[villagetinker]

Originally Posted by EdFNJ

. In MY case, the microwave does have a OPTIONAL knockout vent but was NOT vented when the house was built (~2009) and there are not cutouts anywhere or could there be due to the configuration. (The microwave there now has been replaced since the original and the original also had a sealed knockout for an optional duct. Would obviously have to remove the microwave for a range hood and go "countertop" for it.

Ed, I would get a stud finder to see where the studs are, if you are lucky, they will be to the right and left of center where the microwave is located. If that is the case you may be able to have the vent installed inside the wall. If this is load bearing, then you may have to go through the cabinet, and outside the wall and then through the ceiling. Depending on what is on the other side of the wall you may be able to go through the wall to the other side and then up through the ceiling and to the roof.
IMHO, you will have the same concerns if you remove the microwave that put in a hood, so getting the vent in for the microwave is probably the best option and least cost option.