch) ACI/10K-CP-BP
14-0325
Supply, Header, Return Sensors ACI 10k-CP-I-NW
14-0328
ACI-X/(2) CP-PO-4 4” probe with dual sensor
14-0329
ACI-X/(2) CP-PO-6 6” probe with dual sensor
13-0104
3”Immersion Well
14-0319
Outside Air Sensor with Housing ACI 10k-CP-O
Installation & Operation Manual
44-0060
RJ45 Communications Cable Assembly, 25 feet
40-0115
Ribbon Cable Assembly (Display Control)
44-0061
USB Cable Assembly, 6ft
14-0354
MODBUS to BACnet Bridge
14-0353
MODBUS to LonWorks Bridge
14-0356
MODBUS to HeatNet Online Module

SETUP & OPERATION HeatNet Control V3
Page 11
SETUP & OPERATION
Basic Multi Boiler System Operation
For boiler system setup/installations please
refer to Refer to the 2008 ASHRAE
Handbook, CH12 or later revision.
A basic multi boiler system typically uses boilers of the
same size and type. With HeatNet, this includes (1) Master
and (1-15) Member boilers. The boilers are connected
together using an H-Net communications cable effectively
creating (1) boiler. This allows the system heating BTUs to
be evenly distributed among all of the boilers. (See:, Typical
Single Boiler System, page 74).
Figure 2 Basic multiple boiler system
A basic multi boiler system can be configured using the
boiler menus to create custom systems/features. These
features are best described in the section: Default Settings
& Menu Item Description. Along with these menu
items are hardware support for many auxiliary
functions.
Once the system has been properly setup (all default menu
values used and H-Net addresses assigned), the system is
enabled by placing the REMOTE/LOCAL switch to the
LOCAL position on the Master boiler. All Member boilers
must have their respective switches in the REMOTE
position. When the Master boiler’s Heat Demand input
(LOCAL switch) closes, the system becomes operational
and will fire as many boilers as it needs to maintain the
header water temperature’s setpoint. See the DHW section
to fire to two setpoints.
When a boiler is to be fired in a multi boiler system (header
water temperature is below the heating band), the Master
checks the HeatNet boilers it has available. Then the Master
checks if a Lead Boiler is to be used (LEAD BOILER > 0).
The Master boiler then looks at which type of firing rotation
it has selected: LOFO, FOFO, TRUE (runtime), or MIXED.
In our example we will use the TRUE (runtime) rotation
since it is the default.
The Master now checks all of the runtimes to determine
which boiler has the least runtime based on the MIN
RUNTIME setting in ADVANCED SETUP: FIRING
MODE:. The MIN RUNTIME setting is the minimum
runtime interval in hours that is used to compare boiler to
boiler runtimes.
Once the boiler to fire has been determined, the Master
sends the command over the H-Net cable to fire that boiler,
and resets the ADD BOILER delay timer to prepare for the
next boiler to fire. If the header water temperature is still
below the heating band, and the ADD BOILER delay timer
has expired to zero, the process is repeated until the header
water temperature enters the heating band.
When a boiler receives a command to fire:
1. The system pump relay is enabled and the H-Net
control displays 'Flow Wait' until the flow-switch closes
between J11A, 1 & 2 within the programmed time
(10seconds).
2. All elements in the interlock string, terminated between
J11A and J11B, must be closed before the sequence is
allowed to continue.
3. If all interlocks are closed relay K5 is enabled to
command the combustion-air damper open (if used).
The H-Net control displays 'Damp: Wait' until the
damper end switch closes on input DAMPER, J12B.
4. Relay K6 is enabled energizing the local pump (if
used). The H-Net control commences its 'Flow-Wait'
timer (adjustable 10–240 sec.). The flow switch contact
is checked on terminals J11B, 5 & 6.
5. With all the interlocks closed, the boiler start relay K1
is enabled and energizes terminal 6 on the ignition
control. This signal is present on J5 Boiler Start
Operator.
6. The ignition control begins its cycle and provides an
output signal from terminal 4 to the H-Net control J5
Blower. The H-Net control responds and provides an
output signal to the VFD which sets the blower to the
programmed pre-purge speed.
7. After air-flow is established the ignition control waits
for the air switch to close. When the air switch closes it
provides an input to terminal 7 and pre-purge timing
commences. The H-Net display indicates 'Pre Purge'.
8. When purge is complete the ignition control energizes
the pilot gas valve from terminal 8, and the spark
generator from terminal 10, beginning a 10-second Pilot
Flame Establishing Period (PFEP). The H-Net control
responds to J5 Pilot Valve and provides an output
signal to the VFD which sets the blower to the
programmed ignition speed. The H-Net display
indicates 'Pilot'.
