Waste water heat recovery

Hi all,
has anyone had any experience with waste water heat recovery systems?
Seems like a great idea, but might not be suitable for retrofit, rather just at point of build.

If anyone has, like to hear your experiences and see if it is indeed worth it as a retrofit

I do not have such a system although I would like two. I think that you need to incorporate the system into a bathroom refurbishment rather than a retrofit. Then you have the plumbing exposed anyway.

I thought of a concept a bit similar to this a few years ago (it would certainly take some of the guilt out of taking indulgent showers!)…