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Using 3/8" Copper to save energy

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  • Using 3/8" Copper to save energy

    I did a partial re-pipe of my Grandmother's house back in the mid 1970's. This house was built in "around" 1925. It originally used all galvanized supply lines. When my Grandparents remodeled their 2nd floor bathroom in the early 1950's, the pipes were changed over to copper. The supply lines to the kitchen were also upgraded to copper durring a remodel, and at some point around 1960 a basement bathroom (reusing some of the 2nd floor fixtures) was built - again, using copper supply lines.

    The system originally used cistren water for some things, and city water for others. There were also several hot water heater systems over the years. This and the relocation of the 2nd floor bath created a somewhat bizzare galvanized piping system left in the basement that needed to be replaced as it became too plugged up to use.

    I had done a few copper connections before, but never a job this big. The local inspection office did not require a permit to be pulled because we were only replacing existing plumbing, but one of their inspectors did come out to check out the job before I started, and later to see how things went.

    Some of the "existing" copper piping, like drops or risers to existing fixtures, were run as 3/8 inch rigid copper. The inspector was very happy to see this, and encouraged us to continue the trend when we could. He explained that after the war (WWII) copper was expensive, and a lot of plumbers used 3/8 inch where 1/2 inch lines would now (1970's) be used. He suggested that we run individual 3/8 inch runs from fixtures for hot water all the way back to the water heater -- a run of up to 30 feet in some cases.

    He explained the smaller pipe would contain less volume and the smaller pipe sizes would permit the hot water to get to the fixtures faster than even 1/2 inch pipes could. He said this would be particularly helpful in a house with one occupant, where water lines might sit unused for a day or two. He also encouraged us to install individual valves on each hot water line as close as possible to the water tank, to facilitate future repairs or renovations.

    He said on the cold-water side, we should use what he called a tree trunk approach -- using a 3/4 inch main, then breaking off with 1/2 inch for 2 or 3 fixtures and 3/8 inch or 1/2 inch for single fixtures. He again suggested individual shut offs, but said they should be placed as close to the point where the "branches" joined into the 3/4 inch cold water trunk.

    Every hot water usage (main bath sink, main bath tub, kitchen sink, washing machine, basement bath sink, and basement bath shower) were run as individual 3/8 inch lines and were individually insulated. This took a little time to layout and a lot of pipe to build. We build a short 3/4 inch header above the hot water tank with 7 valves -- the spare for a future dishwasher.

    The results were impressive. Hot water at even the furthest tap took only a few seconds to get to the fixture, even after a weekend of no use. Since then, I have lived in several houses with 3/4 inch hot water headers about the same length, and it takes a lot longer to get hot water. I know that today recirculation pumps and other systems are used to give the "instant hot water" effect to far-away fixtures. My question is what was wrong with this method? I can't find any contemporary references to using this approach as a way to save on energy costs.

    At the time me and a friend did my Grandmother's house (which we were able to complete in two days), we were able to pick up 3/8" rigid in 10' and 20' lengths, along with the needed 1/2" and 3/4" sizes at the local plumbing supply house. Even then, the 3/8 inch stuff looked more tarnished, as if it had laying around quite a while. Today, I can't even find anyone who sells 3/8 inch copper pipe locally, and only a few places which sell 3/8 to 1/2 inch adapters.

    In retrospect, this seems to be a good approach to faster hot water delivery. Even at the time, the 3/8 inch pipe cost a little more than 1/2 inch simply because of the lower volume of 3/8 inch pipe which was sold.

    Today, I am faced with another galvanized upgrade. The local inspection department would permit me to install 3/8 inch rigid piping if I want, but I can't find a supplier. Any comments or suggestions would be appreciated.

