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water pressure acceptable range

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  • water pressure acceptable range

    I am not a Plumber.
    I have an old house [in Phoenix AZ terms] it was built around 1966
    "before building inspectors"! We acquired it in 1987.
    Sadly the house was built by a wood shop teacher and I won't bore you with all the horror stories! [for example he used interior grade sheathing for the roof deck!]

    My plumbing is Galvanized pipe [yuk]

    I dread the day I need to re-plumb the house ...........

    ok, here are my questions...........

    If I were to connect a water pressure gauge at the front of the house garden valve above the main shut off valve, what would the acceptable range of pressure be?

    If I then hook up an adaptor and measure the pressure at say the kitchen faucet what pressure value should I expect to read?

    I do acknowledge I have some flow limitations at some areas and I suspect it's due to the galvanized pipes being restricted. I did a repair and used CPVC with great success.

    When the time comes to re-plumb the house would pex be a good choice?
    The runs can go into the attic and fortunately the bathrooms are next to each other.

    I do not know if any supply runs are embedded in the concrete slab.
    I do believe though that I could get most of the runs via the attic and actually have minimal wall demolition.

    For now though, I'm interested in pressure values in a residential home.

    Thanks , and I did do a forum search but did not find answers to my questions

    Cactus Man

  • #2
    Re: water pressure acceptable range

    Your pressure is determined by the water supply. On a well and pressure tank system the pressure is set based on water the home owner needs for pressure and what the system is capable of. typical ranges are 30/50 and 40/60

    In your case I'm guessing you have city water. Cities tend to run higher pressure. Generaly the lowest pressure you see on city water is 40psi. I've seen pressures as high as 100psi. If your pressure exceeds 75psi it is recomended you install a pressure reducer.

    The pressure should be the same anywhere you check it.

    What will vary between locations is gallons per minute of flow. Which I think is what your actualy looking for. That you can measure with a stop watch and a 5 gallon bucket. You can compare results between the kitchen sink and the hose to determin how restrictive the plumbing may be.

    There is no strict standards of what your pressure and gallons per minute should be. The determining factors are: Does it meet 'your' needs? And. If it doesn't meet your desires how much effort are you willing to put into making it do so?

    On replumbing a house I wouldn't recomend anything other than copper.


    • #3
      Re: water pressure acceptable range

      boytyperanma (and that handle is difficult for a simple guy like me to write) is talking real sense here. This is a good explanation of the pressure vs. volume situation that arises in plumbing.

      The only thing that I would add is that the volume necessary does not have to be based on "does it meet your needs". There are basic formulas, included in most plumbing codes, that can be calculated with little effort.

      I'm sure that there will now be posts from a few plumbers on this forum who will say that we are over complicating the issue, so let it flow.

      Your post was good.
      the dog


      • #4
        Re: water pressure acceptable range

        as noted earlier. pressure to the building is measured at a static condition. nothing flowing. it doesn't matter if the line is a 1/4'' ice maker line or a 2'' water main. the static pressure will be the same. as you go up in elevation from floor to floor, the static pressure will drop off approx. 1/2 pound per foot of elevation.

        now when you start to run water and measure the drop off pressure and the residual pressure, size will matter. in your case the old gal pipe is where the restriction is and this is where you will see the drop off as the volume will decrease and the pressure will drop too.

        a pressure regulator is required when the pressure exceeds 80 psi.

        as far as material goes. if you 've had good luck with cpvc, great. pex is also a very good material, requiring some special tools, crimpers and typically certification. copper is also good, but spendy to buy. it also requires a knowledge of proper soldering.

        i would probably lean to cpvc in your case as you've already used it and doesn't require any real special tools. it's also pretty inexpensive and easy to use.

        Last edited by PLUMBER RICK; 01-20-2007, 02:25 AM. Reason: typo's
        phoebe it is


        • #5
          Re: water pressure acceptable range

          I know he is in AZ but given that I heard on the news recently that it snowed in Vegas how cold does it get where you are? If you run through the attic space will freezing be a concern in your area? If not what about the excessive heat that can build up in attic spaces? It may be hot enough to affect or limit your material choices. What would your water taste like after sitting in that plastic pipe or tubing all day at 120F? what chemicals will be dissolved or leach out from the piping at those temps? I know it can reach over 110F here in my attic, so I am betting that 120 is possible in AZ, heck it gets that hot outside at times does it not? I remember being in Death Valley in early October a couple years ago and it was 109F.

          Our code here in NJ (2006 NSPC which I know is used in only two or three states) has a minimum pressure requirement.

          From 2003 NSPC (I don't have a copy of 2006 yet as it was just adopted Jan 1, 2007);

          10.14.2.a ..."For design purposes, the required pressure with flow at each fixture inlet shall be 15 psig minimum for all fixtures, except 25 psig for blowout water closets and blowout urinals."...

          And it then goes on to specify the min flow rates for each type of fixture.

          10.14.4 states that if the pressure is not sufficient to meet the minimum flow requirements that a booster pump and pressure tank or other approved means must be used.

          But regardless of which code you are subject to, there is a relationship between pressure and delivered volume (GPM), which is a function of pressure and pipe size. You won't achieve the required minimum flow rates without sufficient pressure. Another reason for maintaining a minimum pressure is to help protect the water supply from contamination.
          "It's a table saw, do you know where your fingers are?" Bob D. 2006


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