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Robert Gammon wrote:
wrote:
A 200' version makes 82%...

But that's pretty big. How about this?

We collect all the shower water in a tank, with an infinite cold
water tank next to it, then circulate the cold water through a coil
in the shower tank until it all cools to the cold water temp... Then
again, infinite tanks are hard to come by.

So maybe mix hot and cold fresh water to 90 F and circulate that
through the coil until the shower tank drops from 100 to 95, then
pump some of the 95 F fresh water back into the hot water tank and add
enough
cold fresh water to make the fresh mix 85, then circulate for a
while, then pump some 90 F fresh water back into the hot water tank
and add enough cold water to make the fresh mix 80, and so on. How
can we do this automatically, on a continuous basis? We need a 20 gallon
expansion tank too. Lots of
pumping, but little energy, if the hot and cold supplies stay
pressurized.

At some point the water needs to be heated to about 140F to kill bacteria
before use in showers and baths.

No it doesnt.

I fail to see the point of all this pumping and mixing between hot and
cold sources. What do we gain by this??

Bronze Taco pumps are cheap and use less than 100W to move 10+Gal/Hr
to 15 feet or more.