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Short-cycling, wet steam and boiler sizing

David_14 Member Posts: 10
My oil-fired boiler is short-cycling and my air vents are gurgling. Here is what I've done so far:

-New air vents on all radiators (Gorton - various sizes)

-New main vents (2 Gorton #2 on each of 2 long mains)

-All pipes are insulated

-All pipes and radiators are pitched

-New chimney liner

While each of these steps has led to significant overall improvement, I'm still not at the point where my system seems to be running correctly. But that water hammer has decreased a lot! And no more cold radiators.

It was suggested to me by a local pro to downfire the boiler. He suggested this over the phone, and after recalling information in We Got Steam (currently loaned to a friend!) and reading more on this site, I think it might be worthwhile to measure the entire system and do some calculations first. It seems possible that a different sized boiler might result in a more efficient system. I'm not keen on springing for it, but perhaps I could sell the ~2 year old current boiler (which the previous owner had installed). Of course, if downfiring is a reasonable solution than that would be great too!

My Questions:

-Should I try having the boiler downfired without measuring all the piping and radiators first?

-Is measuring the system something I can do myself? (I'm a reasonably sharp guy and work with statistics daily - but I'm a homeowner not a heating pro)

-If it is something I can do, what measurements do I take?

-Inside diameter or outside diameter?

-How accurate do I need to be on pipe lengths? My mains and some of my risers are covered in asbestos and some are hard to reach. If I'm 1-2 inches off on the length here and there, is it a big deal? I realize being off on the diameter would result in significant error.

-Is there a "How-to" posted somewhere?

-And do I need to buy the EDR book, or can I post the measurements for some help here?

-What else might I want to know?

-What other information do you need to help me?


p.s. Thermostat seems to be well-located. Not on an outside wall or cold/drafty spot.


  • Fred Harwood
    Fred Harwood Member Posts: 261

    Before downfiring, calculate the radiation EDR and compare it to the boiler's EDR rating. You should not downfire more than 15 percent below the boiler rating. Also, do you have a Vaporstat to keep pressure below one PSI?
  • David_14
    David_14 Member Posts: 10

    No vaporstat yet. Pressuretrol is set at about 1psi because any lower and the system doesn't turn on for some reason. Once I figure out whether or not I need to downsize the boiler I'll consider a vaporstat to allow more precise control. I'd rather generate ounces than pounds.

    Looks like I still need guidance on how to measure the system. If someone can run down my list of questions it would be great. Thanks!
  • David_14
    David_14 Member Posts: 10

    Thanks, Fred. No vaporstat. Pressuretrol is turned down to about 1psi. For some reason, the boiler won't turn on with it set any lower.

    I do see the value in a vaporstat, but want to be sure I'm keeping this boiler before investing.

    Looks like I still need more information on how to do the measurement. If someone is able to run down my list of questions above that would be great. Thanks!

  • michael_15
    michael_15 Member Posts: 231
    just the radiators

    I'm not sure you need to measure the pipes to check the boiler size since that's usually accounted for with pickup factors and so forth. There are various small lists of EDR by radiator you can get on the web (none totally complete that I've found, unfortunately). For example, try googling for "htghelper" and taking the link that shows up.

  • Doug_27
    Doug_27 Member Posts: 2

    Here's a page on how to calculate EDR:

    Once you have it, that should be the same or slightly less than the net BTU rating of the boiler. The DOE rating (gross rating) will include the pickup factor for the piping.
  • David_14
    David_14 Member Posts: 10
    Do I need to replace my boiler?

    OK, I've measured my rads and calculated the total output using the directions from the link Doug provided. Do I need to replace my boiler, or can I have it downfired? I'm not sure which boiler manual figure to use. If it is 174000, then it seems I need to replace my boiler so I don't violate the 15% guideline provided by Fred. However, I suspect the number I should use is 131000 - which seems to be good news to me because it means I can downfire without exceeding 15%.

    Total Radiator BTUs = 119,796

    I currently have a Weil-McLain SGO-5 boiler. From the manual:

    I=B=R Burner Capacity GPH = 1.45

    DOE Heating Capacity MBH = 174

    Net I=B=R Ratings:
    Steam Sq. Ft. = 546

    Steam MBH = 131

    DOE Seasonal Efficiency % AFUE = 83.9

    My hot water also comes from this boiler (tankless). Not sure if this is relevant.

    From the tag from the cleaning on 11/4/04:
    (Note: hard to read handwriting, but this is best guess)

    Smoke 0

    Draft .12 (I installed a damper shortly after this - pro calibrated but I don't think he updated the tag)

    Temp 400

    CO2 12%

    EFF 83.75

    135 X 80A

    Here are the sizes of my mains (not including risers). House is 2 floors.

    527" @ 2.5" O.D. *plus* 245" @ 2" O.D. (772")

    497" @ 2.5" O.D. *plus* 503" @ 2" O.D. (1000")

    Thanks for whatever advice you can provide!
This discussion has been closed.