Yes, my experience has been that downdraft is mostly ineffective (and I am being polite) no matter how you slice it.

Just curious, why can't you go up? I assume you have 10 to 12 inches of floor joist between the kitchen ceiling and the subfloor of the level above, why couldn't you put a duct in that and send it parallel to the joists out of the house?

Drywall is cheap and can be patched and painted very easily by any worthwhile contractor. If it's a possibility, go through the ceiling and straight out the side.

Our kitchen walls and ceiling were like Swiss cheese when we did our remodel. Scary how fast they put it all back together.

-Stooxie

you can have all three :
a big catchment / capture canopy overhead over the cooktop, and
a big inline motor (ie.e. remote) and
ducting traveling down the interstud cavity of the wall, down into the crawlspace.

see my two posts in the general thread about Hoods.

Here is a link that might be useful: ducting Downhill inside a wall is childs play

Stooxie's solution can be a good one. If there is some reason to preclude it, such as where it would end up, is there any way to take a hood and duct it to the crawl space? While there is some pressure loss at each bend, a suitable in-line blower should be able to make up for it and aid the blower, if any, in the hood.

kas

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.

Can you post a sketch? Even if the kitchen is in the middle of the house you should be able to reach an outside wall even if there is a stairwell involved. There are several engineers who regularly post to this site and one of them may be able to offer you a solution. In our case we ripped the entire kitchen ceiling out and moved the electric boxes where we wanted them. Then we replaced the ceiling with plywood and installed a tin ceiling over it. I used the option to use small screws to install which came in handy when we got our CC range and switched from a crappy recurculating hood to a vented hood. I simply unscrewed the affected sections of tin, cut the hole for the 8" duct and replaced the sections. I agree, sheetrock is cheap, rip out as much as you need to and replace and retape it. Don't worry about the texture, scrape it all off. Texture was developed to cover shoddy workmanship. Smooth ceilings are classier, especially with crown moulding, they are easier to clean too. As long as you prefer electric, do look in to induction. I am a gasser myself, but if I had to go electric I would go with induction, it is as much above smooth or coiltop electric as open burners are above sealed gas burners.

I would listen to Davidro on this one. The folks who came to your home were probably right. This has nothing to do with drywall, but with the ceiling joist direction. Unless you can run the ducting in between the joists and have it go to an outside wall you will have to go down.

The only exception would be if you have high ceilings, then you can run the duct across the ceiling and suspend a second ceiling below the duct work. And you can use rectangular ducting and maybe only lose 6 inches of ceiling height.

However, if that's not possible, and the range is against a wall, just install whatever hood you like and run the duct inside the wall between the wall studs- going down. Again it will be rectangular ducting, probably 10x4 inch(or have it made to fit the space as David suggested). Once you hit the crawl space just send it outdoors like it was a dryer vent- of course it has to come out above ground.

Ok, so now that we've determined that the downdraft is the sensible way to go (sorry Caddidaddy, your way seems pretty involved, and the run to make that happen would be very very long and end up exhausting on the front of the house) what have you peeps done with your OTR Microwave situation when you've replace your OTR with a hood? Where did you put your new micro? I want a convection/micro combo. There is no option of replacing any upper cabinets with deeper ones to hold the micro, I don't want it in lower cabinets, so it seems as tho' this only leaves the countertop as an option. I realize the telescoping downdraft thingie is an option and would thus leave room above for an OTR micro, but that solution causes TWO new cabinets to have to be built to hold separate cooktop and wall oven. I would really prefer a stand-alone or slide-in range below the new undercabinet hood.
Thanks for all of your really speedy replies.