now you got me thinking
Of a simple heat exchanger from the warm drain water to the cold intake water.
Could wrap the cold water(copper) pipe around a (copper) shower drain pipe then into your shower floor to maximize the heat transfer to the cold water pipe.
I am no expert with the heat conductivity of pex compared to copper so I included a link to a pdf file from an expert
http://ascpro0.ascweb.org/archives/c...T192002010.pdf
Thermal Conductivity
Cooper ~ 401W/mk
Pex ~ 0.41W/mk yes 0.41 !
The SI unit W/mK indicates the amount of energy in Watts or one
joule per second taking into consideration the thickness of
the material in meters and the temperature in Kelvin’s
Just using copper with your idea would be good too