Is it sensible to place a bathtub under a skylight?

In the bathroom you simply lack the area under the tub, toilet, sink, so compared to other rooms of the same size you are missing 2-3sqm, possibly the shower as well (another -1sqm) and suddenly in a 12sqm bathroom you only have 8sqm of heating surface and you're supposed to reach 24 degrees with that. If there's a skylight added, that's additional heat loss... so I would calculate very precisely...

Yes, but then there's additional wall heating. It's all no problem

Those are additional costs that may arise on top of the skylight. The OP didn't know about that until just now... so all no problem, I wouldn't say that...

In the bathroom, you simply lack the area under the bathtub, toilet, sink, so compared to other rooms of the same size, you are missing 2-3sqm, possibly the shower as well (another -1sqm), and suddenly in a 12sqm bathroom you only have 8sqm of heating surface, and it still needs to reach 24 degrees. If there is also a skylight, there are further heat losses... so I would calculate very precisely...

...

But you can’t just throw that out there without even knowing how large the floor area of the bathroom will be and how tight the heating loops are laid. It depends on many factors and has hardly anything to do with a double casement window above the bathtub.

Our bathroom also partially has an artificial knee wall but is nice and warm, so we often turn the thermostat down to 1 - and yes, that works independently of the other rooms.