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  1. #1
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    Default New plumbing, old house, lower pressure

    We recently had our plumbing replaced with PVC - the old copper pipes were prone to pinhole leaks. The copper pipe coming into the house is 1" and is still copper about 5 feet into the house after the shutoff valve (some of the original copper remains).
    At that point it was converted to 3/4" PVC plumbing into the rest of the house, with the branches into the fixtures being 1/2" (where we used to have 1/2" copper).

    Now, in most of the house, the pressure is slightly lower than before the conversion - is this because of the 1" -> 3/4" conversion near the source?

  2. #2
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    Default Re: New plumbing, old house, lower pressure

    I don't think you have PVC, it is not allowed inside, it is more then likely CPVC. The pressure difference could be because CPVC has a smaller inside diameter then copper. What you are experiencing is a volume difference.

    John

  3. #3
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    Default Re: New plumbing, old house, lower pressure

    Yea, probably CPVC. So with the outside diameter reduced from 1" (copper) to 3/4" (CPVC), the inside diameter would be even that much more reduced - that could make a large perceived difference in pressure ?


    Quote Originally Posted by johnjh2o View Post
    I don't think you have PVC, it is not allowed inside, it is more then likely CPVC. The pressure difference could be because CPVC has a smaller inside diameter then copper. What you are experiencing is a volume difference.

    John

  4. #4
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    Default Re: New plumbing, old house, lower pressure

    There will be a difference but it shouldn't be that noticeable. I would check to be sure the main valve is turning on all the way. If it is a gate valve the stem could be broken in a partly closed position.

    John

  5. #5
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    Default Re: New plumbing, old house, lower pressure

    Quote Originally Posted by rakes View Post
    The copper pipe coming into the house is 1" and is still copper about 5 feet into the house after the shutoff valve (some of the original copper remains).
    At that point it was converted to 3/4" PVC plumbing into the rest of the house, with the branches into the fixtures being 1/2" (where we used to have 1/2" copper).

    Now, in most of the house, the pressure is slightly lower than before the conversion - is this because of the 1" -> 3/4" conversion near the source?
    Where the PVC starts, what was the original size of the copper? The main coming to the house is always larger than what the house is plumbed with, so it is not unusual to see a size reduction after the main shut off at the house. If the main feeder throughout the house is 3/4" and then branches to 1/2" to feed fixtures, that is also normal, as this provides adequate volume to all areas, and the reduction maintains pressure at the point of use.

    My suspicion is that the supply was necked down at the water heater or water conditioner. Either of those would result in a significant difference in overall house pressure.


    Quote Originally Posted by johnjh2o View Post
    The pressure difference could be because CPVC has a smaller inside diameter then copper. What you are experiencing is a volume difference.

    John
    Pipe diameters are measured on the inside, or inner diameter (I.D. ), not the outside dimension, which means that a 1/2" pipe is a 1/2" inner diameter pipe, regardless of the material it's made of.
    I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!

  6. #6
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    Default Re: New plumbing, old house, lower pressure

    Quote Originally Posted by A. Spruce View Post
    Where the PVC starts, what was the original size of the copper? The main coming to the house is always larger than what the house is plumbed with, so it is not unusual to see a size reduction after the main shut off at the house. If the main feeder throughout the house is 3/4" and then branches to 1/2" to feed fixtures, that is also normal, as this provides adequate volume to all areas, and the reduction maintains pressure at the point of use.

    My suspicion is that the supply was necked down at the water heater or water conditioner. Either of those would result in a significant difference in overall house pressure.




    Pipe diameters are measured on the inside, or inner diameter (I.D. ), not the outside dimension, which means that a 1/2" pipe is a 1/2" inner diameter pipe, regardless of the material it's made of.

    The OD of 1/2" copper and 1/2" CPVC is 5/8", know com-pair the wall thickness of the two. You will see that CPVC has a much thicker wall thickness, making the ID smaller on the CPVC. This is also true on PEX pipe.
    John

  7. #7
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    Default Re: New plumbing, old house, lower pressure

    Quote Originally Posted by johnjh2o View Post
    The OD of 1/2" copper and 1/2" CPVC is 5/8", know com-pair the wall thickness of the two. You will see that CPVC has a much thicker wall thickness, making the ID smaller on the CPVC. This is also true on PEX pipe.
    John
    And you're saying that the scant fraction of an inch of that inner variance is enough to cause a noticeable difference in pressure? I think not.
    I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!

  8. #8
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    Default Re: New plumbing, old house, lower pressure

    Quote Originally Posted by A. Spruce View Post
    And you're saying that the scant fraction of an inch of that inner variance is enough to cause a noticeable difference in pressure? I think not.
    What I am saying is the ID of copper is not the same as CPVC. If you look at my 2nd post I stated that the difference in pressure shouldn't be that noticeable.

    John

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