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?
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
"Take sides! Always take sides! You may sometimes be wrong - but the man
who refuses to take sides must *always* be wrong! Heaven save us from
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!
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.
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
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.
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, firstname.lastname@example.org (Doug Miller) wrote:
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
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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