What is the optimum tempreture setting for a cast iron boiler

Jimbo_5

Its a WMc (CGa) in a one story house with a copper fintube loop. Just curious.

Jamie Hall

Return temperature not less than 160.

HVACNUT

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

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.