On Mon, 18 Jun 2007 18:55:32 -0700, randyn
wrote:

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.

Out of line with what?

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.

Check how hot is in the attic.

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?

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.

Thanks