I completely agree with JYL that a vertical orientation does a far better job than a horizontal application. In the situation I had, there was only room for a horizontal installation - and this was some 20+ years ago.

Secondly, I used sand inside the copper outside spiral tube to prevent it from completely kinking shut while wrapping it around the larger copper pipe. I soldered a cap on one end of the tubing, poured dry sand in, tapped it to get rid of voids, filled it completely and soldered another cap on. Despite care, there was still some flattening, but this actually helps to allow better heat transfer (as has been pointed out).

Thirdly, I would have the slightly warmed water go to a preholding tank. The BTUs are stored there with almost no loss (no large delta T).

Lastly, the costs of a commercially produced gray water recovery/installation are many hundreds of $. The cost to do this yourself is a minute fraction of that. When home brewed, you get a large ROI, which I doubt would be the case with a commercial unit and commercial installation.

The colder your incoming water, the faster your ROI. My water temp is about 58F, but I know from friends in Vermont (40 F water), that similar installations on the dishwasher, shower/tub drain have saved a lot.

Find a friendly recycling place - a 6 pack of brew in the foreman's car helps a lot.

Steve

DIY waste water heat recovery

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

translate the language, you can use google translate

Drake, sorry I haven't been on this part of the forum for a while and didn't see your question until just now. The water from the bath goes through a sand filter and then into a 250 gallon tank. The toilets are plumbed directly to this tank, which has a solar powered pressure boost pump on it. When the toilet is flushed, the pipework pressure drops, which turns on the tank pump. It runs until the toilet fills, the valve shuts, pipeline pressure rises above a preset point and then turns the pump off. This saves a massive 43% on our water usage. Cost to install was $50 for the 1000 litre IBC tank, $70 for the pump and then a bit of cable and pipe. Water here is $9 per 1000 litres. Typically our 4 person house does 35 flushes a day at 6 litres each, so this saves $1.89 per day, or $690 a year. Our actual water bill is $918.14. It was $1608.48.