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Drop Header Sizing......

ctjomacctjomac Member Posts: 52
I've read The LAOSH and We've Got Steam~! Great books, but I can't find the answer to this: We are replacing out 1953 boiler as soon as I can shut down for a few days this spring. I have it set up and pre-piping as much as I can, We have Double 2" horizontal mains with 388 edr attached: The old and new boiler have double 2" risers out of the boiler.

Why and what is the reasoning for everyone bumping the size up to 3" ? Is it well worth my time to do this?

Thanks Much Joe


  • crash2009crash2009 Member Posts: 1,484
    Forget about the old boiler

      Look in the manual for the new boiler.  The new boiler will tell you what it wants.

    By the way what is the model number of the new boiler?  And how about a couple pictures of the old one and the pipes (above and below)?
  • Jamie HallJamie Hall Member Posts: 6,693
    crash is right --

    check the new boiler's piping specifications.  But do remember that they are a minimum; if they say 2" for the drop header, that should work but it is the minimum.  Going up to 3" is more work, granted, but it will result in slightly better steam quality due to the lower velocity in the header.  Is it worth the effort?  Ah... I dunno.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • ctjomacctjomac Member Posts: 52
    Look and "When changing out and old boiler

    on my post from 1/9/2012....I am replacing with a Burnham MegaSteam 396 ...I have 388 sq. ft. steam. The in place boiler header wasn't installed correctly in my opinion...Right now the Burnham shows a 2" drop header in the manual...Dan's book says to up it one size and most people here seem to, but I don't understand what it would do for me. Both mains run about 25-28 feet to the last riser then return. THANKS ~!
  • ctjomacctjomac Member Posts: 52
    Jamie...does it do something...

    to lower the pressure?
  • AbracadabraAbracadabra Member Posts: 1,939
    pressure not velocity

    You increase the header to lower the exit velocity of the steam.  High velocity steam will pull water with it giving you wet steam (bad) vs. dry steam (good).
  • crash2009crash2009 Member Posts: 1,484
    oversized drop header

    Sorry about that, I didn't realize that you had discussed the first half of the project in another post.  Ok, so you are coming out of the boiler with 2", then dropping into the header.  Are you looking for the advantages and disadvantages of using an oversized drop header?

    It's a good, better, best thing.  Good that you have a header.  Better that you have a header that is dropped.  Best is that the dropheader be oversized.  Plus it looks real cool.  For me, better is good enough.  
  • Jamie HallJamie Hall Member Posts: 6,693
    The simple answer...

    is no, it doesn't change the pressure at all.  And, in fact, in the section of the header from the second riser to the first main takeoff, it doesn't change the velocity either (2 2" pipes have almost the same area as 1 3" pipe).

    But as crash says, it sure looks cool... !

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • gerry gillgerry gill Member Posts: 2,668
    an oversized header is

    a wide space in the road for the steam to better separate from the water that also got drawn out of the boiler..manuals provide the MINIMUM sizes that will work..since the header is now the steam separator, bigger is better..if you want to really get old school, the old timers would size the header to aggregate cross sectional area of the takeoffs from the header plus one size..(believe that's from the 1935 Hoffman data book if memory serves)..that's a huge header..that would give you a 3.5'' header..a seldom found pipe size today.

    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

  • RodRod Posts: 2,067

    Hi - Attached is a chart showing a comparison of the cross section of different sized pipes.

    If you put two 2 inch pipes into a 2 inch header you will increase the velocity. A 3 inch pipe has 3.06 times the cross section of a 2 inch pipe so even with two 2 inch pipes connected to it the velocity will decrease which will allow more water droplets to precipitate out which results in dryer steam. Dryer steam equals more efficiency.  As Crash mentioned it is a good, better, best sort of thing.

    You can learn a lot studying the dropheaders done by Gerry Gill and his crew, their dropheaders are works of art.

    - Rod
  • ctjomacctjomac Member Posts: 52
    I Undertand It Much Better Now...

    This place is SO COL....Thank You All for explaining it in a way that I can understand~!!!!!!...I'm going to go with the 3" piped Header to help keep the water down in the boiler area and only let the dry steam go up~!!!!!!! WOHOOOO

    I truely appreicate it and I'm sure I'll be back with more questions :)
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