Water pressure and supply line question

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by Mike_B, Oct 11, 2006.

  1. Mike_B

    Mike_B New Member

    Messages:
    12
    Hello! I'm adding a shower and the fixture recommends 3/4" supply lines. The city line comes in at 3/4" and then it is reduced before the water heater. If I change it to 3/4" all the way up to the bathroom, can I "T"-off to the existing 1/2" lines to the kitchen, 1st floor bathroom, laundry, etc. How would this effect the water pressure throughout the house?
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,491
    Location:
    Cave Creek, Arizona
    pressure

    The dynamic pressure, which is what you are asking about, would depend on many more factors than just the size of the pipe. The distance from the largest water source, the amound of water flowing at the time, where it is flowing, etc., all determine what the pressure will be. When no water is being used, the pressure is equal everywhere in the house.
  3. Mike_B

    Mike_B New Member

    Messages:
    12
    Thanks HJ. So now I guess this becomes a volume question.
    With the shower fixture needing 3/4" for volume of water, do I need to run it before reductions to 1/2"?

    If I change it to 3/4" all the way up to the bathroom, can I "T"-off to the existing 1/2" lines to the kitchen, 1st floor bathroom, laundry, etc.

    The washing machines seems to start running when I take showers;) If
    I run 3/4" to the washing machine, will it make a difference or just leave it 1/2"?

    I want to be as effective as I can while I have access.
    Any help will be appreciated!!
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,899
    Location:
    New England
    3/4" pipe has 2.25x the volume of a 1/2" pipe. So, by running the 3/4" stuff to the high volume users, you've got much more available volume with the slightly larger lines. You'd be much less likely to notice a big drop in pressure with the larger line as long as you don't try to exceed the supply.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,491
    Location:
    Cave Creek, Arizona
    pipe

    You cannot use any more water than the valve or faucet will supply, regardless of how large the pipe feeding it is. Run 3/4" to the shower and branch off 1/2" as needed. The shower valve should compensate for any minor pressure variations. If there are major pressure variations, then the water supply source is inadequate.
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