9. At the end of the PFEP the spark generator is de-
energized. If the pilot flame is detected, by the UV
scanner, the ignition control energizes the main gas
valve from terminal 9 to J5 Main Valve. The H-Net
display indicates 'Run'.

SETUP & OPERATION HeatNet Control V3
Page 12
10. If main-flame is detected the H-Net control holds the
burner at the low-fire rate for the MODULATION
DELAY time period. After this timer expires, the PID
allows the boiler to modulate and places the boiler into
the running state.
As boilers are added to the system settings in the ADVANCED
SETUP: ADAPTIVE MOD: DROP DOWN menu determines
when the modulation rate drops down to compensate for the
newly added BTUs. For the drop down to be active, one
boiler needs to be running when a new boiler is added (see:
Introduction: The Futera III/Fusion-Series H-Net Control:
Master).
If all boilers are firing, the modulation rate is released to go
to 100%. If all boilers are not firing, the modulation is
limited to the MOD-MAX clamp value. The MOD-MAX
clamp is used to keep the boilers running as efficiently as
possible. The following Mixed Boiler System Operation:
Selecting Mixed Boilers section outlines this with examples.
NOTE: If the boiler is running as a standalone boiler or
is direct modulated (including the AA input),
the MOD-MAX clamp will also be in effect
for the ADD BOILER DELAY time. This is to
minimize thermal shock to the boiler.
Once the header water temperature is in the heating band,
only the modulation rate is used to achieve the target
setpoint. The system will maintain the setpoint until the load
demand increases or decreases.
As the load decreases, the header water temperature will
start approaching the top of the band. The PID now lowers
the modulation rate to the boilers, attempting to keep the
temperature within the heating band. If the system is
delivering too many BTUs, the water temperature will cross
the top of the heating band.
When the header water temperature first exceeds the top of
the heating band, the boilers are again checked for the one
with the most runtime. The selected boiler will turn off
immediately and a shed boiler delay timer will be loaded
with the delay time. This time will need to expire before the
next boiler will be stopped, but only if the header water
temperature remains above the heating band. This timer is
used to allow the header water temperature to return back
into the band when a boiler is stopped. When a boiler is
stopped there is a fixed rate of BTUs (Min Fire) that will be
removed (PID discontinuity to modulate from Min Fire to 0
BTUs on a boiler). The timer allows for this loss of BTUs.
This cycle will continue until the call for heat is satisfied or
the Warm Weather Shutdown feature is enabled.
Mixed Boiler Types Using
Priority Sets
Using the Basic Multi Boiler System Operation, a MIXED
boiler Priority method may be added to control condensing,
non-condensing, base load, or other boiler SETs in a system
together. These sets compose a system which provides for
optimal performance and economy. Having dedicated sets
of boilers gives the system engineer a tool to create many
different boiler systems.
A boiler set can be constructed by simply setting the firing
Priority on each boiler (to be in a set) at the same priority.
Setting all (example) condensing boilers to the highest
Priority of 1, and then setting all (example) non-condensing
boilers to a Priority of 2, will create (2) sets of boilers, one
condensing and the other non-condensing. Once this is
done, the Priority 1 set of condensing boilers will have a
firing order that has a higher Priority and is independent of
the other non-condensing set with the lower priority. The
boiler set with the highest Priority can then be fired based
on a conditional settings menu. The lower Priority set will
follow. If the priority set is used with condensing and non-
condensing boilers a boiler may also go offline when a
return temperature is too low.
Boilers will be staged on and off using the ADD and SHED
timers as always, but the boilers can now be grouped.
Mixed Boiler System Operation
Starting Boilers:
When a boiler is to be fired (water temp is below the heating
band), the Master checks the HeatNet boilers it has
available. The Master boiler then looks at which boilers are
returning Priority firing status (set on a boiler in:
(ADVANCED SETUP: SYSTEM: BOILER TYPE:
PRIORITY: 1). If the Start condition for the Priority 1set is
met (ADVANCED SETUP: FIRING MODE: MODE:
MIXED: SET FIRST (example), the Master or Member
boiler that is configured as PRIORITY 1, with the lowest
runtime, will be fired FIRST (example).
As long as the start condition for Priority 1 is met, all
boilers in the PRIORITY 1 set will fire based on runtime.
Once all boilers in the PRIORITY 1 set have fired, the
PRIORITY 2 set of boilers will fire based on runtime.
If the Start condition changes and/or is not met (such as
with: OA T or RET temp), the PRIORITY 2 set of boilers
will fire first/next based on runtime. This has the effect of
flipping the Priority of the sets.
