Hot water circulation pipe - How should the insulation look like?

I have seen pre-insulated composite pipe with 20x2 and 13mm insulation... that would also be sufficient.
At least in the shafts. These run through heated rooms. Then possibly only exchange it in the basement if the insulation is too thin for another one.

No one here can answer that because no one knows the pipe routes in your house. So your plumber is actually the right contact!

I wouldn't be surprised if you need a 25 mm pipe + insulation in the basement – it has to be insulated multilayer composite pipe – and can only step down to 20 or smaller on the floors; it also depends on the consumers and their type. Furthermore, the choice of material also depends on your craftsman's press; not every press/press jaw corresponds to every multilayer composite pipe.

By the way, I just realized where are you hiding....

Rhenish greetings

Why does a craftsman always have to do everything, somehow I no longer understand the point of hardware stores or specialist retailers that sell to private individuals.

Painting, laying flooring, drywall work, retrofitting a roof with insulation between the rafters if you have some idea what you’re doing, tiling and especially a lot in the area of outdoor facilities -> There are plenty of uncomplicated trades where you can indulge yourself as a hobby.

When it comes to water, gas, and electricity, a layperson should probably really keep their hands off. The legal basis arises, as far as I know, from the technical connection conditions of the supplier.

On Bosy it is quite well stated what is sufficient and what is not. 100% energy saving regulation is, however, more like 40mm+ for most materials.

Painting, laying floor coverings, drywall work, retrofitting the roof with insulation between the rafters if you have a rough idea of what you're doing, tiling and above all lots of work in the area of exterior landscaping -> There are plenty of uncritical trades where you can tinker around as a hobby.

When it comes to water, gas and electricity, as a layperson you should probably really keep your hands off. The legal basis is, in my understanding, derived from the technical connection conditions of the utility provider.

With gas, there are probably no two opinions that you should know what you're doing. Otherwise, for example, electrical work must be approved by a professional anyway. So if you know which cables go where, anyone can lay them. Likewise, connecting a socket can be done by an elementary school student. I find tiling much more demanding, for example. But as a layperson, you can take your time with it, and it usually turns out just as well as with the professional tiler. Some people must really have two left hands and, on top of that, ten thumbs, judging by some of the things I read here.

...or simply a different focus in life.

...or simply a different focus in life.

But then that is HER focus.
If someone says they would like to do this or that, there is no need to spread panic about what does NOT work.
For example, driving a car is by far much more complex than laying a cable and connecting a socket.