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question on dry returns

Joe VJoe V Member Posts: 233
I have a two pipe system with two mains and two dry returns. My question is. the dry returns come together near the boiler, should they connect above the water line, or below?


  • JStarJStar Member Posts: 2,668

    For two-pipe, either way is acceptable. No steam will be in the returns to create an imbalance.
    - Joe Starosielec
    [email protected]
  • Joe VJoe V Member Posts: 233
    maybe I'm confused

    my header splits into two loops along the outer perimeter of house, circle back to boiler and connect above the waterline, then drop below the waterline with a single pipe. their vents, vent until they get hot. The condensate has its own return. I think by connecting above the water line, the shorter loop vents first, then it's steam pushes into the other loops return. forcing that loops vent to close and trapping air between two heads of steam.
  • Double DDouble D Member Posts: 172
    edited March 2014
    Is yours 1 pipe?

    Joe, on a 1 pipe you need to drop them independently below the water line of the boiler with their own separate main vents. If yours is 2 pipe, you need to find out why steam is getting into the dry return. Ex: failed open radiator trap or failed open crossover trap.
  • Joe VJoe V Member Posts: 233
    edited March 2014
    I confused terminology -again

    Sorry! it is a two pipe system. what I want to ask is, should the two end of mains join above or below the waterline?

    What I am seeing is the short loop vents fast and closes its vent..

    Then,because the two end of mains join above the water line, steam crosses over to the longer loop,heats that vent until it closes and air is trapped in the longer main.

    I believe they should connect below the water line so they stay isolated. Am I right?
  • Double DDouble D Member Posts: 172
    Post some Pics

    Post some pictures of the piping you are talking about. Also take some pictures of the dry return and a radiator with its piping. Are the end of main vents the only vents on the system?
  • Jamie HallJamie Hall Member Posts: 6,694
    In two pipe steam

    it is not only the mains which need to be vented, when you think about it.  It is also the dry returns.  Why?  If they are not vented, then air can't get out of the radiators, no matter how good your main venting is.

    A fully looped steam main is very difficult to vent properly.  As you note, unless you are very fortunate indeed you will get air trapped somewhere in the loop.  For this reason, fully looped steam mains are just a little unusual.  Looped dry returns, on the other hand, are no problem -- since steam is never supposed to get into them in the first place.

    Your first post refers to the dry returns.  As has been said, there is no problem if they connect above the water line near the boiler.

    Later posts refer to the steam mains themselves.  If they connect above the water line, there is a problem.

    It needs to be perfectly, unambiguously  clear what we are talking about.

    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
  • Joe VJoe V Member Posts: 233
    Thanks Jamie

    And sorry about the confusion in original post.  This is not the first time I did this.

    The dry returns are vented. 

     I meant to say the end of mains and, if successful, attached a sketch of what I have.  One loop is approx 30% shorter than the other loop.  Hence, the half of the house served by the longer loop takes longer to vent.  What I was doing, after reading the many posts on venting, was timing how long it takes the steam to reach the end of mains without the vents installed.

    Naturally, the short loop vented first so I replaced that vent.  Then waited for the other loop, but what I saw happening was the steam crossed over to the other main because it is above the waterline.  I reinstalled that vent and it too closed.  So, that means air is trapped in the larger loop.  So, I was seeking confirmation that the conection should be below the NWL before I repiped it.
  • Joe VJoe V Member Posts: 233
    in conclusion....

    I never felt or detected a problem. I didnt even realize my end of mains were connected above the water line (but it was below the waterline of the original boiler).

    So I fixed it. the difference is now both loops heat faster (5 min &10 min)- Twice as fast.

    The vents dont huff & puff any more, they are silent. the water in sight guage went from a one inch bounce to a quarter inch bounce, and the pressure went from 9 oz to well, I dont know. the rads heated up at zero oz and I shut her down. it is 70 degrees outside after all!

    thanks for all the help over the years. I believe I treaded my last pipe on this system!
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