Stopping Boilers:
When a boiler is to be stopped (water temp is above the
heating band), the Master checks the HeatNet boilers it has

SETUP & OPERATION HeatNet Control V3
Page 13
available. The Master boiler then looks at which boilers are
returning Priority firing status (set on a boiler in:
(ADVANCED SETUP:FIRING MODE: MODE:
MIXED: SET LAST (example) If the Stop condition for
Priority 1 is met, the Master or Member boiler that is
configured as PRIORITY 1 with the highest runtime will be
stopped LAST (example). As long as the stop condition and
SHED DELAY time are met, all remaining PRIORITY 1 set
of boilers will stop based on runtime. If the Stop condition
changes and/or is not met (such as with: OAT or RET
Temp), the PRIORITY 2 set of boilers will stop first/next
based on their highest runtime.
A boiler’s firing Priority can be designated as such in:
ADVANCED SETUP: SYSTEM: BOILER TYPE:
FIRING PRIORITY: 1 menu on each boiler. A Priority of
‘1’ is the highest priority, a ‘2 the lowest (default is always
2).
Figure 3 Mixed Boilers: Example: Condensing/Non-Condensing
In the example Mixed Boilers: Condensing/Non-
Condensing, condensing boilers and non-condensing boilers
are used, but other combinations may also be used. Another
example could use (2) small boilers and set them to
Priority 1 and then use (3) larger boilers and set them to
Priority 2. Using these Priority settings (with the conditions
menu), the small boilers can run first during the shoulder
months (Spring and Fall) and the larger boilers can fire last
during the colder Winter season (base loading set).
Before the MIXED method can be used, the firing mode on
the Master boiler must be set to MIXED. ADVANCED
SETUP: FIRING MODE: MODE: MIXED. Pressing the
SELECT key when the cursor is pointing to MIXED will
enter the conditions menu. The START and STOP
conditions for starting and stopping the Priority boiler set
may be configured here. Temperatures are adjustable.
Once the conditions menu has been entered, the firing order
and stop order of the Priority 1 boiler set can be selected
based on up to (3) conditions in the conditional settings
menu. All conditional settings apply to the Priority 1 boiler
set. When the conditional settings do not apply to the
Priority 1 set, the conditional settings will apply to the
Priority 2 boiler set.
START P R I O R I T Y 1
>SET : FIRST
STOP P R I O R I T Y 1
SET : OAT < 15°F

SETUP & OPERATON HeatNet Control V3
Page 14
Start/Stop Priority Conditions
The following is an example using mixed
condensing and non-condensing boilers:
FIRE FIRST
Condensing boilers may be configured to fire first (set to
PRIORITY 1) when:
2. The Return water temperature is below 140F and
condensing occurs. (The Master’s return water sensor
would need to be moved to the header return.)
3. The Outside Air Temperature is above a setpoint
determined by the system configuration. This setpoint
ensures that the more efficient condensing boilers run
first during shoulder months (Spring and Fall) when
minimal heating is required. Below this setpoint, larger
boilers should be brought on first to “base load” the
system.
4. Greater efficiency is required.
STOP FIRST
Condensing boilers may be configured to stop first (set to
PRIORITY 1) when:
The Return water temperature is above 140F and
condensing is minimized, thus leaving the larger lower cost
boilers running to carry the load.
1. The Outside Air Temperature is below an adjustable
setpoint determined by the system configuration. This
setpoint ensures that the larger non-condensing boilers
run during the coldest months when maximum heating
is required. Above this setpoint smaller condensing
boilers should be brought on first to run the system as
efficiently as possible.
2. Maximum heating is required
START PRIORITY 1 SET
Selections (always the lowest runtime first):
The condensing boiler set (Priority 1) has a
higher Priority to fire when one of these
conditions is met. Values are adjustable.
FIRST: The condensing boilers (Priority 1) are always
started FIRST
OA T > 15F: The condensing boilers (Priority 1) are
started when the OA temperature is greater than the Mixed
Boiler Outdoor Air Temperature setting.
RET < 140F: The condensing boilers (Priority 1) are
started when the Return water temperature is less than the
Mixed Boiler Return temperature setting (This may not
applicable in most configurations since the local return
temperature on the Master is used to provide a difference
temperature across the heat exchanger. A System Return
sensor will be required. However, the return temperature
sensor may have been moved on the Master to provide
system return temperature on existing installations and is
still supported).
STOP PRIORITY 1 SET
Selections (always the highest runtime first):
The condensing boiler set (Priority 1) has a
higher Priority to stop when one of these
conditions are met. Values are adjustable.
LAST: The condensing boilers (Priority 1) are always
stopped LAST.
OA T < 15F: The condensing boilers (Priority 1) are
stopped first when the OA temperature is less than Mixed
Boiler Outdoor Air Temperature.
