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Thread: Bathtub water flow rate question

  1. #1
    DIY Junior Member texcollins's Avatar
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    Default Bathtub water flow rate question

    I need to put a faucet valve in my bathtub and have been presented with two choices, either a 14.9 GPM@45 PSI or a 7.2 GPM@45 PSI. Can anyone tell me what a standard bathtub flow rate is? There is about $150 difference between the two choices and I'm wondering the flow rate in a typical bathtub is so I might have an idea how to compare. Thanks!

  2. #2
    Plumber jimbo's Avatar
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    One question would be what size pipe you have feeding the tub, and at what length from the main/water heater. 1/2 inch pipe will not deliver 14 GPM, without way too much pressure drop. You would have a water velocity of 14 feet per minute ( way too much ) and a pressure drop of 22 psi in 40 feet.
    Last edited by jimbo; 03-22-2008 at 02:02 PM. Reason: add

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    As noted, the biggest thing is what size are your supply lines? My guess is that the higher flow rated one expects 3/4" supply lines, and you won't get that flow unless they are that big.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    Master Plumber Redwood's Avatar
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    The larger flow tub fillers are primarily for large tubs. Yes the supply would have to be there.

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