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What is the optimum tempreture setting for a cast iron boiler

Jimbo_5 Member Posts: 218
Its a WMc (CGa) in a one story house with a copper fintube loop. Just curious.


  • Jamie Hall
    Jamie Hall Member Posts: 23,446
    Return temperature not less than 160.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    HVACNUT Member Posts: 5,865
    I don't believe the CGa has anything to control return water temperature.
    The lower the Limit setting, the more efficient the system will be. You want the lowest setting to satisfy the thermostat on the coldest of days. But, you want the return water temperature to be 135° or higher to prevent condensing of the flue gasses.

    The newer CGa boilers have the Eco dial that holds the burner off if there's useable BTU's left in the boiler to heat the space.
  • hot_rod
    hot_rod Member Posts: 22,262
    Between 130- 140F return within 10 minutes of run time is generally accepted as safe operating condition. The actual number varies a bit depending on fuel type, burner adjustment, etc.

    If the burner does not modulate you need to set it high enough to satisfy the heat load on your coldest (design) day.

    Of course the lower boiler operating temperature the better for efficiency, as long as you maintain that return temperature suggestion.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream