I'm interested to hear what you find on this as well, since I'm also considering this combination. When I read through the specs, it seemed like it would be fine...

You may have run into the CYA factor. Normally, to get approval from such as UL, various tests have to be run. A stand-alone unit only needs to be tested by itself, but if a manufacturer wants to approve combinations, then they have to show that the combinations are safe. No manufacturer is likely to expend the effort proving competitors products will work with their unit. Hence, if a Miele oven is approved to go under a Miele cooktop, it is because they determined its safety. One expects similarity of process for Gagganau units. (In that case, sibling products such as Thermador and Bosch may be approved.) Beyond safety, there are also lifetime reliability issues that relate mainly to heat.

In fairness to the cooktop manufacturers, they have no control over how other manufacturers ovens are thermally insulated or even if the insulation on units made today is the same as on units made yesterday. There would have to be an industry-wide standardization agreement. (Waiting for you, ANSI.)

In my view, if room permitted, meeting the gap requirement for an underneath air space, below which there was added and effective insulation above the desired wall oven, might be safe for both units. (One needs to know how the induction unit actually cools itself to decide whether any particular gap is going to be sufficient. Gap access to external air may be needed, possibly forced air.) The enemy of electronics is heat, and other than the ceram top, electronics is what constitutes most of an induction cooktop.

kas

Thanks Kas, Yes, I suspect that the CYA is in play here. I know that the installation instructions for the Gaggenau combi steam states "Do not install another electrical appliance above this appliance in the cabinet." but I don't see anything similar in the convection oven instructions.

The instructions for the Miele cooktop states you "must not install a cooktop above an oven or stove unless they have a cooling fan." I need to double check, but I think the cooling fan is at the bottom of the Gagg. The Miele also talks about a protective base being allowed but not required.

I'll continue my research.

There's something else involved, or at least used to be. The manufacturers, especially in Europe where cooktop over oven is most common, design the arrangements of the parts so that they play well together. If you're only using one unit at a time, it probably doesn't matter. It's not just insulation, but locations of the fans, controls, and various bits that you want to be separated vs. those that can be close together. Sorry I can't remember the names of the bits. I think there's also an issue of how the waste heat from the induction (which there is, much as people would like to deny it) affects the oven.

Thanks Pillog. I just talked to the Gaggenau technical rep and was
advised that I can put any brand cooktop above the oven as long as the oven has its own electrical supply and otherwise meets the requirements for installation. Ditto with Miele. In fact, Miele rep made it a point to point out that their installation requirements (a) state that the clearance requirement is between the cooktop and an oven (does not specify a Miele oven), and (b) the cooktop cannot be installed over a stove or oven unless they have a built in fan.
The Miele rep said that issues with installing a cooktop over an oven are typically when the cooktop is gas.

Excellent news, Sherri! Thanks for posting the resolution.