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Electric Boiler Low vs High Mass?

JasonN Member Posts: 2
My house has an electric boiler with multiple options for high and low mass settings. My house has roughly 20 gallons in the entire system. The house is older (build in the 20's I believe), and has radiators to transfer the heat to the house. Here is a link for my boiler.


Now, on the front, there is a sort of 'knob' to pick high/low mass settings. They are temperature settings from roughly 110 to 180 degrees. The boiler itself only holds around 1 gallon if that. I honestly have no idea what this should be set at. Any help would be greatly appreciated.



  • Jamie Hall
    Jamie Hall Member Posts: 23,426
    What kind of radiators are they? Big old cast iron ones? If so, logic -- completely uninformed by reality, mind you, suggests high mass. However, reading through the manual suggests -- even more strongly -- that you want the low mass setting, as that seems to be more like what one would run a more conventional boiler at.

    I'm open to suggestion!

    Try it both ways, and see which keeps you more comfortable...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Gordy
    Gordy Member Posts: 9,546
    Rodger that low mass setting.
  • JasonN
    JasonN Member Posts: 2
    They are older cast iron radiators, but I would not call them huge. Thanks for the input guys. :smile:
  • SWEI
    SWEI Member Posts: 7,356
    The electric boiler manufacturers are at least a decade behind the curve here with their control settings. Page 10 in the manual shows a series of curves, from which you need to pick the one that most closely matches your required supply water temp at design conditions.

    If you don't have a room by room heat loss calc and an EDR survey of the existing radiation along with the knowledge of how to use those, here's the short version:

    Wait for a cold week. Turn your thermostat up as high as it will go.

    Adjust the dial during cold weather until the house is comfortable. Remember that it takes several hours for the mass of your house to reach thermal equilibrium. Refine as needed, particularly when the weather gets colder.

    Set the thermostat 2-4°F higher than what it reads when the space is comfortable. Now forget about it.