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Boiler Sizing

SilvionSilvion Member Posts: 26
I had someone look at my boiler today that is a weilmc 578 steam boiler that he says is oversized.

If I use the EDR approach I have 24 Radiators. Each radiator gives me a BTU output of 3600. So total would be 86,400. I have 4 risers for two floors. The boiler is in the basement.

Its an older brick home with not insulation on the other walls. It has 8 small one bedroom apartments. Each with 3 radiators the tall column style. 4 apts on each floor. The hallway has no radiators.

Do you guys think a 521,000 is oversized or apropiate for this building?



  • Paul SPaul S Member Posts: 1,219
    something wrong

    something is wrong with your EDR calculation of each radiator.....521,000 btus would be 6 times your calculation over for the SQ FT  of each radiator....once you get SQ FT of radiators multiply by 240 to get BTUS for steam....then use a pick up factor on certain instances... the heating pro that came to look at the boiler did he properly measure the SQ FT of the radiators himself??? if not you should find someone else ....Steam boilers need to be installed and piped a certain way....he may not be your best choice...

    PAUL S
    ASM Mechanical Company
    Located in Staten Island NY
    Servicing all 5 boroughs of NYC.
    [email protected]
  • nicholas bonham-carternicholas bonham-carter Member Posts: 6,535
    24 radiators

    Are you sure of the BTU ratings for the radiators. Go by the square ft. of EDR, then compare the total square feet of the radiation to the rating of the boiler for it's EDR. The boiler rating in square feet has the pickup factor built in.

    The question is not whether 521,000 BTU is oversized for the building; but rather does the boiler output match the total EDR of all the radiators and pipes.

    When you get your new boiler, make sure you get some extra main (not rad) venting, as you have probably paying extra to the fuel company to remove the air from the system as it start to steam. Installing a 0-3 psi gauge along side the useless 0-30 psi gauge will show you when you have stopped paying extra!--NBC
  • SilvionSilvion Member Posts: 26
    boiler size

    ok let me recalculate
  • BobCBobC Member Posts: 4,406
    Are those radiators

    - 38" tall

    - have 3 columns per section

    - have 3 sections

    If the above is true than those 24 radiators each have 15 sq ft of EDR. Twenty four of them means you need a boiler that is rated at or above 360 sq ft of steam.

    What kinds of problems does the system have, does it short cycle? Post some pictures so we can see what your dealing with.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Jamie HallJamie Hall Member Posts: 6,653
    Something very wrong

    with your EDR figures, I think.  As NBC says, the EDR of a radiator is the effective radiating surface area of the unit -- not the face area.  Even a very small (5 section) typical radiator has an EDR of about 18; most normal radiators are around 40 to 50.  Big ones can easily go twice that (I have three which are over 100 each).  Your calculations work out to an EDR of only 15 for each radiator!

    Much the easiest way to figure boiler size is directly with the total system EDR, as the boiler ratings for EDR have pickup and other odd factors built in. 

    Let us know how your recalculation goes!

    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
  • SilvionSilvion Member Posts: 26
    Boiler Size

    The Boiler has a Steam Sq ft of 1629

    I have 24 radiators that that 3 columns each.

    The tallest one is 38 inchest. It has 3 columns total. That has a EDR of 5 per column.

    So 5x3=15 times 24 radiators gives me a total EDR of 360.

    So is this boiler that oversized???
  • SilvionSilvion Member Posts: 26
    boiler size

    This picture is a little fuzy. I will post better ones tomorrow.

  • Jamie HallJamie Hall Member Posts: 6,653
    Well now...

    those are tiny radiators, if my vision doesn't fail me.  Your calculations for EDR may be pretty close!  Great.

    In which case, however, your boiler is wildly oversized.  Double check everything, but then try to get a boiler which comes very close, in  EDR rating, to your real numbers.  You'll be much happier and so will your steam system.

