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Why does hot water get colder right before it gets hot?

  1. Nov 9, 2005 #1
    I'm not sure if this is in the right section but here it goes.
    Ok for the sake of this question let's assume that the water hasn't run for a few hours
    Whenever I first turn on the hot water, the water first runs either cold or room temperature (depending on the amount of time since the last use of course) then RIGHT before it turns hot it gets a little colder than it had been seconds before, no matter how cold it was running before
    Is this a physics question or simply a plumbing question? :uhh:
  2. jcsd
  3. Nov 9, 2005 #2


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    Staff: Mentor

    It's a plumbing question, and it depends on the routing of the piping (ie, through the ground=cold, through your house=cool). For a typical house with a basement, the water at the tap will start at room temperature and the little bit of water that is in the pipes in the basement will be a few degrees cooler.
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