cold water supply lines in hot attic

A few months ago, I had a slab leak in the cold water supply to my kitchen sink. The plumber rerouted the line through the attic using PEX, insulated with a black foam sleeve/wrapper.
Now that summer is near, I am finding that, in the afternoon (if the sun is out and the outdoor temperature is in the 80s or above), the cold water from my kitchen sink tap is warm-to-hot for 30 seconds or more before it cools down. The kitchen tap is on the other side of the house from the cold water manifold, so it is a long run of pipe. I measured the temperature at the tap with a kitchen thermometer today-- it was 130 deg F for 10 seconds or so, which seems really out of line. I haven't seen this problem mentioned in other postings to this group concerning attic routing of water supply lines.
Is this normal for attic-routed cold water supply lines in a hot climate? I have a hard time believing that the water could pick up so much heat. My attic has passive ventilation, with no soffit vents. Would improving attic ventilation result in a big improvement? Or is the plumbing work defective somehow?
Thanks
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randyn wrote:

Hm - I'd say the black foam is absorbing ambient heat in the attic. You say it's a warm climate; is the attic air temp warm to very warm during the day? If so, you may have to consider active ventilation and/or insulation.
Yours aye, W. Underhill
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I should have mentioned earlier that I'm in Lubbock, Texas, where today the temp peaked at 99.6, with a cloudless sky. The attic is quite hot on days like this, though I haven't measured the attic temperature. And it isn't even summer yet!
thanks, Randy Norwood
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On Mon, 18 Jun 2007 18:55:32 -0700, randyn wrote:

Yes normal
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The kitchen tap is on the other side of the

Very normal. Measure the temperature in your attic and you may be surprised at how hot it is when the sun is beating on it.
We have a similar situation at work where the water lines pass through the ceiling of the boiler room. The water in the office water heater actually cools off sitting in there in the summer when the boiler room temperature is high. Now that you see how hot it is up there, consider some venting to save on AC costs.
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wrote:

Out of line with what?

Check how hot is in the attic.

Well, there is always the possibility that the plumber put in a water line heater. If he liked you a lot he might not have charged for it.
Otherwise, what kind of defect would cause the water to get hot?
Well, I am curious about black insulation. It's probably dark in the attic most of the time, but the question would be if black things also absorb infra-red, heat waves, more than white things do. But none of this matters after an hour or two, when everything reaches equilibrium afaict. That is, inslulation only slows down heat transfer, it doesn't end it. You could test this with 10 feet or more of pex that you fill from the residential part of the house and then pump somehow to the attic, surrounded by various kinds of insulation, and then wait an hour and pump it back to see how hot it is.
I'm a big believer in attic ventilation. I had full width soffits, front and back and full width ridge vents, but I still think I lowered the attic temp 20 or 30 degrees with a roof fan. That would still your water at 100 degrees for those first 10 seconds. The reason to lower the attic temp would be more to save on AC if you use that, and increase comfort of the room.

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Water is an excellent conductor of heat. Attics can easily reach 130 degrees or higher. Water sitting in a pipe in a 130-degree attic will become 130-degree water fairly quickly.

Undoubtedly. The cooler you keep the attic, the cooler the water will be.

No reason at all to suppose that it is.
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Regards,
Doug Miller (alphageek at milmac dot com)
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To the original poster. In the winter when the attic is cold you will have cold water. The better your attic is insulated and the colder it is outside the more likely the pipe in the attic will freeze solid-- then no water flow. Did the plumber consider that? How might that happen? You go away on a winter vacation, set your thermostat to about 55 degrees to save heat and Lubbock gets a long cold series of days with little sun.
On Jun 19, 7:02 am, snipped-for-privacy@milmac.com (Doug Miller) wrote:

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Yes, I was wondering about that too. Wasn't sure how cold it gets in TX in winter, but anywhere that gets substantially below freezing, this could be a problem. If the pipe can be routed under the existing insulation, next to the drywall, that would probably work for the TX climate.
I also don't agree with the advice that on a 100 deg day, with more attic ventilation the temp can be reduced from the 130 down to 100. You could get it down some, maybe 10 deg if really done well. But without some extreme air flow, you're not going to drop in to be close to ambient. Also, it's a waste of time. Because if you want a glass of cold tap water, whether it comes out 130 or 115 isn't going to make any real difference.

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