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2 boiler staged steam system

Dirk Member Posts: 4
I have existing 750,000 btu 1-pipe steam boiler needing replacement.I'd like to set up 2 smaller pkg'd boilers & stage them on outdoor reset.Are controls available for this for steam?I,d appreciate some feedback as I can't find anyone who has tried it.


  • Outdoor reset, huh?

    What temperature steam are you planning to reset to?

    I can help, I'm only trying to understand what you want to do....

    If you are trying to drop off one boiler in mild weather, it might not be two boilers of equal size, as one would be two small for the load. It might be a big and a small, or more than two.

  • Dirk
    Dirk Member Posts: 4
    2 boiler staged steam

    yes Noel I'm trying to stage the boilers for mild weather.That's the "outdoor reset" I'm considering. Trying to avoid overheating at the beginning & end of the season,as well as some fuel savings.Any thoughts on this would be appreciated.
  • check these




    If you have two pipe radiators, the load can be varied infinately. If you have one pipe radiators, you need to have enough boiler power still online to heat ALL of the radiation, after one boiler shuts down, or it will be right back on immediately.

    I'd count up the radiation, to see what the minimum is, use two or three boilers to meet this number, and the last boiler is sized for the pick-up and piping factor, which you can shut off as the pressure climbs off zero.

    If you want to use two boilers, I'd make one big enough for only the radiator load, and another boiler half that size to get you up to temperature.

    With three equal boilers, you can temporarily heat with two if the third one goes down (but expensively) and it won't matter which one goes down.

    With two pipe, you may find that only one will carry the load in mild weather, AFTER the mains get hot. This is because some radiators can, and usually will, get throttled back a little at the hand valve.

    That won't happen on one pipers.

  • Al Letellier
    Al Letellier Member Posts: 781
    staging steam

    Not much luck there. One boiler will meet the load. Two boilers of smaller size won't make enough steam to fill the system with one off. Look at Heattimer controls.They make an excellent "cycling" control. You can't reset steam as it still and always will take 212* to make it. A cycling control will start and stop the boiler in cycles based on outdoor temp. Say at design temp the boiler cycles off the pressure switch all day. On a milder day, the control says that the boiler only needs to run a percentage of the time in each set cycle time ( say at 40* the boiler only needs to run 18 mins out of every 30 minute cycle...just an example). Use one full size boiler and a cycle control, or better yet, two full sized boilers with cycle and lead-lag control for full redundancy. It's the best and safest way to control the boilers in my book.

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  • frank_25
    frank_25 Member Posts: 202

    Maybe you are thinking of a lead/lag system whereby two boilers light off and raise pressure, then one shuts down allowing the lag boiler to maintain pressure. This works fine when used in LARGE applications when properly piped with all the bells and whistles, but with a small load such as yours, I'm not totally sure it would work. Costly also what with the two boilers, and necessary feed tank w/pumps, etc. Me thinks you should look into a heat timer product as mentioned before.
  • Al

    Read this, about outdoor reset on steam....


  • Frank

    I realize that we just offered exactly opposite opinions to the gentleman.

    These work, and are an option in this case.


    A lot less money to buy, and to run, than what you suggest.

    Why is a tank automaticlly added? I didn't see any numbers that would indicate a tank to be added. Do you always add a tank before you do the math?

    If the returns are partly plugged and returning slowly, do you add a tank?

    My point is that a blanket approach gets the job done, the heat on, and the contractor down the road. Does that make it the best approach?


  • Boilerpro_3
    Boilerpro_3 Member Posts: 1,231
    Add TRV's

    > I have existing 750,000 btu 1-pipe steam boiler

    > needing replacement.I'd like to set up 2 smaller

    > pkg'd boilers & stage them on outdoor reset.Are

    > controls available for this for steam?I,d

    > appreciate some feedback as I can't find anyone

    > who has tried it.

  • Boilerpro_3
    Boilerpro_3 Member Posts: 1,231
    Add TRV's

    to the system. This would allow the load to lighten according to weather and should allow the boilers to stage off as you are thinking. Also, before doing anything, make sure you really need a 750,000 btu/hr boiler. I have pulled out several old steamer that were more thenm doulbe the size of what radiation and pirping needs where for the system. I have one right now about that size with only 260,000 btu/hr of radiation and a heating load of about 160,000.

    Do your math and homework carefully

  • ChrisL
    ChrisL Member Posts: 121
    Here's what you need

    Here is a link to a much better steam controller than the heat timer stuff. They're not cheap, but very good.


This discussion has been closed.