RET > 140F: The condensing boilers (Priority 1) are
stopped first when the Return water temperature is greater
than the Mixed Boiler Return temperature. (This may not
applicable in most configurations since the local return
temperature on the Master is used to provide a difference
temperature across the heat exchanger A System Return
sensor will be required. However, the return temperature
sensor may have been moved on the Master to provide
system return temperature on existing installations and is
still supported).
Start/stop settings
Any combination of Start Conditions and Stop Conditions
can be used to optimize the mixing of condensing
(Priority 1) and non-condensing boilers (Priority 2) for best
performance/economy.
The default settings for the start and stop conditions of the
condensing set are:
The default start setting always starts the condensing boilers
(Priority 1 example) first, except for the lead boiler setting.
The lead boiler will always start first if enabled, unless
there is a boiler already running (this includes a Member
boiler in LOCAL). The default stop condition setting always
stops the condensing boilers (Priority 1) last.
If prolonging the life of the heat exchanger(s) on non-
condensing boilers is very important, consider starting the
START P R I O R I T Y 1
>SET : FIRST
STOP P R I O R I T Y 1
SET : L A S T

SETUP & OPERATON HeatNet Control V3
Page 15
condensing boilers (Fusion-Series) when the return water
temperature is below 140F.
The return water temperature sensor would
need to be moved from the Master’s return
inlet to the system return. The EXCHGR
DELTA may need to be adjusted in SETUP:
AUX FUNCTIONS: HEAT EXCHANGER
to prevent the Master from going to ½ input
when a high DELTA T is reached.
This method would lead to the non-condensing boilers
carrying the load when the system temperature stabilizes
above 140F, since non-condensing boilers will start first
with the Return water temperature is > 140F. The
condensing boilers can then be stopped first when the RET
water temperature is above the 140F. Remember, any
combination of the Start and Stop conditions may be applied
for best performance and economy in the system. Also, non-
condensing boilers may be set to go offline when a return
temperature is too low using the SETUP: AUX
FUNCTIONS: HET EXCHANGER: TEMP DISAB menu.
Base load boilers can also be mixed in the same way as
condensing and non-condensing boilers. The base load
boiler(s) can be prioritized in one set (example, Priority 2)
and non-base load boilers (Priority 1). The non-base load
boilers can then be set to fire first and once they are all
firing, the base load boiler would fire.
To minimize the cycling of a large base load boiler, consider
using the stop condition. Change it to the OAT < 15F
(Outside Air Temperature) condition. This setting may be
used to stop the Priority 1 boiler set when the OAT drops
below the OAT setpoint, thus leaving the large base loaded
boiler on and shutting off the condensing boilers first. This
is also true when using the OAT setting to start the
Priority 1 boiler set when the OAT is above the start
setpoint. To use temperatures as start and stop conditions,
the system design temperatures must be known.
Selecting Mixed Boilers
There are a few factors to consider when choosing which
type of boilers to use in a mixed system. These factors need
to be considered when boilers are added or shed. When
BTUs are introduced into the system by adding boilers, the
amount of introduced BTUs should be smooth (linear). If
these factors are not considered, discontinuity in BTUs may
occur when boilers are added and as a result, short cycling
will occur.
1. Turndown: This is the ratio of minimum fire rate to
maximum fire rate: Example: a 20% minimum
modulation = 5:1 turndown (100%mod / 20% mod). A
(1) million BTU boiler = 200,000 BTUs minimum
input.
2. MOD MAX CLAMP: This value determines the
maximum modulation % at which the boilers will fire
to, until all available boilers are firing.
3. Total System BTUs.
4. Desired Effective Turndown. This is the lowest
firing rate of the system relative to the maximum firing
rate of the system. The larger the value, the lower the
BTUs that can be delivered to a light load.
5. Piping.
Mixed System Type 1:
High System Turndown
The following examples are of mixed boiler systems with
high effective system turndown and fault tolerance built in.
When boiler types are the same, the system turndown is
limited to the boiler’s min input and fault tolerance is
always present. When the system has mixed boiler types,
consideration needs to be taken on what types can be mixed
properly to achieve a high system turndown and provide
some fault tolerance.
Fault tolerance allows for one boiler in the Priority 1 system
to fail and any boiler(s) in the Priority 2 system to fail and
still provide near linear (continuity) BTU response when
adding boilers. This is illustrated in the following examples
using the Boiler System Response graphs.
The Futera III/Fusion-Series Mixed Boiler System
(examples) is advantageous in providing low BTU input for
light loads and high BTUs for heavy loads. The effective
system turndown minimizes short cycling when light loads
are present by assigning smaller boilers to Priority 1,
running them first, and then stopping them last.
