Well, if you are OK with shortening the life of your MW and maybe replacing it annually, then keep the one you have. Otherwise return it and get a smaller one. Study the manufacturer clearances for the different manufacturers though as each will have different clearance requirements. You might be able to find a larger capacity MW that needs less clearance than the brand you are dealing with.

Microwave ovens are typically around 65% efficient, so about a third of their rated power has to be removed by passive or active air flow. Think of a 400W lamp in the cabinet.

One possible approach other than downsizing would be to use a fan blowing the cabinet air somewhere and pulling air from the front. There are a lot of possibilities, most inconvenient or annoying to implement.

An example would be a fan mounted under the cabinet pulling air down through holes in the cabinet bottom. A thermostat would be needed to turn the fans on when significant power was being used and the cabinet interior started to warm. A quiet rack fan would be desirable if the flow rate needed could be met.

kas

i'd go with a smaller microwave like the NN-SD797S and use the 27" or 30" panasonic trim kit which allows enough clearance for ventilation.

worked great when i had to replace the old microwave at my mom's house.

FWIW, I ended up getting a smaller Panasonic microwave (not sure of the model number). It was 1.6 cubic feet vs 2.2 of the first one. It still has slightly less clearance than recommended on the sides, but 2.5x what is required above. To get one narrow enough to provide the recommended clearance would mean going down to 1.0 cubic feet or smaller. I'd rather not do that, I'll take my chances with this, and if it overheats, I'll modify the cabinetry, replace the oven, and consider it a lesson learned.

Pic below shows the original oven - clearly not enough clearance. This was not a wall oven mount, just a little enclosed space the previous owner or kitchen designer created to house a countertop microwave.

This post was edited by buddyboyinc on Tue, Jan 22, 13 at 16:13

I'm having this problem too. We are building and just bought a microwave to fit on a shelf under a cabinet, kind of like in this picture. But, reading the owners manual, it says you need 12" of venting space above! I would assume all microwaves would be similar. What do people do? Just not worry about it?

Wendys53: What mfg. and model # microwave do you have?

It is a Kenmore #72123. They do not sell a trim kit for it. How does a trim kit help the venting?

same problem with newer Toshiba models... 12 inch clearance on top...

thinking about pulling microwave from underneath cabinet onto microwave cart just enough to clear cabinet...also has a very short cord so can't just use cart..so will be leveling the microwave's back feet because cart is 1 1/2 inches taller......is this safe?