Pressure balance tub/showers & insta hot/on-demand systems don't work together well??

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by I love pizza, Apr 21, 2006.

  1. I love pizza

    I love pizza New Member

    Mar 22, 2006
    I'm curious what you folks have heard good and bad about pressure balanced tub/showers and insta hot/on demand hot water systems. I've heard stories lately that some insta hot or on demand systems make the hot pressure a little lower than it normally is and because of that any make of a tub/shower that has a pressure balancing spool will cause that spool to react to the imbalance of pressure on the hot side vs. cold side pressure causing a reduction in flow.

    What I'm getting at is I think pressure balancing has been around longer than these insta hot systems and now the old technology doesn't gel w/the new technology and a new issue has been created from this mix of technology. This is what I've heard, but have you run across similar scenarios?
  2. Master Plumber Mark

    Master Plumber Mark Master Plumber

    Feb 6, 2005
    Sensitivity trainer.. plumber of mens souls
    indianapolis indiana - land of the free, home of
    yes they dont work well with anything

    tankless will usually cause you some grief and

    you sepnd the next few years trying to "tweak it"

    hopeing to recoup your investment......

    its only normal when you got about a 1/2 inch or less
    coil for the ot side and a 3/4 cold full line fighting eash otehr through
    tha tpressure balanced valve.....

    then when the coil begins to lime up, its all over
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  4. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona

    They are pretty much about the same age. But if you select an undersized tankless heater, then the pressure loss at maximum flow will be "enormous" and the cold water flow will be diminished to match it.
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