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IBR calcs and boiler size

Mr Takagi
Mr Takagi Member Posts: 26
I am trying to find out for sure what size of boiler to use as a replacement in a converted gravity system. By calculating the EDR of the cast iron radiators I came up with 108,000 BTU. Using the Slant Fin I=B=R Heat loss form, I come up with 78,000 BTU/hr. I don't know if it makes a difference, but the total system volume is approx. 150 gallons of water. The Dunkirk Quantum 100 I am considering has on IBR output of 78MBU, and Heating output of 90MBU. Is this reasonable? Or should I be looking at something with an output to match the radiation?

Thanks for the help



  • That's the right size.

    I wish it were a different brand, but I can't win 'em all....


  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    When it's a water system concern yourself with heat loss-not potential of the radiation at some fixed output level like 180°. Just because you can run the radiators that hot (or even hotter) doesn't mean that they have to be at--or even close to--that temp to meet the heat loss of the space.
  • Mr Takagi
    Mr Takagi Member Posts: 26
    Slant Fin

    Sorry Noel, nothing against Slant Fin. I'm only considering the Dunkirk because I need to eliminate the chimney and vent through the sidewall. And with a condensing boiler, I can avoid any Pri/Sec piping and keep it simple - just one big zone in this old house.
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