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Is the boiler to small?

First of all I am no steam expert. I am a distributor and was asked to size some boilers in a retail / office building. It is nothing big but my contractor is questioning me. He removed 2 old large steam boilers that were supplying a loads of of yesteryears. The building has had many upgrades in efficiency. Some radiators were removed and replaced with Renni's.  I have sized the replacement boiler based on the load of the radiators that remain. The main they connected to was a 4" or 6" (cant remember).  They did not change the main vents or the radiator vents. They also didnt insulate the main. I do admit that I didnt allow quite 33% piping loss allowance but at 45 degrees outside it should heat the building if the steam can get to the radiators. Is it possible that the large main from the old system could be causing the steam to condensate way to fast? Its only traveling 35-40 feet. My thought are;

Insulating the mains

New main Vents

New radiator vents.

They want to keep raising the pressure.  The pressure does not come up in the boiler nor does the boiler shut off.


  • Jamie Hall
    Jamie Hall Member Posts: 22,932

    the boiler is sized even close to the total EDR plus the pickup, you should be OK.  Is it that the system doesn't heat?  Doesn't heat evenly?  Or is someone just being worried?  The proof is in the pudding, as they say -- or in this case, in the radiators getting warm.  It isn't clear from your post as to whether you have a no heat problem or a worried contractor problem.

    Couple of things. That big main wouldn't cause a problem -- provided it is insulated.  Since it isn't insulated, it will.  In fact, it could be condensing most of the steam.  Get it insulated, the sooner the better.  There is good fiberglass insulation available for it; I'd use a 1" thickness.

    Second, as I'm sure you're aware from reading the Wall, raising the pressure won't help a bit.  In fact, it will make things worse.  It shouldn't ever be more than a pound and a half, and a pound will be even better.  Resist your contractor on that one.

    Third, make sure that there is adequate venting.  You're right on track on that one, and that big main will require a good big main vent.  Get the main insulated first, then see what happens.  If you need new main vents, Gorton's are fine -- but you may want two or three of them.  Get that fixed before you fiddle with the radiator vents (though if the system has ever been run over three pounds, they'll need replacing, too -- pretty well guaranteed) (the main vent is probably toast too, if the system has been run at too high a pressure).

    Keep us posted!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • vt_steam
    vt_steam Member Posts: 2
    I feel better

    I thought I was on the right track.

     Complaint #1;  some radiators get hot, others in the same room don't .

    Complaint #2; Changing the vents was not in the price so we didn't do it.

    Complaint #3; Sure is hot in the boiler room!


    My suggestions .

    Insulate those pipes!!

    Change the main vents.

    Change the Radiator vents.

    The contractor has pulled other subs on the job to evaluate it. None of them with experience. He called me because I did have some. We now have to many cooks in the kitchen.

    My biggest question from the post was if the big main could be condensing  my steam enough to starve the radiators. I only allowed, I think, about 20% on the piping allowance. My mistake but it shouldn't bother in this weather.

    It now sounds the contractor just doesn't want to put in a little extra to finish the job right. ( I stock vents and insulation)
  • Insulate + Vent the Main!

    That uninsulated big main is acting like a huge radiator. It needs to be insulated.  As to the main vents if the main doesn't have large capacity working vents, the air can't escape and  that will keep the steam getting to the radiators. The faster you get the air out of the mains, the faster`steam gets to the radiators. You can't have too much venting on your mains!  After you get steam to the radiators you can adjust the radiator venting as necessary to balance the system.

     You might want to buy for your contractor,  Dan's book "We Got Steam Heat" and "The Lost Art of Steam Heating available at the "Store " at the top of this page.  Easy reading that even a contractor could understand! :)
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