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dropped header size


We replaced our one pip boiler six years ago. I asked the installers to use a dropped header. The did but only used on riser (which the installation instructions said was an option) but they reduced the header from 2 1/2 to 2". The system works quite well, but this smaller header has always bothered me. I'm ready to change it out - how much of a difference would it make if I used 2 1/2 OR 3" pipe for the header?

I've posted a pic of the near the boiler piping. This was taken when it was installed and now all this piping is covered in insulation.

Any thoughts would be appreciated.


  • kevin_58
    kevin_58 Member Posts: 61
    drop header

    What size boiler is it? I would be more concerned about the bull head tee on the back main, and that they put the boiler in sideways, The controls are facing the wall making it harder to service and even check the water level.
  • Jeff_44
    Jeff_44 Member Posts: 94
    It's a

    Dunkirk PVSB 4 - 283 EDR. The main with the bull headed T services 4 rads. On the left of the bullheaded T is a small rad with 17 EDR. There is a way to tie into the end of this main and cap off the T. If I did this, what would be the effect?
    ALIGA Member Posts: 194

    eliminate the bull tee with the addition of another tee on the header, and two 90 elbows on the main.

    also insulate the near boiler piping.
  • Rod
    Rod Posts: 2,067
    edited September 2013
    Piping Changes?

    Hi Jeff- While from a design standpoint you would benefit from:

    1, a larger header (The "thumb rule" is that it should be a pipe size larger than the riser(s) coming out of the boiler.)

    2. by utilizing the second boiler riser port

     I personally would question how much (if any) increase in efficiency you would get. If you had a shorter boiler riser(s) I would say "go ahead and change it". However it would appear to me that your present "super tall" boiler riser has to be a huge benefit which probably goes a long way to make up for the other shortcomings in the near boiler piping.

    If you're not having a problem with wet steam and the system seems to be operating properly, I'd just wait to the next boiler replacement before changing the piping. As for the bullheaded tee- Since there is only one radiator on that one branch and if it's working okay, I'd just leave things alone.

    I'm just a homeowner so my experience is rather limited. Maybe one of the pros will comment and I would go with their recommendation if they think you would get a substantial improvement by changing the piping.

    - Rod
  • Hap_Hazzard
    Hap_Hazzard Member Posts: 2,849
    Boiler Riser

    The benefit of having a tall boiler riser is that carryover can't ascend higher than 24". The only thing better than this would be two tall boiler risers, which would cut the velocity by half, allowing even smaller droplets to coalesce and fall back.
    Just another DIYer | King of Prussia, PA
    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24
  • Jeff_44
    Jeff_44 Member Posts: 94
    Thanks for your help

    So the tall riser is helpful - but there should be two. What if I kept the single riser but added a larger header (say 3") - what would be the effect?
  • Rod
    Rod Posts: 2,067
    edited September 2013
    Boiler Piping

    Hi Jeff-  If you do decide to change the header, it would be worth using the other boiler port and adding a second boiler riser. As Hap mentioned, this cuts the exit velocity of the escaping steam in half. Ideally you would use a 3 inch header pipe. (one pipe size larger than the 2 1/2 inch boiler risers)  Keep the boiler riser height the same as what you have now.  You have to keep in mind that the boiler manufacturer's installation instructions are minimums rather than optimums.

        I've attached a great photo of Noel Murdough's glass boiler. Note the height of the water in the boiler risers. You can also see how the water separates out in the header pipe. The steam produced is nice and dry.

    - Rod
  • nolamike
    nolamike Member Posts: 9
    Steam velocity

    im new at this but here it goes.

    If you have a load of 283 edr thst equals 70.75 lbs condensate/ hr x 24 (cubic ft per pound at 2 psi

    Divided by 3.36 (internal sq/in of 2" pipe) x 25

    = 10.06 feet per second

    at 0 psi = 11.32 fps

    Here's the formula

    Lbs./hr x cubic volume steam


    25x internal area of pipe

    Around 15 is good so I'd say your just fine .

    Don't feel bad , I have a 1 mil btu boiler that someone installer with a 2" riser and no header at all.
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