Venting OTR microwave
Not my area of expertise, but I would opt for gutting the old inline. Seems to me if you don't turn on the inline while using the microwave, you're not getting the full benefit of the vent. And if/when, one day down the line, the inline fan craps out, it's kind of an obstruction in your vent.........just my opinion. (And I'd just take out the fan if the sheetmetal itself is sound.)
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