Water Lines - Increasing Pipe Size

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by pensfan84, Nov 4, 2009.

  1. pensfan84

    pensfan84 New Member

    Messages:
    32
    Location:
    Pittsburgh, PA
    The water line coming off of my main shutoff is 1/2" - am I able to increase the pipe to a larger size right after the main shutoff without losing much pressure?
  2. Cass

    Cass Plumber

    Messages:
    5,980
    Location:
    Ohio
    changing size will not change pressure...why do you want to do that?
  3. pensfan84

    pensfan84 New Member

    Messages:
    32
    Location:
    Pittsburgh, PA
    Well...I'm installing a new bathroom on the second floor and the house currently has 1/2" throughout - it's old and starting to get deposits in spots and causing problems with pressure.

    Also, I looked at the main shutoff a little closer and saw that it's actually 1" coming into the house and has a threaded reducer to 1/2". I can simply replace the fitting.

    I'm trying to prevent the water temperature from changing in the shower when someone flushes the toilet, and a few master plumbers I've spoken to advised me that putting in larger water lines and then install 1/2" takeoffs for each fixture - is this not the case?
  4. BRD

    BRD New Member

    Messages:
    53
    Location:
    northeast
    A larger pipe size will have less pressure loss due to friction than a smaller pipe at the same flow. Therefore you will have more pressure available to your fixtures with a larger pipe. Your static pressure will remain the same. I'm not a plumber , so I don't know if this will help ypur problem with the toilets.
  5. ChuckS

    ChuckS New Member

    Messages:
    96
    Location:
    Aurora, CO
    So he doesn't get the cold shower when someone flushes. So you can run two facets simultaneously.
  6. Basement_Lurker

    Basement_Lurker One who lurks

    Messages:
    668
    Location:
    Victoria, BC
    Temperature fluctuations in your shower are only going to be solved once and for all by upgrading your shower valve to at least a pressure balanced unit...are you sure you were talking to master plumbers?

    Upsizing your lines will definitely allow for more water on demand if you have a big household and tend to run a few fixtures at the same time.
  7. Terry

    Terry Administrator Staff Member

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  8. Ian Gills

    Ian Gills Senior Robin Hood Guy

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    Yes you can Terry.

    [​IMG]
  9. hj

    hj Moderator & Master Plumber Staff Member

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    Location:
    Cave Creek, Arizona
    pipe size

    Increasing the pipe size will just insure that whatever amount of water is available at the point of increase will arrive at the faucet. ANY restriction ahead of that point will still affect volume, and thus pressure, in the new section. If this is a new tub/shower installation, you MUST use pressure balanced valves and these will automatically control the situation when someone flushes the toilet.
  10. pensfan84

    pensfan84 New Member

    Messages:
    32
    Location:
    Pittsburgh, PA
    Terry,

    Based off of the link you gave me, I fit into the 1' per branch category.

    would you then recommend 1" to supply the main branch, then each area (e.g. kitchens, bathrooms, laundry area) be reduced to 3/4", and then again to 1/2" for each fixture? or what way would you recommend?
  11. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Messages:
    1,328
    Location:
    Columbus, OH
    Well, you can if you want hot water to arrive quickly and you have no recirculator....
  12. Thatguy

    Thatguy Homeowner

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    1,459
    Location:
    MD
  13. Terry

    Terry Administrator Staff Member

    Messages:
    15,294
    Location:
    Bothell, Washington
    What most plumbers do, is work the chart backwards, and increase pipe size on the way back to the street.

    So for instance, if you need 1/2" pipe to two plumbing fixtures, like a tub and lav, then you would increase to 3/4" when you get to the third fixture.
    After a while, you will be adding more fixtures, and at some point you will be at 1"
    It doesn't hurt cold to be too large, but most plumbers keep to the chart for hot water.
    But even oversizing would be better then running a three bath home in 1/2" like your was.
    The last time I saw that?
    It was a house being "flipped" by carpenters for resale.
    The home sold for over $500K and had no water anywhere.
    Trying to suck water through a 1/2" straw and a pineapple shake.

    Most plumbers will run 1/2" hot for lav and tub, and 3/4" cold to the bathroom, splitting down to 1/2" for the individual fixtures.
    At some point, you're at 1" for the main branch.
    Last edited: Nov 5, 2009
  14. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Messages:
    1,328
    Location:
    Columbus, OH
    Well, that's my house.... :)
  15. cwhyu2

    cwhyu2 Consultant

    Messages:
    1,348
    Location:
    Cincinnati OH
    aalina you know that you are repling to threads that are years old!
  16. bluebinky

    bluebinky Member

    Messages:
    408
    Location:
    Santa Clara, CA
    Larger pipes reducing pressure is an old wives tale.

    Like others have said -- if done correctly, larger pipes should help, and a better shower valve will also help.

    Another thing that can help is to take-off for the toilets from a point before the split between hot and cold.
  17. Winslow

    Winslow Plumber

    Messages:
    450
    Location:
    Hawaii
    Increasing the size of the line will decrease friction loss not pressure, aside from greatly increasing volume.
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