In order to achieve the high effective
turndown, smaller boilers are required
(plumbing considerations need to be
considered here due to differing flow/volume
characteristics through the large and small
boilers).
Example Systems:
Figure 4 Non-Mixed Boiler System
System
MMBTU
Effective
Turndown
MOD
MAX
MB/MW 4:1
10.0
20:1
70%
2000, 2000, 2000,
2000, 2000
5.0
20:1
70%
1000, 1000, 1000,
1000, 1000
2.5
20:1
70%
500, 500, 500, 500,
500

SETUP & OPERATON HeatNet Control V3
Page 16
With the traditional Non-Mixed boiler system, the effective
turndown increases by the turndown ratio for every boiler
added. The min fire rate is equal to the minimum BTUs that
can be delivered to the system.
Number of boilers * Turndown Ratio = Effective System
Turndown: 5 * 4:1 = 20:1.
Figure 5 Mixed Boiler System
System
MMBTU
Effective
Turndown
MOD
MAX
Priority 1
MB/MW
4:1
Priority 2
MB/MW
4:1
4.5
24:1
46%
750, 750
1000, 1000,
1000
4.75
32:1
60%
500, 500
1250, 1250,
1250
6.5
26:1
45%
1000, 1000
1500, 1500,
1500
6.0
48:1
55%
500, 500,
500
1500, 1500,
1500
With the mixed boiler system, a lower minimum fire
rate/BTU can be delivered to the system by using small
boilers with larger boilers. This works in much the same
way as base loading.
Figure 6 Futera III/Fusion Boiler Btu Chart (MBH)
MB/MW
CB/CW
500
750
1000
1250
1500
1750
2000
Max Input
500
750
1000
1250
1500
1750
2000
Min Input
4:1
125
188
250
312
375
437
500
Mod Max
80%
400
600
800
1000
1200
1400
1600
Mod Max
70%
350
525
700
875
1.05
1220
1400
Mod Max
60%
300
450
600
750
900
1050
1200
Mod Max
50%
250
375
500
625
750
875
1000
When selecting the Priority 1 boiler(s) for a high effective
system turndown, the BTU Min Input is selected first. (See:
Futera III/Fusion Boiler Btu Chart). Next, the MOD-MAX
value of this Priority 1 boiler needs to be greater than: Mod
MAX % =
(Priority 1 ‘s Min Input + Priority 2 ‘s Min Input)
Max Input of the Priority 1 boiler
The reason for this is to keep the continuity of BTUs linear
without a BTU bump (discontinuity) when boilers are added
or shed. This is illustrated in the Boiler System Response 2
graph.
If redundancy is not required, the min inputs of the
Priority 1 boilers may be summed to lower the Mod Max %
value so smaller Priority 1 boilers can be used. The sum of
the min inputs would then need to be divided by the sum of
the Max Input of the Priority 1 boilers. The effect of this
would create a higher turndown. See: EXCEPTION NOTES:
Mod MAX % =
(((Priority 1 Min) * (#Priority 1’s)) + Priority 2 Min)
Max Input of Priority 1 boiler * (#Priority 1’s)
Example: (2) CB/CW500, (2) MB/MW1250
Redundancy: (125 + 312) / 500 = 88%
No Redundancy: (125 * 2) + 312) / (500 * 2) = 56%
EXCEPTION NOTES:
1. Mixing more than two different size/type boilers
becomes more complex than the scope of this manual
and is not recommended.
2. If using more than one Priority 1 boiler and the
calculated value is <
Priority 1Min * 2
Priority 1 Max Input
Use this result PLUS note 3 value as the
ModMax%.
3. Always add a few % (3-5%) to the calculated MOD
MAX % value to allow a guard band (tolerance).
4. If boilers are of different sizes, try to use larger Priority
2 boilers.
If the calculated Mod MAX % value is greater
than 99%, the combination cannot be used
since short cycling will occur.
Once the Priority 1 and Priority 2 boilers are selected, they
can be multiplied in each Priority set to achieve the desired
system design BTUs. If the # of boilers becomes a large
number, a Priority 1 boiler with a higher Min Input may
need to be selected.
While considering the MOD-MAX value, the lower the
MOD-MAX the greater the combustion efficiency since it
effectively limits the input rate. The Typical Efficiency of

SETUP & OPERATON HeatNet Control V3
Page 17
Non-Condensing Boilers chart can help illustrate how the
MOD-MAX value can affect the efficiency by limiting the
input until all boilers have fired. Non-condensing boiler
efficiency is relatively flat compared with condensing as
illustrated in the Typical Efficiency of Condensing Boiler
graph.
