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Help with sizing steam boiler

Can someonehelp me figure out what the proper size steam boiler is for my condo building?


I have measured the radiators like suggested. 


W: 6"

# of tubes: 5

# of sections 16.

2 radiators per  condo, 10 condos, 5 floors. Not sure if this is important but each condo is approx 725 sq ft.



    Can you post some pics of rads so we can be sure that the radiators have tubes and not columns? There is a big difference.
  • KD_2012KD_2012 Member Posts: 9
    Radiator Pictures

    Thanks for the help!
  • KD_2012KD_2012 Member Posts: 9
    Radiator Pictures

    Thanks for the help!
  • crash2009crash2009 Member Posts: 1,484
    edited February 2012
    38.4 EDR for that one

    Sounds like you have the thin tube if the legs are 6" wide.  Look on page 2 of the chart I sent you.  25" tall by 6" wide, equals 2.4 EDR per section.  You say you have 16 sections, 2.4 times 16 equals 38.4 EDR for that one.

    Do the same calculation for all the radiators and add them up.  This number will be the total EDR for the building.  When you have arrived at the total EDR for the building, we will show you the next step
  • KD_2012KD_2012 Member Posts: 9
    Total EDR

    In doing the calculations that you asked, my total EDR is 768.

    Thank you for the help.  As I am someone who has only learned about boilers because of this issue, this is definitely daunting!
  • crash2009crash2009 Member Posts: 1,484
    245 MBH

    Next there is 240 btu's in each foot of EDR (240 X 768 = 184,320).  Then there is the pickup factor of 1.33 (this is where the pro needs to be onsite to figure if you need to use 1.33)  184,320 X 1.33 = 245,145.  You would need a boiler with a DOE Heating capacity of 245,145.  Also known as 245,145 btu's/hr.  Might also be shown as 245 MBH.  Have a look at Daves chart  He lists the DOE as Gross Output (probably a better term).  This chart will give you a starting point of what models you will be looking at when your pro decides what you need.  Here is a shortcut to the entire thread  You understand this is just a ballpark number, you need to have a pro decide what you need.
  • KD_2012KD_2012 Member Posts: 9
    Is a bigger boiler better? or worse?

    Thank you for your help with this.  Here are a few more questions...

    1- Of all the ehating/Plumbing companies that gave us quotes, no one measured our radiators. Only one company asked us the SQ FT of our units so they could "cube" the building and determine size of the boiler.  Does "cubing the building" work for sizing boilers too?

    2- Most of the companies looked at what we had currently a 600k BTU and were just replacing it with something of similar size.  Either a 550k Weil McLain or a 625 Peerless.  Based on the quick calculation you just help me with, (I know it is back of the envelope) It seems we would require a smaller boiler than what the contractors are  suggesting.

    -  I understand that if the boiler is too small it wont heat the building properly, what happens if it is too big? Is that bad? 

    3.  We all felt the heat in the building prior to this issue was way too hot - is that because a bigger boiler produces more heat which may not be neccessary?

  • crash2009crash2009 Member Posts: 1,484
    Try the find a contractor link

    1-Not measuring is the fastest way to loose the deal.  Cubing doesn't work.

    2-Selling what was there before doesn't work either.  It's not surprising to me that you would need something smaller than what you have.  I don't know about too small, but I do have experience with too big.  It's called an "oversized boiler" and if you research that term here at the website you will read about all the horror stories. 

    3-An oversized boiler can heat the place properly without overheating but it's a pain in the neck, it needs a lot of babysitting. 

    What City and State are you in?  Maybe there is someone from around here that could help you out.
  • boiler replacement

    will you be making hot water with this boiler? sometimes it helps not to have a second flue to worry about.

    i think i see from the pictures that you have a 1-pipe system, so don't immediately have them change the radiator air vents, but wait until the main air vents are checked/improved. there may be an improvement by putting air vents on the riser tops to get the air out more quckly.

    what controls the boiler now--thermostat?

    it is most important to to specify that the contractor install the boiler exactly according to the instructions from the manufacturer, as some deviations may invalidate the  warranty!!!!!!--nbc
  • Jamie HallJamie Hall Member Posts: 6,655
    Boiler size

    it is really rather important that the boiler be sized to the radiation it's feeding -- and nothing else.  Boilers are sized both by BTU, but also by the EDR of the system they're feeding -- and that EDR rating nicely includes things like pickup factor and so on.

    The way I read your arithmetic, your existing boiler is considerably oversized; if someone suggests replacing it with the same the only people who will benefit are the fuel company and the guy selling you the boiler.  And oversize boiler is a real nuisance, and is inefficient on top of that.

    The building being too hot is not, however, a matter of boiler size, but a matter of control -- particularly where the main thermostat is (assuming there is one) or how the heat timer is set up, if that's what's being used.  A pro. can address that too -- and the Wall will be happy to help too!

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
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