Andy wrote:
"R.P.McMurphy" wrote in message
...
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.

Has anyone had a go at building one?

Steve

I'm thinking of the same thing myself, but don't know of any product. On
problem is that the waste water contain scum and hair, bits of soap etc, and
it's low pressure so cannibalising a boiler heat exchanger won't work. I'm
thinking of coiled microbore piping ( several in parallel ) inside a flat
box where the waste water can hang about for a few seconds. The other option
is to redirect the trap outlet so that it goes to a length of 40mm waste
pipe inside which some copper tube could be coiled for the cold water, the
40mm waste eventually conecting back up with the old waste outlet.

many configurations possible, all with small problems involved

Andy


I would avoid any version with cold pipes inside the drain pipe myself.
You'd soon have these problems:

1. soap, hair, grease build up round the cold pipe, making for much
reduced heat transfer.
2. This muck-catching arrangement causes a pipe block
3. It also causes a foul smell outside, if you have an open drain,
since much muck is perpetually trapped in there.
4. You cant clear it by rodding.
5. And if Murphys law holds true, your drain rod will jam solid inside
the piping.

If you must use a pipe-in-pipe, have the drain as the central pipe.

I would be hesitant to make them this way as diffrential thermal
expansion could cause a lot of stress, and solder is a very soft metal.
Wrapping microbore round the drain pipe eliminates these problems,
though it does mean a fair amount of soldering. Its possible it may
work ok unsoldered, eg with some grease and zinc oxide wiped where the
pipes touch, and just some solder at each end, or maybe even large a
stainless jubilee clip.

BTW theres no point insulating the thing once made. If you've got
insulation to use, put it somewhere on the hot pipe.


NT