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Undersized Main Vent causing startup bangs?

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matthewb84
matthewb84 Member Posts: 27
edited October 2018 in THE MAIN WALL
Hi Everyone,

Quick question, I did some searching but can't find the exact answer on the forum. If I missed it, sorry for the redundancy.

I ironed out most of the kinks in my system but I am still getting banging at startup - lasts about 2-4 minutes starting a few minutes after the system kicks on.

Once it's over its pretty much done making noise.

Do you think this is water build up or is the main vent not flowing enough air? From what I can see everything is pitched correctly.



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  • Jamie Hall
    Jamie Hall Member Posts: 23,650
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    Somewhere out there... there is a low spot which is collecting condensate from when the pipes are first warming up and swooshing it into something. It's going to take some looking -- and may be just a sag rather than a real pie in the face low spot.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • KC_Jones
    KC_Jones Member Posts: 5,750
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    Are you positive it isn't expansion noise? That can make a sort of banging noise.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
    1Matthias
  • 1Matthias
    1Matthias Member Posts: 148
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    I've had systems that water hammered to high heaven on startup quiet right out with the addition of proper venting. Most likely, the root cause is still a sag in a pipe, but it did seem to help.
  • Fred
    Fred Member Posts: 8,542
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    If it Bangs, There is a pool of water out there somewhere. Slow vents don't cause banging.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,839
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    What @Fred, & @jamie hall are correct. @KC-Jones makes a good point
  • matthewb84
    matthewb84 Member Posts: 27
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    I am guessing something is pooling, I will take out the laser level again. Is there a way to determine expansion vs water noise?

    would water hammer/bang happen after everything has heated up?
  • Jamie Hall
    Jamie Hall Member Posts: 23,650
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    I am guessing something is pooling, I will take out the laser level again. Is there a way to determine expansion vs water noise?

    would water hammer/bang happen after everything has heated up?

    Be sure when you are using the level that you check the entire length of every pipe. It is quite possible for their to be enough sag in the middle of a longish run to produce rather spectacular bangs, even if the pitch between ends is correct.

    Expansion vs. water noise -- can be difficult to distinguish, but expansion usually is more or a repetitive noise (although it can be one almighty bang) and regular and frequent, also more musical and not as loud, while water hammer tends to be less regular and more like someone hitting the pipe. But it can be hard to tell.

    If it is indeed a problem with a sag type of pooling, it tends to go away once the pipe in question has heated up. Unhappily, expansion noises also go away once the pipe has heated up...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England