OK so I got mixed advice from IKEA as to 18 vs. 24 cabinet and my contractor (who I trust and usually agree with) installed something I can wave up at but not USE. See photo. (sigh) 18" does NOT work in my situation but he doesn't want me to get the 24" since it will hang about 1-2" below the cabinet line. But goodness below could only be better than 4" above. The problem in my kitchen is that the contractor gave us 23" of clearance from the countertop (it'll be 21" once the skirt for under cabinet lights is installed, and I'm fine with 20-21" of clearance and prefer it, but I'm 5'3" and my husband is 5'7" or 5'8" and we have a grade school child and I think 23" for reaching up to cabs is too high! I want to lower the cabs 1-2" overall but they are installed (IKEA isn't that hard to lower the rail on which they are all installed but still). Right now the microwave clearance is 26.5" from stovetop to bottom of microwave. Crazy! If we switch to a 24" cab over the microwave the clearance will still be 20.5" which I think is fine. Means our microwave will be the most accessible, vs. 23" for the cabinets. This is frustrating, if I lower the cabinets more than 1" I can't lower the microwave because it will be really too low (I wouldn't go below 19 or so clearance for microwave which we would get at 21.5 clearance for cabinets). Part of the driver for the high clearance was a 16.5" faucet (gorgeous but perhaps the wrong choice for a sink under cabinets...) and a soffit that the cabinets come to at 23" clearance. I still think we need to lower the microwave 6" and/or the cabinets 1" or 1.5". Help!!

This same question was just asked a few days ago - I'll link the thread. Not only does an OTR MW need to be open at the bottom like Hollysprings said, but an OTR MW would need (if it were even possible) a cabinet larger than 30" wide to house it. Also, the lights and fan of an OTR MW means it does not have a flat smooth surface to rest on - it must be suspended. What is it about the Whirlpool Gold OTR MW that you like? I am certain you can find all the same features in a countertop model that has a matching trim kit. Here is a link that might be useful: Thread about an OTR MW in a Cabinet

This is not something I know much about, but I'm dealing with my range hood issues at the moment. Wouldnt it be possible to mount the 16" deep microhood into an 18" deep recess so that the front is mounted as recommended, with a filler in the back between the rear of the microwave and the wall? They definitely sell "trim" accessories online, although most of these are intended to fill a gap around the front of the appliance. I can't see a reason you couldn't mount the microwave to a 2" x 4" attached to your studs, then disguise the wood from below with a stainless steel trim kit. Google "otr microhood gap fillers." Good luck!

With most OTR microwaves, I don’t think flush mounting is possible. Not because of the venting, but because of the the door swing. Typically, the hinge side of the door requires space beyond the 30” opening. On mine, the hinge projects almost 3/4" from the left side of the unit when opening, beyond the 30" width. Check that yours will open if it's recessed more deeply than usual between the cabinets. Below is a photo from above of the microwave door projection. The door thickness is just about the same depth as the top vent. If you recessed the top vent, the door wouldn't have space to open. Different models may have a better hinge setup.