Benefits from 3/4" Supply lines or a bad thing

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Rob Beaupre, Aug 12, 2009.

  1. Rob Beaupre

    Rob Beaupre New Member

    Hi everyone,

    Great forum! This is my first post here, but searched here a few times searching for answers to my questions.

    We are building a new house, and are at the plumbing rough in stage. The question I have is basically, will I benefit from running 3/4" copper supply lines to all fixtures, then reducing to 1/2" at the connections or in my case, might it be a bad thing.

    We are on a well that gives us approx 10 gpm on a Constant Pressure system. However, there is a bit of silt coming through so we have two 'canister/bag' filters, a softener and then an 'Ultrafiltration' system (I know!!!).

    With all that said, if I use 3/4" copper supply lines to all the fixtures/bathrooms, will there be any added benefit, or could this be detrimental (ie more volume but sacrafice pressure)

    I have been getting differing opinions.

    Hopefully this is enough information

  2. FloridaOrange

    FloridaOrange Plumbing Designer

    SW Florida
    For a given volume the pressure will go up when you reduce the pipe size. A "typical" house will have 3/4" hot and cold "trunk" lines with 1/2" branches to the bathrooms, kitchen, washing machine and hose bibbs. Having a 3/4" hot water line longer than you really need will mean having to clear out a larger volume of cooled down hot water to the end point before you get hot water.
  3. nhmaster

    nhmaster Master Plumber

    S. Maine
    I find that these days, there is no such thing as a typical house anymore. These questions can only be answered by doing the calculations based on SFU, distance, and pressure along with pipe material used. Anything else is a crap shoot.
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    New England
    The larger pipe would provide the flow, if you needed it (and you may not) without a pressure drop. Since you aren't paying for the water, except for the power to pump it, wasting some waiting for hot may not be an issue. The larger pipe will waste more water unless you recirculate. If it is, then plumb the house with a dedicated return line so you can (maybe later) add a recirculation system. If you are careful about the layout, you can get this to work without using a pump, but it's easier to add a pump. Lots of ways to control the pump - occupancy sensor, timer, demand switch, thermostat, and lots of companies that make systems.
  5. drick

    drick In the Trades

    Ahem, the correct technical term for 'crap shoot' is the waste pipe.

    Sorry I couldn't resist:D
  6. nhmaster

    nhmaster Master Plumber

    S. Maine
    When it's there, ya gotta take it :D
  7. johnjh2o1

    johnjh2o1 Plumbing Contractor for 49 years

    The old rule of thumb is don't put two fixtures on 1/2". There are exceptions to this, like showers with more then one head or large tubs with 3/4" tapings on the faucets. Most codes are based on this.

  8. Terry

    Terry Administrator Staff Member

    Bothell, Washington
    I believe that was only two fixtures on 1/2"
    If you have a kitchen sink 40 feet from anything else, it would take a long time to clear the line, and you are feeding it with a 3/8" supply.
    It would make no sense to run 3/4" to it.

    In the Seattle area, many homes are required to have a 1-1/4" water service.

    A plumber would take out his code book and add the values based on pressure and distance.

  9. hj

    hj Moderator & Master Plumber Staff Member

    Cave Creek, Arizona

    The thing that determines the water line size is the faucet it is connected to. Very few faucets will benefit from a 3/4" inch supply line, but there are no bad consequences, other than the cost, of doing it.
  10. Gary Swart

    Gary Swart In the Trades

    Yakima WA
    As pointed out already, a 3/4" pipe holds much more water than a 1/2" pipe, so the time and water wasted purging a 3/4" hot water line of cold water can be considerable if the length of pipe is very long at all. Even with 1/2" pipe, a recirculating pump is a great innovation as you have virtually instant hot water at any outlet and at any time.
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