I had a great idea for recovering all the btu's which normally just go down the drain. I did a little search on google, and found out that a company STOLE my idea--almost twenty years before I had it! Check it out:

http://oikos.com/gfx/index.html

Here's some similar ideas:

Bury supply pipes deep enough to have warmer water into house (save many kwh per year)

Wrap a “coil”, which can be square, actually, using oversize pipe to minimize friction loss, on top of septic tank, cover with rigid insulation, make sure that septic tank area has foolproof drainage to avoid cross contamination. Preheats water supply, saving big $$

Put manifold, pipes, in or under slab construction, and run cold water through it. Cools slab, warms irrigation water. Also, run main supply pipe through slab to preheat water to water heater, etc.

Run drain pipe from house alongside supply pipe (again, provide drainage protection to prevent cross contamination)

Run drainpipe alongside underground pipes of ground source heat pump.

These are very preliminary ideas; some of them will require some valving in oreder to utilize them only in the appropriate seasons..

Obviously, most of them are more practical for new construction.

Gotta go,

JOJ

-- jumpoff joe (jumpoff@ecoweb.net), August 07, 2001