The figures are there. The £ is higher than the $ at the mo, so it is a
matter of the shipping cost to add on.
You can make your own using two large bore copper pipes. One inside the
other. The mains water is in the gap between the two. Using two reducing
elbows and filing out the pipe stops inside the the fittings so the inner
pipe can slip you can easily make one yourself. Once filed out you solder
it up with a powerful blowtorch and wrap with insulation.
Start again.. Lets have 15mm and 22mm pipe for understanding.
- 1 three metre lengty of 22mm pipe
- 1 three metre lengty of 15 mm pipe
- 2 solder ring capilary 22mm x 22mm x 15mm tess. (that is a 22mm in the
centre of the tee)
- File out the the 15mm stops of each tee to make then slip 15mm pipe. Easy
enough, just elbow grease. Or drill it out if you have the right sized
- Cut the 22mm pipe to 2.5 metres in length
- Insert the tee on the 22mm pipe at one on each end.
- Run the 15mm pipe though one tee anmd push it until it reaches the other
end and run it through the slip of the other tee.
- Have the tees 180 dregrees to each other
- Solder up.
- Cover with insulation.
You then have cold water running through the 22mm tee and out the other tee
warmed up. The hot waste runs down the 15mm. This is now an effective heat
exhanger. The longer the better. I have done these over 20 foot in length
ona solar water heater and it was very effective and very cheap.
You size up the copper pipe to suit eithe a shower or a full 110mm waste.
Sounds okay but surely for a long run the inner pipe - which appears to be
unsupported except at the ends - will touch the outer in various random
places and cause turbulence and resistance to flow. I don't know if this
will be a problem or not so could you let me know what sort of peak flow did
you get through the 20 foot long one ?
AIUI, that's using Screwfix catalogue as an example
part code D90193 ?
that's be (?)
Hot(!) Cold out ^ Cold(!) Cold in
22 ------/ /----------------------- 22
Waste -Hot >15 ----->--->----/ /--->------------>---------15 Waste
Out of interest; - how do you get from a 40mm plastic waste pipe
onto a 15mm copper 'waste'? Isn't the 15mm waste outlet a
trifle slow? BTW, a 'new' bathroom is on the list once I've
got the correct tuits - I've indicated to my wife that I've only got
square tuits left from the last big-job - So I'm genuinely interested
in heat-recovery devices as I'm always annoyed when joules of
decent heat-energy goes down the plug-hole after each bath.
I'd also be interested in where-abouts the tepid (cold) water
could be introduced into the domestic-hot-water system.
I can't understand the drawing, but I think you have it.
I gave 15mm and 22mm for an easy to understand example. I did say size the
pipes up to suit the shower application. It makes a heat exchanger like
this once in 15mm and 22mm pipe. These days plate heat exchangers can do
the job as well or better. But using 15mm and 2mm is cheap, very cheap, as
long as you have the space to run it. You can spiral it around a loft or
basement, or under a floor.
See the web site I gave for gfx. They give e.g's. of how and where to
connect. Using large bore copper pipe this should be easy enough to make and
far cheaper than what gfx charge. It has to be fixed in a vertical
position. When water goes down the drain it spirals around the outside of a
pipe making this form of heat recovery possible.
I suppose technically it doesnt if youre wiling to risk replumbing it.
Preferable to make it maintainable I think.
Have you actually done this, at 20ft long? The reason I didnt suggest
this approach is differential thermal expansion. I cant imagine how a
soldered joint would survive in such a creation. Sounds like a real
recipe for leakage to me. One could certainly do it with flexible
copper tube, but I dont know where youd get that in such a large size.
why do you recommend 3m? And more to the point, why 20ft? Theyre
why do you recommend solder, which is soft and cracks easily, when the
2 tubes have differential thermal expension?
why do you recommend insulation? I'm not clear why cold to lukewarm
flow, which is what goes round the outside, would need insulation. Most
of the time it just sits there cold. I would think insulation might
trap condensate and cause mould.
I think if youve got insulation to play with there would be much more
effective places to put it.
Where do you get the 110mm copper fittings? And how do you drill 110mm
holes in them?
You've got 2 options for the warmed water, and 2 options for the drain
warmed water can go either:
to the cold input of the shower
or to the cold fill on the house's hot tank.
And the waste side can handle either:
the output from the shower
or the total grey water drain output of the whole house.
The logical thing is to have it either handling shower in and shower
out, or house in and house out.
Fitting vertically gives ideal performance, but they also work well
Note the 2 flows should go in opposite directions to get effective heat
Of course. The payback is around 100% pa if youve got 4 people in the
house. Thats why we're talking about putting them in during a refit.
FFS how many showers do you people have a day.
Has anyone given the slightest thought to how efficient this will be, and
the likely rise in temperature achievable.
Even I cant be bothered to build one of these.
There are only two ways this will save energy.
1) You can set the shower to half heat (assuming it has such a setting).
2) The greater flow of water permits you to have a shorter shower.
I'd guess that it would take a few minutes before there was much benefit
from the heat recovery (the shower tray has to be warmed up and the trap
water and the waste pipe itself.)
The benefits would likely be taken mostly in improved luxury rather than
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Ed Sirett email@example.com typed:
And somewhere to fit the thing, did you note the size!
"GFX can cut one of the largest peak water heater loads, the shower, by
Rollocks, did Dimm invent this
You would save more energy per year by shooting the cat and boarding up the
Or trying to recover more of the lost heat going up the chimney/flue.
Another know-it-all. Do a Google on groups and type in gfx. If you did
that first you wouldn't nake such an idiot of yourself. There are some
Americans who have these installed and reported figures on them. The average
temp rise is 17C. In effect it makes your cylinder bigger too. When
showering they are effective because you are heating the incoming cold water
with waste water simultaneously.
Domestic applications have a far loger payback than commercial. Heavy use
of waste water would make it feasible, in places sucj as hotels. Make your
own, as in solar panels, and the payback is quite quick. See my post on
ive built two of these, BP1 was 25m ( note 25 meters !) of 8mm pipe coiled
inside a 150mm soil pipe with stop-ends fitted with 1-1/2 waste fittings to
connect to shower 3ft away, cold water flow was set to 1gpm.
After running hot shower for 15 min to ensure everything had warmed up I
measured the input and output temperatures, the gain was a staggering
............... 1 deg C
Having realised I need a MUCH bigger heat exchanger came BP2.
This one would be completely impractical to actually use but..
A friend was ripping out a warm-air CH boiler, Ah that looks big enough.
So I built a tank to hold HE and arranged plumbing so the tank filled with
warm water before exiting, same flow rate and test as before.
The gain in temp was 4 deg C
Conclusion, don't bother unless you are chucking huge amounts of hot water
down the drain, fit solar panels instead.
(Dimm design quote: 1 three metre lengty of 22mm pipe, still making me LOL )
You are obviously and idiot and did it wrong...and can't read either. The
US governments tested it and says: "The key to this patented device was the
inventor's observation that wastewater clings in a film-like fashion to the
inside wall of the pipe as it undergoes gravity flow in the open drain, and
this warm, falling film transfers heat through the pipe"
The pipe has top be "smooth" in the inside. Boy are you dumb!
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