Our over-the-range microwave is currently configured for recirculating ventilation, which is less than ideal for many reasons (one of which being that it's over a gas range..). We discovered that there is ductwork behind the microwave that vents outside but the microwave was never connected, and the ductwork was not installed high enough for a typical rear-vented microwave exhaust (for reference, the house was built 2008). After pulling the microwave down, we found the first picture: looks like someone found there is ductwork and didn't explore any further? I decided to cut out more drywall to see what is going on. Turns out there is what appears to be a roughly 30x3.25" rectangular duct that extends down the wall about 2ft, then connects to an oval duct on the left side that makes its way out of the house. This interior wall is framed with 2x6 and OSB on the opposite side, most likely because it's a large vaulted ceiling behind here. They notched out the 2x6 to accommodate the rectangular ductwork. So, I'm looking for advice on the best way to vent my microwave here. I'd prefer to avoid cutting into the upper cabinet, so I'm leaning towards continuing the notch of the 2x6 all the way up to the cabinet (the 2x6 is not centered and would block one of the rear exhaust vents of the microwave), cutting out a 10x3.25" hole in the existing ductwork, and finding some way to attach and seal something like this. Does that make sense? Any alternative suggestions?
