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U.S. Radiator Corp 20-4 Steam Boiler

JS41190
JS41190 Member Posts: 8
in Strictly Steam

Hello,

I’ve recently come across this 20-4 Steam boiler that is finally in need of replacement after decades of service. It is oil-fired and will be converting to natural gas. My question is, how do I size this new boiler based off of the old rating plate? The home has steam in some areas, and hot water baseboard in others.
If anyone can point me in the right direction, that would be great!

IMG_2020.jpeg IMG_2016.jpeg

Comments

  • mattmia2
    mattmia2 Member Posts: 13,110

    measure the edr of the steam emitters connected to the boiler.

    I wouldn't worry about the hot water loops unless it is over 30% of the output if the boiler and even then it won't be an issue unless the edr just matches the heat loss of the building. you could do some comparison of the output of the boiler to the heat loss of the building, as long as the boiler is bigger shouldn't be a problem.

    JS41190EdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 10,609

    How is the water loop connected to the boiler?   Does it use the tankless coil that was intended for DHW use?  That will determine if you need a replacement boiler with a tankless coil.  

    Regardless, you have an opportunity to do a better job than the previous installers that added a water loop.   If you must use the water loop for a specific area of the building where any of the radiators are above the boiler’s water line, you should consider making that water loop a pressurized closed system where the tankless coil is the source of the hot water for that space.  That will always be a better design.  I can provide more details if needed.

    If that tankless coil is there for DHW, you might consider a separate DHW tank tha uses gas. That way you don't need to keep the boiler at 160° all summer long.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 10,609
    edited June 16

    Also @mattmia2 has the best idea for selecting the proper size. DO NOT USE THE OLD BOILER's RATING to select the replacement boiler.  Have someone with experience count the EDR of the connected radiation.  The reason I recommend having someone with experience count the radiator’s dimensions and number of sections in each radiator.  I have seen too many DIY installers make a mistake in selecting the correct EDR number for their radiators because they have not actually looked at any other radiators to compare the drawings to.  Columns v. tubes v. thin tube… can be deceiving if you have not actually experienced the multitudes of radiators that are available. 

    Screenshot 2025-06-15 at 10.10.11 PM.png Screenshot 2025-06-15 at 10.10.22 PM.png

    Then there are those that try to do extra math only to make the mistake bigger. Once you have the EDR of your connected radiators total Square Foot, you select a boiler that will match that number in Square Foot of steam. So… forget steps 8 and 9 in the guide above because they really have a Square Foot of steam rating for every steam boiler made for heating homes. there is no need to convert anything to Gallons per hour of oil or BTU per hour for gas. Just match the Square Foot of steam rating of the boiler to the Square Foot of EDR in your home. It is that simple.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    JS41190weakoak1124dabrakeman
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 18,002

    OMG, I remember pulling the tankless coil off of one of those. I think it took two of us to lift the dam thing. The customer wasn't getting HW so we pulled it off to clean the muck out of the coil. About 1/2 the bolts broke so we spent the day drilling and tapping. Not fun. This was back in the 70s when we tried to fix things. You couldn't find anyone to try that now

    EdTheHeaterMan
  • mattmia2
    mattmia2 Member Posts: 13,110

    Is the decorative burner compartment on that like the size of a phone booth?

    EdTheHeaterMan
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 18,002

    a lot of the old boilers had the extended jacket. I guess they wanted everything to look good. Just made it harder to work on everything

  • mattmia2
    mattmia2 Member Posts: 13,110
    https://forum.heatinghelp.com/discussion/comment/1858022#Comment_1858022

    My grandparents has an oil furnace like that from 1950. I think it was a lennox, remember it was some super stylized chrome nameplate that I had trouble reading as a kid. It was huge and looked like the jacket was assembled from numerous square panels screwed together. It had a damper that blocked off half the plenum for the ac coil in the summer.

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 10,609
    https://forum.heatinghelp.com/discussion/comment/1858024#Comment_1858024

    Your comment about your grandparents heater brought back a fond memory of playing at grandmother's with a large barrel of marbles. Read this old post:

    https://forum.heatinghelp.com/discussion/comment/1702214#Comment_1702214

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

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