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boiler sizing

STEAM DOCTOR Member Posts: 1,973
I was recently hired to do a consultation on an old house renovation. The homeowner doesn't trust the people that the general contractor is bringing in and I am getting the impression that the GC also doesn't trust the people that he is bringing in. They are replacing the  old massively over sized oil boiler with a new gas boiler. They only want to go with burnham because the local gas company gives a rebate for on the burnhams. I did an EDR survey and came out with 148 mbtuh. I told them to go with the IN6 which is rated for 144mbtuh. The problem with the IN6 is that the manual only requires one 2" riser from the boiler. My gut tells me that this is to small. There is no way that I will be able to  get the boiler installer to exceed the manufactures recommendations.I am wondering if it is worthwhile to tell the installer to use the IN7 which on one hand would be over sized but on the other hand would require him to use two 2" boiler risers as per manufacturers recommendation. Thanks in advance for the advice and input.


  • Greg Maxwell
    Greg Maxwell Member Posts: 212
    boiler size

    When you size the boioler, go by square ft steam, as far as the boiler riser goes, dont worry abour a 2" riser, use that to go to a 2-1/2" or 3" header.
    STEAM DOCTOR Member Posts: 1,973
    please see entire post

    I am not the installer. no way I can get installer to do more then minimum required by manufacture
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,322
    If the manufacturer says 2" is fine and it

    is a counter flow system then it will be fine. As long as the rest of the piping is as it says it should be. Is there plenty of rise to the supply from the water line? Minimum works fine as long as it is reached. I would go with the boiler the right size. over sizing to get a larger header is good for no one.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • patrick linhardt
    patrick linhardt Member Posts: 134
    question of velocity

    Your gut is concerned with the single 2" riser, as was I. However, doing the math results in a steam velocity of 43.5 feet per second (fps). I like to keep it under 50 fps, so that is adequate.

    For better performance, steadier water line and drier steam, velocities under 25 fps are recommended. The Dead Men used velocities as low as 10-12 fps.

    The math on the IN7 comes in right at 25 fps. I'll let you make the call.

    I have attached two pages from my book, Linhardt's Field Guide to Steam Heating, that deal with this issue. It is available on this site.
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