Replacing an old jenn air electric cook top with new 30" down draft gas cooktop. Need to know how to secure the cooktop to the granite countertop.

You should just be able to set the cooktop in after you attach the downdraft, usually there are tabs on the downdraft that clamp on to the granite cutout. There is probably a closed-cell foam strip that runs under the lip of the cooktop, I would just make sure it seals to the granite properly (no gaps) and put a couple dabs of silicone in between the lip of the cooktop and the granite. Usually the cooktop is heavy enough that the silicone will keep it from moving around.

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