Raytherm® Low NOx Hydronic Boiler, 181-261

Model Number Full Input in
 Flue Dia.
H-181 181,000

Available Firing Modes
H3 2-Stage
H4 On-off
 *H3-401 (2-Stage) has input 375,000 BTUH


  • Cast-iron Headers with Copper Finned Tube Heat Exchanger.
    Single bank, straight through design delivers lowest pressure drop. Integral fins have ten times the heat transfer surface of plain tubes
  • 82% efficiency, CAT I venting
  • Corrosion Resistant Steel
    Fittings are brush galvanized against rust. Heat shields are corrosion-resistant steel. Jacket has Polytuf powder coat finish
  • 24-Volt Controls
    Are totally enclosed for protection. Door is easily removed for inspection and service
  • Floating Return Header
    Immunizes heat exchanger to thermal shock
  • Tube Sheet and “O” Ring Construction
    Eliminates the repair and maintenance problems associated with rolling tubes directly into a casting
  • Electronic Controller with outdoor reset varies the setpoint as the air temperature changes.
  • Interlocking Refractory Panels
    Sealed corners reduce radiation losses
  • NOx emissions under 55 PPM (40ng/j). Consult local emissions requirements prior to ordering.
  • Stainless Steel Burners
    Maintain precise combustion at all firing rates, burn quietly and won’t clog or corrode
  • Slide-out Burner Tray
    Allows easy inspection and service
  • Spark-to-Pilot Ignition
    The most dependable ignition method available
  • Available for Natural Gas Only.