Flexcore
Heat Exchanger | Stainless Steel Firetube Heat Exchanger |
---|---|
Size Range | 850 - 6,000 MBH |
AHRI Boiler Efficiency | 96.8%* |
Turndown | Up to 10:1* |
Application | Variable Volume, Full Flow, Primary / Secondary |
FlexCore Symmetrical Firetube boilers bring hydronic heating products to unprecedented levels of operating efficiency.
Unlike other manufacturers; from start to finish the FlexCore was designed, developed and engineered by the experts at RBI.
Engineered for performance and longevity the FlexCore utilizes a perfectly temperature balanced heat exchanger that provides not only the highest efficiencies but also a durability beyond that of any competitive firetube boiler on the market.
*Efficiencies and turndown vary by size

Features and Benefits
- 850 - 6,000 MBH
- 96.8% AHRI Certified Efficiency*
- Full Modulation (up to 10:1*)
- O2 Monitoring
- 304L Stainless Steel Firetube Heat Exchanger
- Variable Volume, Full Flow and Primary/Secondary
- Patented "Turbo Pilot" Sure-fire Ignition
- Sika Vortex Flow Sensor
- HEATNET 3.0 Integrated Control Platform
- Touchscreen Programming & Diagnostics
- Modbus, LonWorks and BACnet BMS Integration
- Symmetrically Air/Fuel Coupled
- Category II and IV (up to 160’)
- PVC/CPVC, Polypropylene and Stainless Steel Vent Approved
- Warranty (Heat Exchanger): 10-years
- Superior Durability
- Easy Installation & Maintenance
- Fits through 36" Door
- Low Nox
*Efficiencies and turndown vary by size
Have Questions?
Heat Exchanger
Symmetrical Firetube
All "firetube" boilers are designed to do the same thing: Heat water in an efficient manner.That is where the comparison ends!
The RBI difference...
FlexCore Symmetrical Firetube boilers are designed for the long haul with no tradeoffs in efficiencies. In order to operate at premium condensing efficiencies many factors come into play that can affect the design, performance and, as importantly, the durability.
FlexCore is engineered to provide perfect temperature symmetry around an ultra-high efficient core. Flue gas temperatures are even and a consistent temperature rise across all the tubes results in a unrivaled<5° temperature difference across the heat exchanger with NO intra-tubular stresses as seen in many of today’s competitive designs.
RBI “flexes” its strength by design. At its core is a piston-like heat exchanger engineered to eliminate the expansion and contraction stresses seen in today’s boilers by creating a temperature balanced symmetrical upper tube sheet reminiscent of a diaphragm that absorbs the stresses from this piston-like motion at any water temperature delta.
Condensate is removed through FlexCore’s linear design resulting in ultra-high efficiencies in a compact design with minimal corrosive effects.
FlexCore scrubs every last bit of heat from the combustion gases keeping stresses low and efficiencies high at all modulation rates, making FlexCore the most efficient boiler on the market today.

Gas Train
HEATNET 3.0
Digital Touch Screen Programming
Lead/Lag Cascade (16 Units)
Mixed-Size Unit Communication
Adaptive Modulation
Circular Pump/VFD/Valve Control
BMS Integration
Freeze Protection & Delta T Monitoring
Hybrid/base Load Capability
Priority Boiler Control
Domestic Hot Water Communication
Web-Based Remote Monitoring/Dashboard
Diagnostics and Troubleshooting
Set Points
Exclusive Remote Monitoring Capability with HEATNET Online
Ease of Service
FlexCore units operate safely and efficiently at all times by reacting to changes in the air or fuel flow which can compromise combustion. Air/Fuel coupling automatically adjusts to any changes in the environment by reducing input levels to maintain optimum combustion quality while providing the highest degree of safety. Air/Fuel coupling further increases application flexibility by allowing installation of FlexCore units in areas of variable air inlet and gas pressures without compromising safety or performance. Space-saving Footprint Advanced gas train design monitors and regulates gas input based on combustion air pressure, which in turn provides highly repeatable air/fuel ratio throughout the operating range.
Ratings and Dimensions
