I just bought an outside vent microwave about 6 months ago and no sales person ever asked about vent location so either I was really lucky they matched exactly or the location is standard. you could look at the online manuals for several models and compare the specs also or go to an appliance storemand inquire

Frankly, I think it all depends on your cooking style. I have an OTR micro and in my kitchen reno last summer I put the old one right back over the range. It's almost 10 years old, and still looks brand new and I do a LOT of cooking; however, I never do deep fat frying. Before the reno, it was not vented to the outside - it is now. It works fine for the type of cooking I do - both long term and short term stove top and oven-type cooking and baking. I have never - and I repeat NEVER - had more than a few spatters of grease which I clean up immediately after cooking as part of the clean-up process. If i would have put in a "real' hood (which by the way would have cost just about the same as the cabinets and trim for the OTR) the micro would have ended up in a very awkward location - not all of us have the luxury of a large kitchen area. Although my kitchen is considered large by my friends, in actuality the working kitchen is only 13x10, with several doorways. Just like in decorating, while vertical blinds might be 'dated', sometimes they're the best solution to a window/door problem. So...sometimes the best solution is an OTR - you go with what works for you. Helene

Harrietthehomeowner, I replaced my BRAND NEW OTR MW with a hood about 3 months after I installed the OTR MW in my brand new kitchen. I really detested that MW. I think you said you already have the ductwork, right? Then I don't know why you believe you'll need electrical work (the MW needs electricity, so if you already have the electricity for the MW you don't need more electrical work), carpentry (why?) and drywall repair (why?). The biggest expense in my replacement was the hood itself. Countertop MW's these days are pretty low-cost. I bought a large countertop MW, with actually bigger interior space than my OTR MW, with all the bells and whistles like sensor cook, several defrost modes, etc., except convection (I didn't want convection). That Sharp countertop MW cost me about $120. I put my MW on a shelf in my pantry. The other expense was tiling. I had a backsplash up to where the OTR MW was. But the hood is higher, and so I needed to bring my tile guy back to fill in that space, I think it was 3-4 rows, 30" width, so wasn't that big of a deal. Luckily, I had plenty of extra tile from when he did the backsplash in the first place. I sold my OTR MW on Craig's List, which wasn't too hard since it was practically new, although I could have also donated it to Habitat for Humanity, but it didn't occur to me at the time. Here's why I detested my OTR MW: - OTR MW's just have a couple of little mesh screens for exhaust, very inadequate. - capture area is a joke. Since the MW only hangs over the back burners, it can't capture anything coming from the front burners, and even the back burners are inadequately captured, given the little mesh screens I already mentioned. - my OTR specified 300 cfms, but hardly exhausted anything. - little mesh screens got clogged very quickly, since they are so small, making the exhaust even less effective than it already was. - as a short person, I found it awkward trying to peer up into the MW to check on things cooking. - OTR MW is really noisy. My replacement hood isn't dead silent either, and in fact I believe no hood is unless it has a remote or in-line fan. But that OTR MW exhaust fan was like having a 747 in my kitchen. I do understand that in a small kitchen, sometimes the only spot for a MW is OTR. But barring that, I wouldn't recommend one.

Manufacturer's preference primarily. Microwaves (even ones combined with a kitchen fan) are "expendable" consumer items and tend to be cord-and-plug connected. Hoods and regular stoves/ranges tend to be "fixtures" and hardwired, but that's not a rule.