What length of dead leg becomes a problem?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Rossn, Apr 28, 2021.

  1. Rossn

    Rossn Member

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    In my remodel, I will also be prepping for a future kitchen remodel. For 1/2", 3/4" and 1", cold and hot water, when does the length of a dead leg become a health risk?

    i.e. If I run a 6" stub of any size, is that potentially an issue? 2'?

    Is there a conventional way a plumber would handle this scenario?
     
  2. Sylvan

    Sylvan Still learning

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    plumbing - fire suppression - boiler inspector
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    New York
    Any more than 2 feet is called a dead-end used for a future BUT do not confuse this with a air chamber to prevent hydraulic shock
     
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  4. Rossn

    Rossn Member

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    Thanks, Sylvan - so < 2' is typically acceptable from a bacteria perspective? Let's say 1/2" copper.

    Is the air chamber you are referring to is a water hammer arrestor?
     
  5. Jeff H Young

    Jeff H Young In the Trades

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    an air chamber is like a water hammer arrestor but not quite as it has no moving parts and to call it a hammer arrestor would be a bad/ or improper description. So most of us in trade try to use the correct words . its just a vertical pipe with a cap on it. common years ago but not so much now.
    Never really heard the proper max length of a pipe before being considered dead leg
     
  6. Terry

    Terry Administrator Staff Member

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    I used to install air chambers for my Moen shower valves. No way were they really needed though for those. I never do that now.
    I do use hammer arrestors for
    dishwasher
    washer
    icemaker

    My air chambers were done with 3/4" copper 16" long. I was a nut about it.
     
  7. Jeff H Young

    Jeff H Young In the Trades

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    Yea overkill but it looks clean like they are trying also it gave a good place to block and strap it off in the screwed pipe days . arrestor or proper air chamber dishwasher , icemaker , and wash machine that's our code on a good system not really needed but that's the rules!
     
  8. Terry

    Terry Administrator Staff Member

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    A friend of mine was being awakened in the middle of the night by the icemaker making the pipes in the walls jump.
    I gave him a hammer arrestor for it, but being a Boeing engineer, he didn't bother to install it. Kept hearing banging pipes.
    Then his father-in-law from South Dakota visited him, a plumber and he installed it for him.
     
  9. Jeff H Young

    Jeff H Young In the Trades

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    water hammers gotta love em! no fixture is exempt from the cause . The best way to avoid a water hammer I think is to size piping properly , strap well, basic good workmanship. I don't put arrestors at every fixture though I've had 10 times more problems at lavs , w/c, and tubs or showers than ice makers. many of the water hammer problems I fixed were not a simple matter of installing an arrestor, and the install doesn't often fix it at all or gives marginal help. certainly worth a try in many instances though. I think of them as a cover up for a screw up. something is wrong and an arrestor covers it up.
    Definitely a good call on the icemaker on that job from afar Terry, easy to overlook that
     
  10. gsmith22

    gsmith22 Active Member

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    I have read that 2 times the diameter of the pipe is the longest dead leg you want - which isn't very long. At that short length, there will be some circulation of fluid through the dead leg because it isn't that far removed from the main flow. I'm sure you can go longer than that, but how long is anyone's guess. Moral of the story, keep it as short as possible.
     
  11. Jeff H Young

    Jeff H Young In the Trades

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    1/2 inch pipe can only have a dead leg 1 inch long ? I've roughed in whole bathrooms for future I guess that's a no no
     
  12. breplum

    breplum Member

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    Two different plumbing engineers told me six inches max.
     
  13. gsmith22

    gsmith22 Active Member

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    Central NJ
    Just repeating what I read. I think the 2xOD dead leg length was tested and found that there was never any "stuff" growing in the dead leg when it was that short. Probably because the fluid movement caused a vortex in the short dead leg and kept its condition similar to the main pipe. I'm guessing you could increase it and probably be fine in most cases but would depend on what was in the water, general velocities in pipe, and a whole bunch of other variables not even recognized. My general takeaway was keep it as small as practical and if you could get away with 2OD and not cause any issues then strive for it.
     
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  14. Jeff H Young

    Jeff H Young In the Trades

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    Agree gsmith22, shorter is better. I often put an extra stub out under kitchen sink (2 hot and 2 cold) not knowing if owner will add a r/o unit or insta hot. stubs on water main for irrigation . I guess I should give a second thought to these items haven't in past considered short stubs to have any negative consequence
     
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