R.P.McMurphy brought next idea :
I am turning a small box room into a wet room with a high flow shower.
However id like to keep running cost right down so am considering trying to
recover the heat in the waste water going down the plug hole to preheat the
cold water going into the thermostatic shower valve.

I cant seem to find any products for sale in the uk that do this, so am
considering making one myself.

I would run an outlet copper pipe close to the cold inlet for as long a
distance as possible, perhaps ensuring good thermal contact by
soldering the two side by side and wrapping insulation round the pair.
The larger the two pipes and slower the flow through them, the more
heat will be transfered between them.



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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk