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Convectors

347
347 Member Posts: 143
in Strictly Steam
Have a steam boiler short cycling on off every 30 seconds or so. Water line is not jumping around, all convectors have working vents, steam main vented. Boiler is 479 edr. House has 7 small convectors. I'm trying to figure the connected edr. Looking in Dan's book EDR I found many convectors that could match, they all have a little different edr. I'm not sure how to tell which convectors are on the job. I should I use the avg from two in the book? As of now I'm thinking the boiler is over sized.
Thanks for your help.347

Comments

  • lchmb
    lchmb Member Posts: 2,997
    is this a new system? Is this an old system with a new problem? Pictures?
  • Fred
    Fred Member Posts: 8,542
    Post a few pictures of the convectors. A boiler rated at 479 Sq. Ft. of steam will probably be way over sized for 7 small convectors. Do you know if the boiler has ever been down fired or if it has a two stage gas valve on it? Pictures of the boiler would be helpful also. As Ichmb asked, is this a new issue? A little history would also be helpful.
  • 347
    347 Member Posts: 143
    Boiler was an oil o gas replacement done 3 years ago. Don't have any pictures at this time of the boiler or convectors. I don't belive it has a two stage gas valve. It's a burnham in series boiler. It has one 2" outlet with an 2" equalizer, 1" wet return at the water line.

    I'm not sure if it's an new issue, but when the homeowner went to check the water level she heard it turn on and off quickly. They left the boiler off fir a day or two, turned it on and if fired for a while , turned off the started to short cycle, I confirmed that yesterday. The pressuretrol is set properly and is working as it should. I'm thinking it's been this way from day one, but they just noticed it by chance.

    Thanks
  • delta T
    delta T Member Posts: 884
    well if the boiler is vastly oversized for the load, then short cycling is inevitable. Given that 479 sq ft boiler, your 'small' convectors average about 68 sq ft being delivered to them, that seems like a large convector to me....if you take a guess, how much is the connected load based on the numbers you get from E.D.R., you will likely be in the ballpark.
  • Steamhead
    Steamhead Member Posts: 17,314
    Just use whatever is closest to the convectors you have- length, height, depth. It shouldn't be that far off. Let us know what you come up with.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • Fred
    Fred Member Posts: 8,542
    In the meantime, until you figure out a long term fix, don't use setbacks on your thermostat or shut the boiler off. Set the thermostat to a house temp that is comfortable for you and leave it there. When you use set-backs or turn the boiler off completely, it allows the house temps to drop and recovery requires the boiler to run a long cycle. That's when short cycling on an an over-sized boiler is most pronounced.
  • gerry gill
    gerry gill Member Posts: 3,078
    if you size a steam boiler according to the IBR sizing methodology, and you have convectors with tubes and fins, i guarantee you boiler will be oversized.
    gwgillplumbingandheating.com
    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

  • 347
    347 Member Posts: 143
    Long day today. I'll be putting the edr numbers together tomorrow. I'll keep you posted.
    If it is oversized, what could be done to help the short cycling?
  • Fred
    Fred Member Posts: 8,542
    It can likely be down fired some or a two stage gas valve installed. In both cases, someone who is proficient at doing a combustion analysis is required to make it safe.
  • gerry gill
    gerry gill Member Posts: 3,078
    sometimes we have to remove the outer burners and plug the orifices.
    gwgillplumbingandheating.com
    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

  • 347
    347 Member Posts: 143
    I was able to get full aces to one convector and messured depth, height and length, the others I got height and lengths but not depths (too much stuff to move). I'm assuming that the depths are the same for all. The total edr I got was 367.
  • Fred
    Fred Member Posts: 8,542
    Well, It's over-sized but it's in the range where it should be able to be down-fired. Work on getting it skimmed well and see how it runs after that, then have someone look at either down-firing or two stage gas valve.They won't be able to do that with it running like it is now.
  • 347
    347 Member Posts: 143
    Would love to skim it, but has no skim port. I'll need to put one in. I'll look into the two stage gas valve option.
    Thank for the help.
  • BobC
    BobC Member Posts: 5,495
    Get someone that knows what they are doing and see if the boiler can be downfired and ask him about two stage firing the firing (that will probably not be cheap).

    In either case get a skim port installed. The boiler will NEVER work right until it is clean.

    Bob
    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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