Figure 7 Typical Efficiency of Non-Condensing Boilers
Figure 8 Typical efficiency of condensing boilers
(GAMA BTS2000 method)
In the Mixed Boiler System table line 2 example, (2)
MB/MW 500s are set as Priority 1 and MB/MW 1250s set
as Priority 2. With a MOD MAX of 60%, each 500 can run
to 300M (600M total) before a 1250 is called ON (Add
Delay timer). Once both 500s are running and the 1250 is
called on, all (3) boilers will drop to a total of the 600M
BTUs: The sum of the 500, 500, and 1250 would equal
about 27% modulation: (.27 * 500M) + (.27 * 500M) + (.27
* 1.25MM) or: 135M +135M + 337M = 607M and operate
at higher combustion efficiencies (noncondensing boilers
have minimal effect individually, but can have an effect if
many are used).
If CB/CW Fusion boilers are substituted for the MB/MW
Futera III boilers, the efficiency is greatly increased due to
the condensing mode of these boilers. When using CB/CW
Fusion boilers, during the first 2850 MBTH of load, the
combustion efficiency is maximized by running the CB/CW
Fusion boilers from low to middle input rates. See: Typical
Efficiency of Condensing Boiler graph.
Figure 9 Boiler System Response 1
(2) MB/MW 500s, (3) MB/MW 1250s
When running non condensing boilers at low
input rates, the risk of condensing should be
considered.
The Boiler System Response 1 chart illustrates how each
boiler (in the example) is brought on and fires to 60%, drops
to a lower fire rate and then adds the next boiler (vertical
dashed lines). Once all boilers are firing, the modulation is
released allowing all boilers to fire to 100%.
Now, if (1) MB/MW 500 (one of the MB/MW 500s was
brought offline) were used with (3) MB/MW 1250s and the
Mod-Max is set to 60%, the MB/MW 500 would fire to 300
MBTUs and wait for the MB/MW 1250 (Boiler System
Response 2 graph). Now, the minimum input rate would be
312M (MB/MW 1250) + the 125M (MB/MW 500) (already
running, but dropped to low fire when the MB/MW 1250
fired), the total being 437M. With a 60% MOD-MAX
clamp, there would be 137 MBTUS more than needed and
added to the system when the MB/MW 1250 fired.
The PID algorithm would then compensate for the
discontinuity (bump) in BTUs and the MB/MW 1250 could
shut off (short cycle).
This discontinuity is observed in the graph below, (Boiler
System Response 2) where the jump from the MB/MW 500
@60% to the firing of the MB/MW 1250 is apparent.
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0 1,000,000 2,000,000 3,000,000 4,000,000 5,000,000
Input, %
System Load, Btu/Hr
Blr 1+2+3 (2250 MBTU)
Blr 1+2+3+4 (3500 MBTU)
Blr 1+2+3+4+5 (4750 MBTU)

SETUP & OPERATON HeatNet Control V3
Page 18
Figure 10 Boiler System Response 2
(1) MB/MW 500, (3) MB/MW 1250, 60% Mod-
Max
To correct this would require the MB/MW 500 to set the
MOD-MAX to roughly 90% (Boiler System Response 3: not
as efficient as it could be when using CB/CW Fusion
boilers) in order to have a linear BTU transfer when the
MB/MW 1250 is added (fired).
Figure 11 Boiler System Response 3
(1) MB/MW 500, (3) MB/MW 1250, 90% Mod-
Max
An MB/MW 500 running with a MB/MW 1250 may not be
an optimal choice unless (2) MB/MW 500s are used in the
Priority 1 set or (3) MB/MW 500s and one is allowed to be
taken offline.
A system employing this redundancy where (1) is allowed
to be taken offline is listed in the MIXED BOILER SYSTEM
chart. This system uses (3) MB/MW 500s and (3) MB/MW
1500s. Two of the MB/MW 500s are treated as one when
adding the min inputs of the Priority 1 set.
Figure 12 Boiler System Response 4
(2) MB/MW 500s, (3) MB/MW 2000s
The Boiler System Response 4 graph illustrates another
system where 80% is used as the MOD-MAX clamp. With
this example, when using all non-condensing boilers, the
system can maximize the use of the smaller boilers before
calling the larger ones.
In summary, the system should be tuned using the boiler
selection charts and the MOD-MAX value. Since selecting
the Priority 1 boiler is integral to the fault tolerance of the
system, it is important to note any discontinuities in BTUs if
a Priority 1 boiler fails when multiple Priority 1 boilers are
used.
Mixed System Type 2:
Condensing / Non-Condensing
This mixed system may also have mixed boilers with
differing sizes as outlined in the Mixed System Type 1:
High System Turndown section. In the following examples
condensing high mass boilers will be used with non-
condensing low mass boilers. The reason for creating a
mixed system is primarily to control the system cost.