  • #2
    Re: Using 3/8" Copper to save energy

    it's common if you go to an hvac supply house.

    pex is also an alternative in the smaller bore sizes.

    biggest issue is the demand. for a sink it's not an issue, but a tub or shower could be an issue for gpm.

    the manifolds are pre-made for pex and is a wise choice for the home run method of piping.

    rick.
    phoebe it is

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    • #3
      Re: Using 3/8" Copper to save energy

      That's interesting to hear. Sounds somewhat similar to how Pex systems are run today.

      I agree with Rick that 3/8" copper to a tub/shower valve may not be enough, particularly if it is a pressure balanced valve (though I don't think the smallest openings on a Moen valve are any bigger than 3/8")

      If you are soldering 3/8" copper be careful not to overheat the pipe or to use too much solder.

      If the solder runs inside the tube it could form an obstruction that could create turbulence or restrict the flow.

      Comment


      • #4
        Re: Using 3/8" Copper to save energy

        You still have to size according to your code.
        sigpic

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        • #5
          Re: Using 3/8" Copper to save energy

          Originally posted by Swade Plumbing View Post
          That's interesting to hear. Sounds somewhat similar to how Pex systems are run today.

          I agree with Rick that 3/8" copper to a tub/shower valve may not be enough, particularly if it is a pressure balanced valve (though I don't think the smallest openings on a Moen valve are any bigger than 3/8")

          If you are soldering 3/8" copper be careful not to overheat the pipe or to use too much solder.

          If the solder runs inside the tube it could form an obstruction that could create turbulence or restrict the flow.
          Explain why a pressure blanced tub/shower valve would make a difference if you used 3/8 i.d. coppa? I dont see it.

          Comment


          • #6
            Re: Using 3/8" Copper to save energy

            Originally posted by Swade Plumbing View Post
            That's interesting to hear. Sounds somewhat similar to how Pex systems are run today.

            I agree with Rick that 3/8" copper to a tub/shower valve may not be enough, particularly if it is a pressure balanced valve (though I don't think the smallest openings on a Moen valve are any bigger than 3/8")

            If you are soldering 3/8" copper be careful not to overheat the pipe or to use too much solder.

            If the solder runs inside the tube it could form an obstruction that could create turbulence or restrict the flow.
            Please explain why using 3/8 id coppa would make a difference particularly with a pressure balanced tub/shower valve. I'm not following you.

            Comment


            • #7
              Re: Using 3/8" Copper to save energy

              Above and beyond the code and practical issues, you should consider how doing this type of modification might affect the resale value of this property.
              Teach your kids about taxes..........eat 30 percent of their ice cream.

              Comment


              • #8
                Re: Using 3/8" Copper to save energy

                Originally posted by TheMaster View Post
                Explain why a pressure blanced tub/shower valve would make a difference if you used 3/8 i.d. coppa? I dont see it.

                Not enough volume

                Comment


                • #9
                  Re: Using 3/8" Copper to save energy

                  Originally posted by Swade Plumbing View Post
                  Not enough volume
                  Well thats wrong information. You would have enough volume if the pressure was the typical 60-80 psi and within a reasonable distance and a pro piped it.

                  Proof? Thats how pex home run manabloc type systems are installed with 3/8 i.d. pex with insert type fittings that reduce the I.d. even more.

                  If it will flow 2.5 gpm through the showerhead its enough water...Correct? Do you think one 3/8" i.d. line would put more than 2.5 gpm on the floor if it pulled completely out of a fitting? Thats 1/2 a 5 gal. bucket for those who need a reference.

                  Comment


                  • #10
                    Re: Using 3/8" Copper to save energy

                    3/8ths pex and 3/8ths copper have different ID's. That said, look at how many older trailers (ok mobile homes) were piped with 1/2" galvy and then a rats nest of 3/8 copper. I think it will probably be OK though pressure and volume will both be reduced. It may take an hour to fill a tub. Still, if it were mine I would be looking at PEX and running a modified manifold system. I'm not a big fan of manablock or home run systems because it's expensive and uses a lot of pipe. A modified manifold is more cost effective and holds volume and pressure better with less variation.
                    sigpic

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