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Keystone KS/KW

High Efficiency Condensing Boilers from 399 to 850 MBH

Keystone Condensing Boilers provide powerful solutions for large residential and light commercial applications with 5 models with inputs from 399 to 850 MBH. These products feature a stainless steel heat exchanger with a thermal efficiency between 95 and 97%. Their compact design minimizes floor space while the cabinet provides easy access to all components. The large user friendly control interface makes set-up easy. The advanced control modulates the boiler with a 5 to 1 turndown ratio. Up to 8 boilers can be joined in a cascade while the control features parallel modulation and boiler rotation to maximize efficiency and service life.

Keystone Condensing Boilers from 500 to 850 MBH are CSD-1 compliant as a standard feature. This saves both cost and installation time


  • Energy efficient with 95% to 97% Thermal Efficiency
  • Stainless Steel Heat Exchanger
  • CSD-1 Standard on 500 to 850 MBH Boilers
  • Integrated Cascade
  • Multiple pump control and thermostat inputs
  • 5 to 1 Turndown
  • 75 psi Pressure Relief Valve on Keystone Boilers



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