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Why steam boilers short-cycle

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HeatingHelp
HeatingHelp Administrator Posts: 650
edited October 2016 in THE MAIN WALL
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Why steam boilers short-cycle

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  • Furnacelady
    Furnacelady Member Posts: 29
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    With the advent of the digital thermostat don't forget to change the software from forced air gas furnace to boiler on the cycling. Cycling is called many different names by different thermostat manufacturers.
    hot1
  • Bev
    Bev Member Posts: 1
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    Steam boiler. One pipe System. System short cycling. Air vents good, releasing air. All radiator's hot. Pressuretroll: Cut in: 0.5. / differential: 2. Site glass water level - good. Utica Starfire II. New honeywell thermostats dial from Home Depot. System skimmed. New cad. 4 on/off cycles in 35 minutes. Any idea's would surely help. Thank you.
    misterheatjustin1122
  • Jamie Hall
    Jamie Hall Member Posts: 23,449
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    If all the radiators are hot... you may not have any real problem. Sort of. Two things I see right away, though -- the differential on the pressurestat is too high; it should be 1, not 2. And you should check and make sure that the thermostats are correctly set for steam.

    Now. Having done that -- to go further with comments, we would need to know what the total installed radiation is in terms of "EDR", and what the boiler rating is, also in terms of EDR. The latter should be one the boiler; the former you can wander around the house and add up. The other relevant question at this stage is does the cycling begin once all the radiators are pretty well warmed up, or does it begin much sooner?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mitch101
    mitch101 Member Posts: 22
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    I'm stuck with an oversized boiler because the installer passed away and his company disappeared. I have huge main vents and working radiator vents. My thermostat is set to steam heat cycling. Pressuretrol set to .5 cut-in and 2.0 cut-out. I have a 2 degree setback on the thermostat to minimize short cycling and just live with it. To reinstall would cost thousands more than the gas wasted.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
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    How oversized is your boiler in EDR?
    Any time the boiler has to increase the building temperature, there will be short cycles, with subsequent inefficiency. Set it and forget it would be best.
    Have you looked into having your boiler down fired?—NBC
  • SteamHeat
    SteamHeat Member Posts: 159
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    Bev,
    Most modern Honeywell thermostats only have a 1 degree differential / swing. Try Aprilaire or Robertshaw thermostat and set a 2 or 3 degree differential. Hope this is of help.
  • BumpyHed
    BumpyHed Member Posts: 7
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    Agree with my fellow Steam Heads. Great questions to be answered before being convinced of oversized Boiler & Short Cycling. Huge Main Vents. Makes one think Big uninsulated piping big Radiators big drafty old style home with possible big hole in cold drafty wall behind thermostat. Etc. Yes great questions. Best of Luck.
  • jumper
    jumper Member Posts: 2,289
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    SteamHeat said:

    Bev,
    Most modern Honeywell thermostats only have a 1 degree differential / swing. Try Aprilaire or Robertshaw thermostat and set a 2 or 3 degree differential. Hope this is of help.

    Good idea for any heating system. Where to locate thermostat is the question?

  • meticulousmike
    meticulousmike Member Posts: 31
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    thank you for the share.this is good to know.i can share it with a customer to explain to them why it's not working correctly and also that i don't become one of those hapless repair guys.i always exercise extreme caution with stuff that i don't know.it's all about safety for me and others and not just about getting paid.i need this info cause i am still a baby when it comes to steam boilers ,they always got me scratching my head.i go by what i see that needs repair or replacing,so i always assume that whoever installed it did it right so i don't have to figure it out for myself but what happens when there has been too many repair guys hacking it all up over the years?..i go in to try and correct the issue as best as i could with what knowledge i've gained over the years.,that's how it works.getting the right info from a trusted professional source is another thing.up here in albany,ny there aren't many steam boilers so over the years of running my small business i've almost perfected my hot water boiler practices, i understand them well enough to get them to run good if not better.in schenectady,ny it's another thing cause they are mostly all steam or furnaces.i didn't have much practice on steam so i don't know all the ins and outs with em'..i have to keep learning and practicing..never give is my motto even if it kills me, i do pay dearly with all the hours and aches and pains,lol.but i'm only 50 years old..it's gonna take more years to get it, i hope it's not too late to continue.i'm a fighter that's because i was born and raised in da' bronx..haha!..thanks dan!

    There was an error rendering this rich post.

  • vhauk
    vhauk Member Posts: 84
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    I am a firm believer that the pressure should NEVER be raised. Water is a fluid that reacts to pressure. If you apply a deep enough vacuum to water it will boil at temperatures below freezing. Conversely, if the pressure is raised about 1 bar, the boiling point of water also goes up, above 212 degrees. Any liquid water that is under pressure and above its normal temperature of vaporization will instantly turn to superheated steam if the pressure is released. The result is…….explosive.
  • JoeEngineer
    JoeEngineer Member Posts: 17
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    A brief but thorough explanation brief, wonderfully simple. Thanks Dan
  • Intplm.
    Intplm. Member Posts: 2,009
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    @DanHolohan Your articles, always a pleasure. And @Erin Holohan Haskell thanks for posting. It is refreshing how well things are explained by your dad.
    His articles, as this one have made me better at what I do for decades.
    Henry
  • ethicalpaul
    ethicalpaul Member Posts: 5,737
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    Posted 8 years ago :joy:
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • Intplm.
    Intplm. Member Posts: 2,009
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    Posted 8 years ago :joy:

    Yes. I remembered reading it in the past and was such a nice reminder again here.
  • Erin Holohan Haskell
    Erin Holohan Haskell Member, Moderator, Administrator Posts: 2,326
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    Thanks for reading and for your kind words @Intplm.

    President
    HeatingHelp.com

  • DanHolohan
    DanHolohan Member, Moderator, Administrator Posts: 16,548
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    Thanks!
    Retired and loving it.
  • Koan
    Koan Member Posts: 439
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    Is it also possible an oversized boiler could exacerbate a cycling problem? This seems to be the case for my home if raising the temperature more than 2 or 3 degrees. We have 399 EDR of radiator surface area and a 750 EDR 300k Btu 1969 American Standard boiler 2 pipe vapor system. Vaportrol set to about 8oz max. system usual runs on less than 2oz. My hypothesis is that the boiler is still trying to fill radiators with steam once they have filled and the individual traps closed and the boiler makes steam faster than the radiator can condense it back to water.
  • Koan
    Koan Member Posts: 439
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    Sorry - I see below that this is (or can be ) an issue. Using a B&J big mouth main vent, so it is not inadequate venting.