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hot cold water

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  • hot cold water

    In an older posting I discussed the re-plumbing of our home. We now have wirsbo-pex.

    The house is on a concrete slab so the pex was run via the attic. Here in Arizona the attic gets really hot! during a typical 110 degree F summer day the attic can exceed 140 degrees F.

    Now usually our cold tap water is warmer than the ambient temperature of Minnetonka Mn.
    but I have noticed the cold supply is often hotter than the hot water! I need to let it run a while to cool down to 80-85 degrees.

    I asked our plumber about wrapping the cold supply with that DYI foam insulation. You know, the split foam tubing for insulating pipes you find at home Depot. He said it would not make much difference but I think it can help a bit..

    Any ideas out there?

    Cactus Man

  • #2
    Re: hot cold water

    I would insulate it I guess, though if the pipe is on the outside of the house insulation it probably won't make a lot of difference. I think I'd be calling the plumber that did the work. 140 degree water can scald and could be a liability issue.


    • #3
      Re: hot cold water

      it will help for a couple of reasons.

      #1 it will help keep the u.v. rays from damaging the pex

      #2 insulation is designed to contain heat loss either from escaping or entering.

      sure if the cold is not used for extended periods, then the radiant heat will eventually enter the pipe warming it up. same goes for the hot line with heat escaping.

      buy good 1'' thick insulation, not the cheap diy stuff. we typically use 1'' thick fiberglass insulation for this. not the foam stuff.

      also is your attic properly vented and insulated? do you have any of that reflective foil type paper under the roof joist to bounce the heat back off from the roof?

      all else fails you can think about a recirc. system on the cold to keep the water moving and circulate into a non powered water heater tank. the tank acting as a large tempering storage tank.

      phoebe it is


      • #4
        Re: hot cold water

        thanks for your replies.
        I want to emphasize no pex is "outdoors" so I do not have any UV challenges.

        The attic is well insulated. I have a metal roof sitting 2" above the roof sheathing and there is a reflective membrane under the metal roof.

        I will plan to scurry up into the attic when the temperature drops to 100F..or early fall.
        I was actually considering two layers of the foam pipe insulation. for example,
        use the correct size to insulate the 3/4" run then cover that insulation with the next size that would fit.

        The run from the water meter is 1" pex 18"-24" below frost line here. then goes to copper as it rises to the house entry. Once inside it returns to pex 1" and runs through the attic to the manifold. All runs hot and cold are 3/4" from the manifold up into the attic
        to their assigned, bathroom etc. All pex runs are then terminated to copper 1/2" and connect to the various fixtures, shower, toilet, sink....

        The pex is running above the insulated attic and is secured to the studs..I really have not ventured up yet for a good look.

        Right now I'm investigating my insulation options and their value.

        Cactus Man


        • #5
          Re: hot cold water

          Insulating the pipe in the attic will help a little bit, but the simple fact is it gets really hot in the attic. We have the same problem in southern Nevada. In the summer, your cold water is not going to be that cold.


          • #6
            Re: hot cold water

            hi Nevada plumber..I think the word to describe our cold water in the summer
            is "TEPID"


            Cactus Man


            • #7
              Re: hot cold water


              I know this doesn't belong over here in the plumbing side but please think about this some. Where you are I'm sure your attic really gets it bad with solar heat when the sun shines.

              Install louvers that you can open (spring) and close (late fall) in one end of the attic and a thermostat controlled fan with automatic shutters in the other end. Be sure you have more than enough inlet area so you don't pull a vacuum in the attic when the fan is running. (2) little 14" Gable type fans really helps my attic. I was lucky to have windows in both ends. In the spring I open them up. Both ends of my roof overhang the end walls enough so rain isn't an issue. If it is you can get shutters for the fan and angled louvers for the inlet end. If you really want to go all out there are motorized louvers with an interlock switch for the fan. Until they are open there's no power to the fan motor.

              One way or another get the nasty heat out of your attic.

              The "Made In China" fans at the big box stores are POC. Get one made here in the USA from a building supply house or an electrical supply house. Broan makes several good ones.

              The little box is the thermostat and wiring box.


              To everyone that sees this, installing powered attic ventilation will lower the load on your AC. Over time you do save good $$$ on you electric power bills. The small fans don't take much power to run. Mine run from about 11am to midnight and then shuts off. On a rainy day they don't run at all. (set to start at 105F and stop at about 95F / about 5 feet off the floor)
              Last edited by Old Grunter; 08-04-2008, 07:47 PM.


              • #8
                Re: hot cold water

                Thanks Old Grunter..I have attic ventilation
                I have an attic fan on a thermostat but in summer it runs almost 24/7
                I have a large opening at the gable end and there is air movement but it's still hot and that's the way it is here in the desert. I have never had to worry about ice dams here ha ha.

                I'm confident that when I finally venture up into the attic and insulate [very well] the
                plumbing runs both hot and cold The problem will be resolved. I'm planning on double layers of insulation at a minimum and then I can have comfortable tepid cold water!

                Cactus Man


                • #9
                  Re: hot cold water

                  Post removed
                  Last edited by Old Grunter; 08-05-2008, 05:41 AM. Reason: I was being a S @$$ and that aint good


                  • #10
                    Re: hot cold water

                    Check into something called cool vests. They're a lighweight material that has pockets for frozen gel packs. Works very well. Also try to work in the attic at night. Another tip for the itchy insulatulation. Grab some pantyhose, ball it up and rub in one direction on your skin and it's take most of the insulation out.
                    Buy cheap, buy twice.