On Mar 15, 3:14*pm, 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.

OP-
Speedy Jim is on the right track about 3/4" vs 1/2" (both nominal
size copper tube) but unless my calcs are wrong...the 3/4" tube will
have closer to twice as much cold water volume to clear. This will
double your hot water wait time.

Why does the copper need replacing? acidic water? leaks?

I dont see why varying pipe size would otherwise cause problems.

cheers
Bob