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Thread: Water Lines - Increasing Pipe Size

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    DIY Member pensfan84's Avatar
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    Default Water Lines - Increasing Pipe Size

    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?

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    Plumber Cass's Avatar
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    changing size will not change pressure...why do you want to do that?

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    DIY Member pensfan84's Avatar
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    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?

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    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.

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    DIY Member ChuckS's Avatar
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    Quote Originally Posted by Cass View Post
    changing size will not change pressure...why do you want to do that?
    So he doesn't get the cold shower when someone flushes. So you can run two facets simultaneously.

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    One who lurks Basement_Lurker's Avatar
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    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.
    Broken promises don't upset me. I just think, why did they believe me? -Jack Handy


    www.blackbirdkitchenandbath.com

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    Forum Admin, Expert Plumber Terry's Avatar
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    Water pipe sizing

    You can't go wrong by going with bigger pipes.

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    Senior Robin Hood Guy Ian Gills's Avatar
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    Yes you can Terry.


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    Moderator & Master Plumber hj's Avatar
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    Default 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.

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    DIY Member pensfan84's Avatar
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    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?

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    I&C Engineer (mostly WWTP) Lakee911's Avatar
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    Quote Originally Posted by Terry View Post
    Water pipe sizing

    You can't go wrong by going with bigger pipes.
    Well, you can if you want hot water to arrive quickly and you have no recirculator....

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    Homeowner Thatguy's Avatar
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    Pressure loss depends on velocity, with more at higher velocity.

    http://www.engineeringtoolbox.com/pe...oss-d_619.html
    Cold water in plastic pipe,
    ID = 0.5", 4.8 GPM, 5 ft/sec, 8.8 psi drop per 100'

    for copper pipe,
    http://www.engineeringtoolbox.com/pr...pes-d_930.html

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    Forum Admin, Expert Plumber Terry's Avatar
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    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 by Terry; 11-05-2009 at 05:35 PM.

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    I&C Engineer (mostly WWTP) Lakee911's Avatar
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    Quote Originally Posted by Terry View Post
    Trying to suck water through a 1/2" straw and a pineapple shake.
    Well, that's my house....

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    Consultant cwhyu2's Avatar
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    aalina you know that you are repling to threads that are years old!

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