    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
  • SilvionSilvion Member Posts: 26
    Boiler Size

    This is the biggest radiator in the entire building. The others are smaller than this. Some are the same size. So if we go by this one for the entire building this radiator has a EDR of 30. Its 38 inches high, 9 inches wide. So thats 5 EDR per section and this has 6 for a total of 30.

    So all 24 radiators if they were this size would give me a edr of 720. If I do the exact calculation it will be much less. But lets use 720 for now. My boiler has a 1629 sq.

    More than double!!!. How can this be??


  • SilvionSilvion Member Posts: 26
    boiler size

    second photo
  • SilvionSilvion Member Posts: 26

  • EricEric Member Posts: 261

    here.... read this article:

    (from the resource link here)
  • nicholas bonham-carternicholas bonham-carter Member Posts: 6,535
    edited October 2013
    Wildly oversized boiler

    If you have the Weil McLain series 78 boiler, it would have a power burner in it, and could be down-fired to some degree to alleviate the over sizing. Are you burning oil, or gas?

    In addition to that, it would be most important to have your steam supply piping, and main venting in tiptop shape. Send us a picture of your boiler so we can see any problems which may be lurking.--NBC

    P. S. Here is the manual for your boiler, and hopefully the installer was able to follow instructions for piping, even if he did not read their instructions on sizing the boiler!
  • SilvionSilvion Member Posts: 26
    boiler sizing

    one thing I forgot. this boiler did make hot water. not now. I have 2 separate hot water tanks.

    So does the mass btu account for hot water?
  • nicholas bonham-carternicholas bonham-carter Member Posts: 6,535
    DHW factor

    If the installer incorrectly loaded up the boiler capacity for the additional hot water production, then that may account for the over sizing.

    See how far you can down size the burner, and you may want to use this BTU 's to once again make hot water.

    Is this a new to you building, or was the boiler installed on your watch?--NBC
  • SilvionSilvion Member Posts: 26
    Boiler Size

    When I bought the building This boiler was there. However I had a Dual Power Flame Burner. Model wcr1-go-10.

    It was working fine for a few years. It was strictly on oil. I had a Heat Timer which is now disconnected. The first few years I was using around 2500 gallons of oil. Which I thought was normal. I had never dealt with oil. Then the burner stopped working properly. I could not find a tech who could fix it properly. So i took it our and installed a beckett oil burner and seperated the hot water into two tanks.

    I thinking maybe I can use the powerflame burner again but use the gas side, since gas would be easy to ignite. The problem with the oil side was that the burner could not ignite properly.

    Or maybe just downsize the nozzle on the beckett burner and use oil for this winter.

    Lots of choices.
  • nicholas bonham-carternicholas bonham-carter Member Posts: 6,535
    Burner adjustments

    Most likely, you have some oil in the tank, and as it is so close to winter, you may want to continue with the oil for this winter.

    Burner work is highly technical, and requires the use of proper combustion analysis equipment, especially when down firing. Check with W-M, and the burner mfg, to see how far down that model can be reduced.

    When people are having problems with a steam system, they will often put in a heat timer control to compensate for an imbalanced system. As a result, the situation is frequently made worse. There is probably a sticker on the boiler showing who installed it (unless in their embarrassment they scraped it off!), and so you know who not to call.

    You could calculate your building heat loss and compare that to your oil consumption/square feet/degree days, and see how much gas you would burn (and cost) when everything is running right.

    What is your location, maybe there is someone on the" find a pro " button here at the top.--NBC
  • SilvionSilvion Member Posts: 26
    Boiler Size

    Im in East New york Brooklyn, I will check the wall.
  • gennadygennady Member Posts: 677
    column or section?

    you get rating per section not per column. Please multiply to sections quantity
    Gennady Tsakh

    Absolute Mechanical Co. Inc.
  • SilvionSilvion Member Posts: 26
    Heat Timer

    Your right about the heat timer. For what ever reason I burned more oil using the timer than a regular thermostat.

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