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Sizing for a Steam replacement boiler. will this work?

Joseph_4 Member Posts: 271
Hi. I have a customer with a steam system with 19 cast iron radiators whose edr comes out to 765 sq. foot. The boiler I'm looking at for technical reasons is rated for 733 sq. feet. I know from Dan's "Lost Art" that when sizing steam systems you go according to the connected load. However, I know from doing a heat loss that the radiators in each room in the house are grossly oversized. so do i care if say the last section on each radiator doesn't get hot. even if it does turn back to water before it gets hot. its overkill anyway?

Any input would be greatly appreciated




  • JStar
    JStar Member Posts: 2,752

    You want to cover the radiation load. HOWEVER, most manufacturer's sizing charts are based on a 33% pickup factor. If the piping is insulated, I only add 15%. Partially insulated, I add 20-25%. So, the next question is.....is the system piping insulated?
  • Joseph_4
    Joseph_4 Member Posts: 271
    the pipes are insulated

    Hi. yes the pipes are insulated in the basement. but the 765 and 733 is after you subtract the 33% pick up factor. In this house when i multiply 240 x 765 i get 183,600 btu and if i multiply that by 1.33 i get 244,188 btu. A crown ksz200 says the doe heating capacity is 235mbh and its net rating steam square foot is 733.

    or are you saying if pipes insulated i can multiplty 183,600 by say 20% or 1.20 and then i get 220320 btu in which case this boiler will do the job?
  • JStar
    JStar Member Posts: 2,752

    I would choose the KSZ200. Or you could install 2 KSZ090's and stage them for incredible system efficiency and fuel savings.
  • Joseph_4
    Joseph_4 Member Posts: 271
    Thanks for your input jstar

    i appreciate your input

This discussion has been closed.