Control of underfloor heating using thermal imaging camera, insulation?

....My concern was only regarding a freestanding island, as it must be firmly anchored to the floor. ....

That’s not entirely correct now. The island supports itself easily due to its own weight. At 60 cm depth, you can consider it. But even here, underfloor heating is not a problem since the feet are then glued. For this, I use raised floor supports and keep the plastic feet for attaching the baseboards. To make the underfloor heating visible, I use thermal foil if it is absolutely necessary to screw something into the floor. So far, everything has worked out well.
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Regards, Sigi

That's not quite right now. The island supports itself easily through its own weight. With a depth of 60 cm you might consider it. But even here underfloor heating is not a problem, because the feet are then glued. For that, I use double floor supports and keep the plastic feet for attaching the base panels.

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Regards, Sigi

That's EXACTLY how they did it - I believe - with us. However, in the kitchen plan it was specified with the cutout - maybe that's because we only have drawers! over 180 cm length?

The underfloor heating can be thermographically inspected at any time of the year. The thermography is done during the warm-up phase. That means: turn off the underfloor heating one day in advance. The next day, turn it on and carry out the thermography. After about 20 minutes, the first heating coils become visible.

The excerpts have nothing to do with it, unless you all loaded with 50kg and all opened at the same time and the island is only 60cm deep. They probably wanted to install it earthquake-proof.

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Regards Sigi

To return to the original question, I have myself taken a few images with a thermal imaging camera. Normally, you will not be able to see the individual heating coils or how close they are laid because the screed and the floor covering heat up and distribute the heat accordingly. However, if, for example, no pipe is laid under a kitchen unit or similar, you will clearly see or even feel that with the camera, as well as barefoot in winter.

I also have heating coils under the kitchen island because it might be that with a new kitchen it will have a different size at some point. But since it was quite difficult for 5 people to carry the countertop alone, I really don't worry about moving it.