Today, (April 10, 2010) I got a reply about this Ebay item..


I apologize for the late response but our home burned down. The unit is designed for shower / tub drains, it is 18" long 1.5" drain in and out and 3/4 lines for inlets and outlets. The units is assembles from copper and is soldered. Unit is sealed in PVC and filled with foam to retain the heat. I have tested the units to 80 psi for city water pressure but not higher, I do believe they would hold 100 psi. The flow rate at 60 psi is 4.5 gpm.

- davee4089

Making a Copper Coil...
 

Here is a scan from a book that is no longer in print:


...the picture tells the story.

The coil shown in the photo is meant to go into a chimney pipe for heat recovery, so the precise internal and external dimensions are not so critical. If the coil was intended to wrap around a waste pipe for heat recovery, the internal diameter of the coil would be critical. When wrapping such a coil, a certain amount of "spring-back" will occur, so some experimentation would be required to make a mandrel (a log in the picture) of such a diameter so that contact between the formed coil and the copper waste water pipe would happen. Then, soldering would really improve the situation.


Regards,

-AC_Hacker

I have a good commercial unit, and on inspection can see the copper water pipe was soldered to the copper drain pipe before starting the coil. It was wound so tight, the 1/2" copper looks pressed - with squared edges for extremely tight contact.

Another embodiment
sdinfo.ru/waste-water-heat-recovery

necro-ing, because 1/2 copper tubing was on clearance at my local Lowe's for $1.79. Just need to find some cheap copper DWV now.

Don't have enough posts for the link, search for "1/2-in dia x 20-ft L Copper L Coil" to check yours. Was only that price at one store, so ymmv.

Here was my take on it.
http://ecorenovator.org/forum/conser...exchanger.html