Sorry so long on the replies, but got a bug or something and have been laid up for DAYS. Hey Stooxie, this is how the exhausting up v down situation has been explained to me: I cannot go up because the joists are running in the wrong direction. There is no wall running so that I could duct with the joists--there is a stairwell involved as well. Is there an UP way around this, or are 3 people (from various companies) ALL wrong? I know with enough money ANYTHING can be done, however, all 3 people said that it would take something close to an act of God to make the up exhaust happen. NOW I find out that you can't duct the OTR micro down anyway--it looses whatever suck it does have, so I am back to square one. My only options: separate out the various range parts (exhaust, oven, cooktop) in order to get a telescoping downdraft exhaust that's only slightly better than a micro hood and costs a fortune and I can put the blower in the crawlspace OR If I get a hood (thank you Davidro1 for the link...very helpful) and downdraft it then I have absolutely no place for the microwave unless I put it on a micro cart--you know the carts of yore olden times! I am totally at a loss here. I honestly would not mind considering spending the $$ on the telescoping downdraft option if it worked. But according to what I've read here, they just don't. So what to do? I currently have a free-standing range now. If I split out the range into pieces parts, I end up with having to build 2 cabinets (I have a teeny kitchen with, get this, custom made cabinets -- prior owners/builders must have been sniffing glue) one for the cooktop and another one to hold the wall oven. I can't build out a wall to hold the wall oven because, again, all the walls are taken or are doorways, walkways or bay windows. Wow....what a dilemma.

Get a HVAC professional involved before saying something "can't" be done. I've had plenty of ducts run through the top shelf of cabinets or on top of cabinets behind a tall crown. There are gazillions of ways to accomplish what needs to be accomplished, and expert creative eyes can probably give you better direction in person. Ducting down can be done as a very last resort, as it's the worst possible choice, but it will greatly increase your CFM needs as it will involve so many turns. And it will be a lot noisier because of the increased CFM needed to deal with those turns. You will need insulated duct, to avoid the steam condensing in the duct. Even so, you will still need a bleed access point for maintanence because of the downward and horizontal length of the duct. The steam will naturally cool over the distance and condense into water and run to the lowest point in the system.

This will sound strange, but I don't have any exterior walls in my kitchen. An addition was put onto the house that eliminated the exterior wall, so my kitchen area, which is more or less in the center of the house, has an island and a peninsula, with rooms adjacent to both sides. There is a wall of closets at the far end which are used for pantry storage. The garage is on the other side of that wall. If those closets were removed, the wall could accommodate my double wall ovens and cooktop, and the cooktop could be vented to the garage, and maybe even to the outside. Let me ask a naive question -- how do I post my layout?

You will inevitably hear people suggesting a full redo -- Houzz doesn't like stoves in islands. And venting is just one of the reasons. But if you don't want to do that, there are pretty decent overhead hoods that can vent through the roof. And this is possible even if you have cathedral ceilings. I suggest you post both photos and to-scale drawings of your place. You'll probably get better advice that way. Also, let us know what your budget is, what you would like to replace your Jenn-Air with (if that's getting replaced at the same time), and what is important to you when cooking.