Whatever sound absorbing material you use must not be flammable. I placed some aluminum foil backed wall insulation within the top of an OTR microwave which would normally hold the charcoal filter if the microwave had been installed to re-circulate air. The material I used did cut down on the air movement noise considerably. Denser material glued to the sides of the metal work would have absorbed conducted vibrations such as the buzzing motor you mention.

A real hood, mounted under-cabinet, will surely be better than an OTR microwave oven attempting to perform kitchen ventilation. A real hood rated at 400 CFM, and not too restricted by the house's ability to provide MUA, given short duct to outside without too many bends, might flow 250 - 300 CFM. I am confidant that any microwave oven claimed to be 400 CFM is actually just a 400 CFM in open air fan buried in the MW's tortuous duct path. I'd be surprised if it could flow even 200 CFM net. Note that the 400 CFM MUA rule is for hoods ducted outside; if a filtered (surely) recirculating hood were used, there is no MUA issue. VaH make an expensive but reportedly adequate for real cooking ARS recirculating hood. It might not fit your circumstances. ralph_zone8_ncwrote: "I agree the microvisor is just an eyebrow but wouldn't it block the air from going up to the ceiling and surrounding cabinets and if I turn the vent of the microwave to pull air, wouldnt it be able to capture some of the air?" With respect to eyebrow capture, it will (temporarily*) capture any part of the cooking plumes that strike it. However, they will reflect out again into the room if the blower flow rate is not high enough. Flow rate needed to assure successful capture and containment depends on the temperature of the grease being vaporized and the area over which the grease plume is being generated and whether combustion products are entrained. I recommend for most a value of 90 ft/min under the entire hood aperture when cooking with gas. This corresponds to 90 CFM per square foot of aperture. The value 60 may suffice if an induction cooktop is being used. But please note from the Figure 4 table on page 9 of Greenheck's guide -- your needed (or at least recommended) flow rate (CFM) may vary. http://www.greenheck.com/media/pdf/otherinfo/KVSApplDesign_catalog.pdf ----- *Because this eyebrow has minimal depth, the blower flow rate in its vicinity will be less than the average over the capture area. Reflection, at least of hot grease vapor may be insurmountable with a microwave oven fan system. Water vapor might be adequately dealt with if it makes it that high.

I'm excited by this, too! I love the placement of my microwave above the stove and was feeling sad that my eventual kitchen facelift might eliminate it. Like Sherriode I have exterior wall placement so I'll add ductwork to the project and hopefully keep steam away from my upper cabinet doors. I see lots of pasta and lobster in my future!

So to answer questions back from you all... Re photos - in the top photo you see the empty space where the microwave should be installed, and the upper cabinets above it that were supposed to house the vent/duct into the wall to run outside. The contractor ran the venting to come in from the ceiling instead of into the back of the upper cabinets above the microwave. The second photo was one attempt at a solution- to stack a 2nd cabinet on top of the uppers. Not a great fix in my opinion. The microwave is existing and was less than 1 y/o so no need to replace it. This is a remodel not a new build and all the electrical etc was set up there for a stove/microwave combo I guess short of buying another upper cabinet w/ different dimensions, or custom building some sort of surround for the vent, I don't really have any other ideas. But at least you guys validated what I had already researched as options. Thanks.