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0 1,000,000 2,000,000 3,000,000 4,000,000 5,000,000
Input, %
System Load, Btu/Hr
Blr 1+2 (1750 MBTU)
Blr 1+2+3 (4250 MBTU)
Blr 1+2+3 (3000 MBTU)
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0 1,000,000 2,000,000 3,000,000 4,000,000 5,000,000
Input, %
System Load, Btu/Hr
Blr 1+2 (1750 MBTU)
Blr 1+2+3 (4250 MBTU)
Blr 1+2+3 (3000 MBTU)
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0 1,000,000 2,000,000 3,000,000 4,000,000 5,000,000
Input, %
System Load, Btu/Hr
Blr 1+2+3 (3000 MBTU)Blr 1+2+3+4 (5000 MBTU)
Blr 1+2+3+4+5 (7000 MBTU)

SETUP & OPERATON HeatNet Control V3
Page 19
Figure 13 Mixed Condensing/Non-Condensing Boiler
System
Local Pump
Local Pump
MASTER
Condensing
MEMBER 1
Condensing
HNETHNET
Header Sensor
System Return Sensor
HNET
Local Pump
Local Pump
System Pump
MEMBER 2
Non-
Condensing
MEMBER 3
Non-
Condensing
Priority 1 Set Priority 2 Set
M
Combustion Air Damper
Outdoor Air Sensor
Outdoor Air
Sensor
Figure 14 Mixed Boiler System
System
MMBTU
Effective
Turndown
MOD
MAX
Priority 1
CB/CW 4:1
Priority 2
MB/MW
4:1
4.5
24:1
60%
750, 750
1000, 1000,
1000
4.75
32:1
60%
500, 500
1250, 1250,
1250
6.5
26:1
65%
1000, 1000
1500, 1500,
1500
6.0
48:1
65%
500, 500,
500
1500, 1500,
1500
For the examples, the RBI FIII/Fusion series water heaters
will be used. These boilers are non-Condensing, fully
modulating, low mass, and HeatNet compatible.
The Mixed Boiler System table show some examples of
mixed systems using different sizes along with Fusion
condensing (Priority 1) and Futera III non condensing
(Priority 2) boilers.
Using the boiler charts and the examples used in: Mixed
System Type 1: High System Turndown, a mixed boiler
system can be designed. The Priority 1 boilers should be
setup so as to keep the non-condensing boilers from seeing
return water temperatures of less than 140F to ensure a long
heat exchanger life.
Normally, the Priority 1 boilers will fire first. Once all the
Priority 1 boilers are firing, the next boiler to fire (after the
ADD BOILER timer expires) would be the Priority 2 (non-
condensing). If the return water temperature has not come
up to ~140F, the non-condensing boilers could fire in a
condensing mode. The ADD BOILER delay timer would
have to be set to a long enough period to ensure this does
not happen. Even then, the load may be too great. The
following note will explain an alternative way (not
depending on the ADD BOILER DELAY) to keep non-
condensing boilers from firing in a condensing mode.
When running with a remote BMS setpoint, care must be
taken that an Outside Air reset setpoint (or other setpoint)
sent by the BMS is not set too low. If the BMS system is
controlling the setpoint close to the condensing temperature,
the return water temperature may never rise sufficiently to
keep boilers out of a condensing mode. HeatNet online is a
good way to monitor this scenario if suspected.
If the firmware version for a HeatNet V2
board is at least 3.47(or a version 3
board), the non-condensing boiler may hold itself off from
being added to the HeatNet Master’s available to fire list.
This would effectively keep the non-condensing boiler
from firing in a condensing mode, but as a result, may not
satisfy the system setpoint.
In order to use this feature, the version 2 board would
need to monitor the system or local return temperature.
This can be done locally by setting SETUP: AUX
FUNCTIONS: HEAT EXCHNAGER: TEMP DISAB:
RETURN if the there is no pump/valve limiting flow
continuously through the boiler. If there is a pump/valve
limiting the flow through the boiler, the SETUP: AUX
FUNCTIONS: HEAT EXCHNAGER: TEMP DISAB: SYS
RET needs to be set. Then the Master boiler needs to set
SETUP: AUX FUNTIONS: HEAT EXCHNAGER: SEND
RETURN: to which of its return temperatures it would
send to all boilers. These include the Local Return
temperature or the System Return temperature.
