FLX Watertube Boiler

Packaged Watertube Boilers

  • Boiler Horsepower: 36 - 600
  • Input Capacity (MBH): 1,500 - 25,000
  • Steam or Hot Water: Both
  • Vessel Design: Watertube
  • Number of Passes: 5
  • Fuel: Natural Gas, #2 Oil, Propane, Digester Gas, Combination Firing
  • Emissions (ppm NOx): Standard, <30, <20, <9
  • Steam or Hot Water
  • 1,500-25,000 MBH Input
  • Natural Gas, #2 Light Oil, Propane, Digester Gas
  • 15-250 psig Design Pressure
  • Available to <9 ppm NOx
  • Field Erectable


The FLX is a UL listed packaged boiler that is versatile and can handle both commercial and Industrial applications. The compact 5-pass bent water-tube design provides efficiency ratings up to 81% (Steam) and 85% (Hot water).


The FLX's burner can burn non-standard and renewable fuels and features a fully modulating burner to ensure optimum efficiency throughout the firing range. It can also help meet emissions reduction goals, down to <9 ppm NOx with low CO.


  • Product Overview
  • Related Resources
  • Applications
  • Up to 15:1 turndown (Standard emissions) and 10:1 (Controlled emissions)
  • Rapid response to swinging loads
  • Small footprint, field erectable
  • Thermal shock resistance, 25-year limited pressure vessel warranty
  • Reliable burner, 10-year limited burner warranty
  • Easy burner and pressure vessel access for service and maintenance


The FLX boiler package includes a burner, trim, and control system for a completely integrated and engineered solution from a single source. Each boiler design was witness tested by a third party in Cleaver-Brooks state of the are boiler laboratory to ensure maximum reliability.

FLX has distinct design features that include non-welded ferrule tubes for ease of tube replacement; removable sectioned side panels permit full access to all tubes. FLX boilers are a 5-pass cross flow water tube design, optimized through computational fluid dynamics to maximize heat transfer thru every pass. Unlike competing designs, FLX features a water-cooled furnace and fireside passes that do not require baffles, which lowers refractory maintenance costs throughout the boiler’s life and reduces the total cost of ownership.

FLX field erectable option allows for boiler replacement in tough-to-access spaces. The pressure vessel is assembled at the factory and hydro-tested before shipment. During the disassembly, the tubes are matched marked for easy installation on site.


Steam Applications, Terminology and How to Achieve Best Results →

Learn how the industry defines steam from utility, saturated and superheated to filtered and clean. Applications for the various steam types will be covered along with operation best practices.

Boiler Room Installation Considerations for Safety, Reliability, and Efficiency →

There are several factors that are important to consider when installing either a steam or hydronic boiler system in order to maximize safety, reliability and efficiency. Learn about the several aspects that help to ensure proper boiler installation.

FLX Packaged Boiler Video →

  • Process Steam
  • Industrial Process
  • Building Heat
  • Sterilization
  • Healthcare