We did this in our old house. If your microwave is built into cabinets such as pictured above (cabinets don't go to the ceil), they'll just box in the area between the cabinet top and ceiling, run a vent pipe through the cabinet above the microwave (so you lose that space) and into the attic space and put a damper roof vent to carry it away. We had this mounted on the roof and connected to the vent pipe that went through the upper cabinet, boxed space above it. and through the roof. Lowes link works, not sure why it says this
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