Copper supply line question

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Nick_A, Jul 5, 2021.

  1. Nick_A

    Nick_A New Member

    Joined:
    May 19, 2021
    Location:
    Iowa
    Hello
    We are wondering if we can get some help sizing the supply lines for our addition. We have 1-1/2" CPVC coming into the house, and we plan to use copper from there. We are feeding 2 toilets, 4 lavs, 1 tub/shower, 1 shower with 2 heads, and 1 washer. These are all on the second floor. We are working on checking the pressure, but haven't run to town yet to get the supplies. We are out in the country tho on rural water so its nothing very high... Currently, our water heater has 3/4" if that is a factor. Farthest fixture away is the washer and it is ~60ft from the supply and water heater.

    What size would you suggest for the supply lines up to the second floor? We were looking at this link (https://terrylove.com/watersize.htm) at thought maybe we would want to run 1" up to the second floor and then run a main branch in 3/4 with individual 1/2 lines to each fixture? Or is the 1" overkill, or on the other hand, should the main branch line be 1" for awhile til we get past some fixtures?

    Thanks for any help - this forum has been great for us and we really appreciate it!
     
  2. Jeff H Young

    Jeff H Young In the Trades

    Joined:
    Feb 27, 2020
    Location:
    92346
    I'd say 1 inch with a 3/4 branch to w/h continue 1 inch on cold main to first branch then 3/4 to second bathroom run to washer could be 1/2 or 3/4 likely 1/2 if pressure not too low
     
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    The Copper Institute has a free handbook on their website that has the pressure and volume chart information you need to do this.

    You need to decide what your maximum pressure drop you can live with at what volume, then it becomes fairly easy to decide what is necessary to achieve that. Just general info, the longer the pipe, the smaller the ID, the faster you try to flow it (volume), the more pressure drop you'll get which can also start to limit volume available.

    They also have suggested maximum velocity of the water in the pipes that differ based on whether it's hot or cold. On hot, it's 5fps, on cold, it's 8fps. Exceeding those values cause three things:
    - literally eroding the inside of the pipe
    - water flow noises
    - excessive pressure/volume changes

    FWIW, on hot, a 1/2" copper line at 5fps is only 4gpm, but increases to 8gpm with a 3/4" line.

    A long run will also mean it will take longer to flush the room temperature water out to get the hot there, so you might want to consider planning for hot water circulation in your layout. Done right (insulated pipes required now per code), and on a timer, it can save not only water, but energy as well.
     
  5. Jeff H Young

    Jeff H Young In the Trades

    Joined:
    Feb 27, 2020
    Location:
    92346
    circ systems are real nice for instant or quicker hot water, of course almost no one puts them in due to cost the luxury and convenience vs cost seem a bargain to me and 60 foot to washer is on the long side .
    By all means read books and C.D.A . don't know how that applies to PEX . but I don't run 1/2 inch to a water heater nor am I running 1 inch or bigger on a 2 bath house. unless you have some really low pressure , I'd see no reason to run 3/4 or bigger to a toilet or Lav either. 60 foot run to wash machine your running PEX ok run 3/4 no biggie but not running 1 inch there either. the area to think about are the tub and the shower with 2 heads You don't want all that coming off a 1/2 inch line If its a huge tub might want 3/4 to valve depending on valve . if the tub and shower are close to manifold likely a home runs of 1/2 inch will be good.
    I'm not much of crunching numbers on this I used to 30 years ago but have worked my way into smaller jobs where I can pretty much figure smaller stuff like this without referring to fixture units or FPS. but those are very important if you are shooting for the minimum sizes with out going too small. Since I don't have a drawing I can't draw up sizing but just a general idea
     
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    Look at recirculation as the chance to save water and improve convenience. On that say 60' line, if you abide by the copper institute's recommendations of a max of 5fps, assuming the line has cooled off, it will take 12-seconds to flush that line out of the cool water, then probably another minute or more to warm the pipe up so you get close to the WH outlet temperature, and that's if you've insulated it well. Say you're using a vanity sink to wash your hands versus the tub or shower when you might want that full flow, it can easily take MUCH longer, as that faucet is flow restricted. So, let's round that off to 2-minutes to get fully hot water at 4gpm with a 1/2" line, and that would be 8-gallons, or with a 3/4" line, 16-gallons you may just run down the drain before you get fully hot water and, you had to wait for it...

    With a recirculation system, if I use mine as an example, within 5-seconds, I've got full hot if the system's timer is on, but it can take over a minute without (my line isn't as long as yours). Depending on how often you use hot, the line may cool off to ambient in between uses, so if you wanted at least warm to wash your hands, you could be wasting a bunch of time AND water. Even if you have a well, you're paying to pump that water out of the ground, and either filling your septic tank, or paying for sewer charges for water you really didn't use.

    If you've insulated the supply and return lines (required by today's codes), and you only run the recirculation during time(s) of intended use, depending on your utility costs, it can often be cheaper to use one versus not, and you'll always be saving water, which, depending on where you live, can be the bigger issue.

    Keep in mind that when flushing the line with that cooled off room temperature water, you're putting cool water into your WH, decreasing the maximum amount of hot available, too. If you had say a 40-gallon WH, and needed 16-gallons to flush the lines to be hot, you've essentially depleted your tank by half its useful volume! With recirculation, you have the full tank AND supply line from it, nearly doubling your available hot water you can use that first time in the morning.
     
    Jeff H Young likes this.
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