DIY shower water heat recovery

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
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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
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Andy wrote:

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
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snipped-for-privacy@care2.com wrote:

<snip>
I was wondering about something like this. Preliminary design was:
Hair filter.
Channeled plate to take the flow of water and distribute it into an evenly falling circular curtain of 10cm diameter (or so). Copper coil, 10cm*30cm or so of close-wound pipe.
Cold comes in at bottom of coil, and leaves top warmed by the water film flowing over it.
The plus over the american 'coil wrapped round pipe' should be better heat transfer, without a long vertical drop. The minus is of course need for occasional cleaning.
To address the cleaning issue, I was planning either to make the coil completely removable, with something like (but not) hozelok connectors, or to have the channeled plate removable, so that you have access to the inside and the outside of the coil in the 20cm*30cm well it sits in.
(The well is designed to never have water sitting in it)
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Ian Stirling wrote:

I guess it would work, yes. Its adding maintenance though. But a 1' drop, if your bath's on the ground floor you probably wont have that much room.
Ah: because it would fil with muck and gunge, and people being busy with more pressing things, you'd end up with such units getting stinky. I would want to keep any possible stink gen on the other side of the water trap. But that then makes it inaccessible...
NT
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snipped-for-privacy@care2.com wrote:

A water trap could easily be done simply by making the inlet do:
| | \wwwwwwwww|wwwww|wnwww/ .\___________________/. : : : : O O : : O O
(O = pipe, : = falling water, www = water surface, n = water spirit (nymph, or similar)
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Ian Stirling wrote:

I'm a little unclear about your diagram, so I might have misinterpreted it, but its starting to look complex to construct and hard to get to the muck storage to clean it. It seems theres no free lunch.
NT
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snipped-for-privacy@care2.com wrote:

<snip> <snip>
Hokay. Bigger diagram.
Shower floor. Removable plug
_________________ ____ _____ ___________________ || |H| || |- | | -- | \_____/ | | : : | | | warm out>| O O | | : : | | O O | | : : | \ O O / <cold in \ /          \ /          \___ __/ | |              To waste.
H is a removable hair filter. Below that is a circular dish, forming a trap, over the edge of which the water flows down the heat exchanger coil. When you remove the inspection plate, which is a 20cm dia (or possibly square) door, with a seal round the edge, the trap comes with it. Then you simply take a bottle brush or something a bit fatter (there is a 5cm gap round the outside for this purpose) and clean both sides of the heat exchanger.
I'm envisioning the heat exchanger coil being fairly close wrapped, with perhaps 5mm gaps between pipes.
Inside the top of the inspection chamber are a couple of lever valves, to enable the coil to be bypassed, allowing it to be washed with very hot water.
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Ian Stirling wrote:

ahhhh, comprendi.
May I suggest a tweak: something closer to 6" high and nice and wide, so you get plenty of coil in there, and lots of surface area. And so the bath isnt half way up the wall :)
NT
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snipped-for-privacy@care2.com wrote:

<snip>
I'm not sure. At some point, as you increase in diameter for a given flow, the curtain of falling water is going to be harder and harder to get even, perhaps even leaving bits of pipe 'dry'. Then there is the issue of as you decrease the number of pipes a given bit of water flows past, you increase the temperature drop from one pipe to the next bit down, meaning that heat transfer has to be much more rapid. I _think_ that for a given flow of water, thin and long is better than short and wide. I've got to do some simple simulations though.
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Ian Stirling wrote:

true. I expect in practice it would snake about, but theres no g'tee.

erm... with wider dia, less volume of water flows per second over each degree of the pipe pancake. It also flows less distance from top to bottom. I think it balances out ok.

maybe, but I dont think this is the decider. Having the bath on the floor is more important imho than a slight thermal difference.
NT
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snipped-for-privacy@care2.com wrote:

<snip>
I'm unsure - anyway, where are the breakpoints? How much more efficient is 4 turns than 2, ...
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R.P.McMurphy brought next idea :

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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R.P.McMurphy wrote:

I havent, so take any info with this in mind. I figured a good idea might be to wrap 4 equal lengths of microbore round the copper drain pipe, soldering in place, and parallelling the microbores using a 4:1 manifold at each end. Typical lengths are 2-3' for the unit.
Reasons for paralleled microbore: 1.you get much more contact area with the drain pipe than you would with larger pipes 2. its easy to spiral it round by hand 3. Differential thermal expansion should not cause any serious problems. (untrue of long straight pipes in parallel) 4. Due to microbore flexibility, the finished structure is robust and leakproof. This is untrue of pipe-in-pipe types.
Best thing to do with this water is to feed it to the cold inlet on a thermostatic shower, as you said.
If you're creating a setup, there is another way to gain heat at very low cost, with less return than your drain exchanger. That is to use a low cost high capacity solar collector between header tank and HW tank, with draining and bypass valves for winter. By low cost I mean a pancake of plastic pipe under polythene, on either flat roof or wall.
NT
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Just a thought here - wouldn`t microbore be more prone to blockages from hair or anything else that went down the plug`ole ?
(i`ve got sod all experience of plumbing, just a wild question)
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Colin Wilson explained :

He was suggesting using the microbore for the cold feed, wrapped around a copper drain.....
Good idea BTW (using microbore).
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Harry (M1BYT) (L)
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On Wed, 01 Feb 2006 18:49:32 +0000, Harry Bloomfield wrote:

This has come up from time to time as a suggestion.
I am fairly sure that copper waste pipe is compatible with the push fit waste fittings.
A problem I can aticipate if this works is that you will have to keep upping the flow rate from the electric shower using the temperature adjuster. You may run out of travel and need to have a shower which you can then put on half power.
You may well have already thought this through but the outlet from the microbore pre-heater should be at the plug hole of the bath/shower-tray.
I'd try 'tack' soldering the microbore to the water pipe using potable 'green' lead-free solder every 25cm or so and then come along after using CH/gas pipe leaded solder (which has a lower melting point) to finish the job.
It might just be possible to turn a typical 9kW Electric shower into a 20kW shower typical from a combi.
Just to save a +lot+ of hassle I'd put some 1/4 turn bypass isolators around the gizmo - you'd be pretty pissed off if you found you could not get the water through fast enough in August to shower safely.
Note that only the better stocked PMs will have 35/42/50 mm Cu pipe.
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Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
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Thanks for all the ideas, I think im going down the 'meter-of-copper-pipe-with-microbore-soldered/braised-to-it' route. where can I get the copper pipe from of the right size that will fit straight into the ubend from the shower? what size? also concerned about making sure flow rate is not restricted....how many 10mm or 8mm microbore will I need to wrap around the copper waste pipe to keep a free flowing run from the 22 mm supply?
Oh by the way im not using an electric shower, im using a thermostatic shower valve, http://tinyurl.com/dwmdb supplied from a 3bar pump http://tinyurl.com/bl5ou .
Steve
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On Wed, 01 Feb 2006 20:56:24 +0000, R.P.McMurphy wrote:

As I said in my reply ">> Note that only the better stocked PMs will have 35/42/50 mm Cu pipe." The 42mm pipe will fit in the outlet of the shower trap. And I think it will fit into pushfit waste fittings aswell as compression type (of course).
Since there are 4x10 to 1x22 'manifolds' available I think you should go with that on pragmatic grounds.
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
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snipped-for-privacy@care2.com wrote:

And then wrap the whole thing in thick insulation.
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