Heat recovery from shower water - is it sensible?

You can also turn back time. Showering once a week is enough.

I don't know what you research all day, but your questions so far are more like the third decimal place when it comes to building. A good design (compact, little envelope surface, optimized thermal bridges, windows of the right size in the right place, reasonable and adjustable shading, well-planned heat pump with photovoltaics) will benefit you much more than shower drain heat recovery, room-by-room demand-controlled ventilation, or obscure all-in-one compact devices.

You are probably right, Hangman. After all, I am open to new optimization ideas that are not run-of-the-mill :) . My next topic would then be the wall-mounted hybrid heat pump - and just to annoy you ;-)

I came across shower water heat recovery systems (e.g., in the drain channel) during research. Does anyone here use them?
It could be that the acquisition and installation costs question the economic viability...

From an energy-saving perspective, this makes absolute sense. Therefore, these systems are not only justified but also have a good future. Whether the systems already bring economic advantages now, I cannot say; I am skeptical.

A lot of heat also goes into the air and is hopefully immediately reused via the ventilation system. I also wonder how the cleaning of such a system (hair, soap scum, grime, etc.) will be. If dirt accumulates around any thin slats/tubes, the effectiveness will also decrease significantly...

I waited for the points to finally come… In the rental property it is of course different, there the water goes directly into the stack and is gone. In an owner-occupied property, it sometimes runs several meters through the heated envelope and can transfer the energy to it in the meantime, even without an extra heat recovery system in the wastewater stack. When it comes to cleaning, it depends on what exactly was installed.