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Sizing Replacement Boiler


I am looking to replace a steam boiler in my grandfathers house.

The current boiler is a Peerless 61-05 STDG-SP
404 Square feet Steam
97,000 BTU/HR OF steam

Natural Gas

I went throughout the house and calculated all the radiators using Weil McLain radiation sizing chart and came up with 326 square feet of steam 78,000 btu/hr.

Should I go with a boiler that matches my calculations or one that is a closer match what is in there?

I have pictures and more information if any one can help with some knowledgeable guidance



  • bburd
    bburd Member Posts: 912
    If the steam pipes are properly insulated, there is nothing unusual about the system and you are sure of your numbers, select the new boiler to carry 326 ft.² of steam.

    Oversizing of boilers and furnaces is an unfortunate but very common practice. It’s unusual to find a steam boiler that is not too large for the load.

  • HydronicGuru
    HydronicGuru Member Posts: 13
    I assume that since you are using a Weil McLain radiation sizing chart, you intend to install a Weil McLain steam boiler. If this is the case, you have a few questions to ask.
    1. Is this the original boiler to the system? Could someone else have calculated wrong.
    2. Are your calculations correct? I only calculate a difference of 78 Sq. ft.
    3. Do you plan to install a Weil McLain?

    Weil McLain would be an easier decision as the EG-40 is 325 Sq. ft. of steam with a 6 inch flue.
    While the EG-45 is 392 Sq. ft. of steam with a 6 inch flue. You would not want to lower from your calculations. However, 392 is now only a difference of 12 Sq. ft. from your current setup.
    Let's see what others suggest.
    EBEBRATT-Ed Member Posts: 15,524
    I would use the EG-40. Don't forget the boiler has a 33% pick up factor built in
  • KC_Jones
    KC_Jones Member Posts: 5,737
    edited February 2021
    Agreed, with a calculation of 326 get the EG-40, no way would I go to the 45 for 1 sq ft of radiation.

    From everything I’ve heard, read, and seen, I’d assume the previous boiler is always oversized.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15