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Bob F

wrote:
On Mon, 16 Mar 2009 15:07:29 -0700 (PDT), fftt
wrote:

On Mar 16, 11:28 am, wrote:
On Sun, 15 Mar 2009 17:14:08 -0500, Speedy Jim

wrote:
Bert Byfield wrote:
I've got a basement full of old half-inch copper pipe, and some
of it needs to be replaced. I want to do repairs in 3/4" pipe but
I'm wondering if that will cause problems with the water changing
pipe sizes on its way to an outlet. Can I do this?

It will cause a problem if there are long runs on the Hot side.
3/4" pipe has roughly 50% more area than 1/2", meaning that
50% more volume of water has to be drawn from a distant faucet
before Hot water arrives. That may be trivial or it may be a
real pain in the neck.

That's why they sell foam pipe insulation !!!!!!

Foam pipe insulation will only cut the hot water wait time by an
insignificant fraction of the current wait time.

Wait time is driven by hot water flow rate to the fixture and volume
of cold water sitting in the hot water piping to the fixture.
Volume of cold water in the hot water piping to the fixture is
determined by run length & pipe size.

Typical hot water pipe insulation will reduce heat loss while the
water is being delivered but it wont keep it hot forever (overnight)

cheers
Bob

Guess it depends on the length of the pipes. I have never lived in a
house with hot water pipes that are much longer than 25 feet or so.
Most builders place the water heater in a central location. Of course
these rediculously large homes they build these days are probably
another story.

The only way insulation could solve the problem is if the pipes are VERY short,
and the water heater has no heat trap at all.