The Member’s menu “SETUP: AUX FUNCTIONS: HEAT
EXCHNAGER: TEMP DISAB:”if set to RETURN or SYS
RET, will force the boiler to become unavailable to
HeatNet when the SETUP: AUX FUNCTIONS: HEAT
EXCHNAGER: TEMP< 140F. This value is adjustable to
135F if a forced air fan is used. When the SYS RET or
RETURN temperature is <140F the boiler responds to a
HeatNet Master’s request as”unavailable”. As soon as
the return temperature reaches 140F, the boiler will
respond to the Master’s request that it is available to fire.
If the Master boiler is a version 2 board, the Master will
always transmit its Local Return temperature to all
boilers. If the Master is set to Priority 1 and all other
non-condensing boilers are set to Priority 2, the Master
should always remain on if there is a call for heat. This
requires that the Priority 1 boiler be set up to start first
and stop last. Using this method should always send a
valid return temperature to the Member boilers. This
method can also be used with a version 3 board, but a
system return sensor is preferred.
When this condition is in effect, the STATUS * screen will
indicate “blr offline”. While the boiler is in this “not

SETUP & OPERATON HeatNet Control V3
Page 20
available” state, it can still be fired locally and failsafe is
still available.
SETUP: AUX FUNCTIONS: HEAT EXCHANGER:
SEND RETURN:
OFF The Master sends its return
temperature to all boilers
RETURN The Master sends its return
temperature to all boilers
SYS RET The Master sends the system
return temperature to all boilers
SETUP: AUX FUNCTIONS: HEAT EXCHANGER:
LOW TEMP:
OFF No check is made to the return
temperature –boiler remains
online
RETURN Uses the boilers own return
sensor (No pump /valve present)
SYS RETURN Uses the System Return temp
received from the Master Boiler
(its Local or System Return).
SETUP: AUX FUNCTIONS: HEAT EXCHANGER:
TEMP < 140F
Adjustable threshold temperature below which the
boiler will take itself offline.
1 degree F of hysteresis is provided so as to not
toggle offline<-to->online at the threshold temp.
Since the FIII boiler is non-condensing, the efficiency vs.
input is relatively flat. The MOD MAX value will not have
the same impact if the FIII non-condensing boilers were
placed in the Priority 1 set.
Futera III/ Fusion Boiler BTU Chart
In the Mixed Boiler System table (Figure 15) line 2
example, (2) CB/CW 500s are set as Priority 1 and (3)
MB/MW 1250s set as Priority 2. With a MOD MAX of
60%, each 500 can run to 300M (600M total) before a 1250
is called ON (Add Delay timer). Once both 500s are running
and the 1250 is called on and running, all (3) boilers will
drop to a total of the 600M BTUs: The sum of the 500, 500,
and 1250 would equal about 27% modulation: (.27 * 500M)
+ (.27 * 500M) + (.27 * 1.25MM) or: 135M +135M + 337M
= 607M and operate at higher combustion efficiencies: 27%
is roughly between the top two lines on the Typical
Efficiency of Condensing Boilers chart.
The Boiler System Response 5 chart illustrates how each
boiler (in the example) is brought on and fires to 60%, drops
to a lower fire rate and then adds the next boiler (vertical
dashed lines). Once all boilers are firing, the modulation is
released allowing all boilers to fire to 100%.
Figure 15 Boiler System Response 5
(2) CB/CW 500s, (3) MB/MW 1250s
So, for the first 600 MBTH of load, the combustion
efficiency is maximized by running the (2) fusion boilers
from low to middle input rates. Running the (2) fusion
boilers first also has the added effect of minimizing the
return water temperatures of <140F from reaching the
noncondensing boilers.
Figure 16 Futera III/Fusion Boiler Btu Chart (MBH)
MB/MW
CB/CW
500
750
1000
1250
1500
1750
2000
Max Input
500
750
1000
1250
1500
1750
2000
Min Input
4:1
125
188
250
312
375
437
500
Mod Max
80%
400
600
800
1000
1200
1400
1600
Mod Max
70%
350
525
700
875
1.05
1220
1400
Mod Max
60%
300
450
600
750
900
1050
1200
Mod Max
50%
250
375
500
625
750
875
1000
In summary, the system should be tuned using the boiler
selection charts and the MOD-MAX value so that boilers
are brought on and fired in their respective efficiency curve
while maintaining continuity in BTUs. Since selecting the
Priority 1 boiler is integral to the fault/offline tolerance of
the system, it is important to note any discontinuities in
BTUs if a Priority 1 boiler goes offline when multiple
Priority 1 boilers are used.
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0 1,000,000 2,000,000 3,000,000 4,000,000 5,000,000
Input, %
System Load, Btu/Hr
Blr 1+2+3 (2250 MBTU)
Blr 1+2+3+4 (3500 MBTU)
Blr 1+2+3+4+5 (4750 MBTU)