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under + over sized steam boilers

have a company overing to sell me a steam boiler that is a 225K BTU to replace a 200K BTU existing. what are the consequences from using boilers not the correct size? thank you for your input.


  • crash2009
    crash2009 Member Posts: 1,484
    We still didn't get an answer

     from the last question we asked you, so I'll ask it again.

    What is the EDR of the building the proposed boiler will be going into?
  • Dave in QCA
    Dave in QCA Member Posts: 1,785
    edited October 2012

    If you don't already have the information to calculate EDR, this might help.  EDR is the surface area of the radiators stated in sq ft.  The first is from an old version of the ASHRAE Guidbook.  The second is from Peerless Boiler and contains some VERY important information on the proper installation of steam boilers.  The third is a simplified chart for calculating and adding up the total EDR of the system.
    Dave in Quad Cities, America
    Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
    System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
    Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
  • robert borders
    robert borders Member Posts: 48
    under + oversized steam boilers

    i  have just received holohans book the "lost art of steam" and waiting on the book from him also, EDR (Every Dam radiator). Reading at breakfast that it is indeed the radiation that is just as important or more so than the heat loss. plus a 1.5 factor on the DOE rating if i remember correctly.

    i have an weil mcclain eg 55 located and the dunkirk wholesaler has a 225K BTU he wants to move out of inventory so figuring the 55 to be 200K BTU, wondering if 25K BTU will cause a proble? since the book was sent priority mail,,i should have it monday to see what the sq ft is in this big 2 story 1876 magnificient home built by a returning civl war officer in keokuk ia. it is listed on the national registration of homes. i have a new home + would trade for it since it has so much character.
  • BobC
    BobC Member Posts: 5,473
    The problem is

    that a lot of steam boilers that are now installed are just to big for the load they are driving. The edr of the house is all the boiler has to work with and if the boiler is to large it works but it's not very efficient. If the boiler is grossly oversized it won't work well at all.

    Make a list of all the radiators (height, depth, number of sections and the number of columns per section). With that information you will be able to tell what kind of load you have to drive and thus what size boiler you need.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
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