On a hot day our kitchen cold tap, if it hasn't been run for a while, will produce water at a temperature up to around 50-55 degrees C shortly after it is turned on. We haven't measured the exact temperature, but it's too hot to keep our hands in it.

Our house is only a few months old, so we had the plumber check the cause (in case the hot water pipes were too close, or similar) but the heat just appears to be from the ambient heat in the ceiling space, which the water pipes go through. I believe the plumber has since put some lagging around the pipe, but it hasn't prevented the problem.

Adding extra insulation around the pipe will obviously reduce the severity of the problem. What is the best type of insulation to use, and are there any techniques I can apply to get the best result? Is there anything else (within a sensible budget) that we can do?

  • Wow - People actually pay loads of money to have what you want to remove.- I would suggest running a new pipe.. not in the ceiling space.. Insulation will help.. but not eliminiate the problem.
    – Piotr Kula
    Commented Jan 25, 2012 at 11:02
  • 1
    The irony there is that we already have a solar hot water system installed! You can have too much of a good thing :-) Running a new pipe would be tricky unless it came in through the (brick) wall - we have a concrete floor. Thanks for your answer! Commented Jan 25, 2012 at 18:14
  • @ppumkin, no joke, I wish I had that setup! Our water supply is through the crawl space and it's insanely cold in the Winter! Commented Jan 25, 2012 at 20:15
  • I'm interested in knowing if the glass wool worked out for you. We have the same issue down here in Florida. We had copper pipes 20 yrs old go bad on us, so we had to repipe through the attic with some polymer piping and our cold water is getting extremely hot now that the Summer is approaching. It's not even here yet so it's worrying us. Please let me know if it worked out for you!
    – felipe
    Commented Jun 6, 2014 at 22:38
  • @user3550190, our house is pretty new so we had the builder's plumber come and try to fix it. I'm not actually sure what they wrapped the pipes with (the ceiling insulation is polyester), but it did reduce the severity of the problem. The water still gets moderately hot on a sunny day after a few hours without the tap being run, but it won't burn us now. Commented Jun 9, 2014 at 4:52

1 Answer 1


If you dont want to run a new pipe you will need specific insulation

enter image description here

Notice that this insulation has a shiny outside layer. This acts as a reflection for heat, and usually has a black/dark side on the inside.

The foam/glass wool used to wrap the pipe needs not be anything special, but I am sure there are special ones that locks out heat better.. instead of the conventional one that keeps heat in.. is there a difference? I am not sure.

Look at this insulation- They wrap silver around the pipe and then insulate it. You DONT want to do this.. because this keeps the heat INSIDE the pipe, and the insualtion slows down absorption of coldness form the earth

As commented- it has no difference--inside or outside- it will deflect the heat in both cases... This is open to debate though.

enter image description here

So you are looking for Glass Wool Pipe Insulation with reflective outer shield

enter image description here

  • 4
    There isn't a difference in placing the reflective insulation inside or outside the wool/foam. Insulation isn't intelligent; it doesn't know if it should keep something hot or keep it cool, it just insulates. When putting pipes in the ground you put the reflective layer inside the foam because it's more sensetive to tearing.
    – Guffa
    Commented Jan 25, 2012 at 15:40
  • Fair enough.. thats the difference between designers .. and builders.. practical and theory.. either way.. should work then. Thanks for comment, especially +1 sigh
    – Piotr Kula
    Commented Jan 25, 2012 at 16:02
  • @Guffa, I disagree with your comment regarding it not mattering whether the reflective side goes in or out (though I agree it "doesn't know" about heat or cold). Silver or pale colours insulate by reflecting heat (and by emitting less, if they're hot), but in many cases (such as metal foil) the layer will act as a conductor of heat if it's touching something. Having the black side out would make the silvered side less effective if it was touching the inner layer. At least that's my understanding of the physics of conductivity vs radiation. Commented Feb 2, 2012 at 2:20
  • @HighlyIrregular: I was talking about the reflective material going inside or outside the foam insulation.
    – Guffa
    Commented Feb 2, 2012 at 3:05
  • @Guffa, then I think I did misinterpret what you meant, but I believe the same principle applies. Anything touching the foil conducts heat through it, so the silvered side should touch as little as possible (ie so it should face outwards, when not underground). Commented Feb 2, 2012 at 9:14

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