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Product Spotlight



FlexCore Symmetrical Firetube boilres bring hydronic heating products to unprecedented levels of operating efficiency.


FlexCore was designed, developed, and engineered by the experts at RBI.


Engineered for performance and longevity, 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.


All “firetube” boilers are designed to do the same thing: Heat water in an efficient manner.


That is where the comparison ends!


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.


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.




  • Sizes from 850 MBH to 6,000 MBH
  • 96.8% AHRI Certified
  • Up to 99% maximum efficiency
  • Primary/Secondary, Full Flow, and Variable Flow systems
  • Superior durability
  • Easy installation & maintenance
  • Versatile footprint fits through 36" door (all size models)
  • PVC & Polupropylene (PP) vent


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Product Spotlight