I suspected it may be a Dacor downdraft as it is the only manufacturer that expressly says that its downdrafts are designed for behind a full range. Of course they say they are only for behind Dacor ranges, perhaps this is to encourage purchase of their ranges or to prevent any liability issues, or both. I do wonder if it would be difficult to find an installer/contractor who would install a Dacor downdraft behind a non-Dacor range.

Quick reply to Jenn Air delima. Same problem here. Need to replace our Jenn-Air stove temperature does not heat anymore. Our concern is also with the downdraft. My husband called Home depot and they have one that is a General Electric model, less than $1,000 with down draft. Should hook into our other one vent possibly. Also Sears. we're going to go check it out today

a false beam is a good disguise. We cannot say if it matches the rest of the house. If the galvanized steel ductwork has to be tacked on to the ceiling, then any dropped ceiling, or dropped section, or soffit-looking thingie, or beam-looking disguise, is a good way to cover it. You can paint it too. You can wrap it with anything and call it done. It's definitely a problem to work around. In your second post, ramica, you mentioned a 2 inch gap. I think this is a better problem to work around. I think this is worth a lot more attention. My hunch is that a good answer is somewhere here. If the ceiling is not a concrete slab, it is made of joists, and is almost entirely hollow between the joists. The direction the joists go is the same direction that your ugly metal duct can go, too, for the first few feet. It might not matter at all if that direction is perpendicular to the direction you want. When the duct nears a wall, a transitional piece of ductwork can turn the air stream 90 degrees. This transition piece matches up to a run of standard size duct work that travels along the wall-ceiling junction (which can be covered by a soffit) over to the exterior wall hole where the duct is to go outside. http://en.wikipedia.org/wiki/Soffit ....formed as a ceiling .... fix underneath .... underside of any construction element "boxing it in and painting it white" is a soffit. In a kitchen a soffit can become the place for pot lights directly overhead of the workspace (countertop). So, this is worth considering. A 3.5" by 10.5" rectangular duct is the right size for a flow of air much smaller than your 600 CFM flow. A 3.5" by 10.5" rectangular size of duct is good for rental apartments with electric coil stoves and cheap exhaust hoods. ( ... "I am told the ductwork should be 3 inches high by 10/12 inches wide." ...) A 600CFM stream will need a larger duct. The right duct size is specified by the manufacturer. It will be in their product's PDF on their web site. What size round duct is it? I'd say 8" is my guess. It could be another size. Transitioning to an appropriately sized rectangular duct is easy once you go get the right information. Snoonyb posted in the first reply you got in this thread, asking about joists. Your answer was the wrong one. The next post from someone was from loves2cook4six who asked the same question that snoonyb asked, although the question was worded SO differently that it might appear to be unrecognizable. Then you mentioned a new beam, going the other way from the joist direction. I believe there is a way to go through the support beam "from the addition" even though it is running the wrong way. In the remodeling forum you will get experts telling you how to reinforce a beam in such manner as to allow you to cut a hole through it. I believe there is a way to send the duct through the empty space above the new beam and between the joists. This may be the optimal path of study for you today. Remember that the new beam is perpendicular to the set of joists in the ceiling, and it does not fill the empty space that is still there and just as much available as it was before the new beam arrived. Hth

The only "approved" approved induction setup that would let you vent out is the Dacor range with the matching popup downdraft. You might get another combination to work, but it could be difficult to fit the popup especially if this isn't an island application (which it sounds like it isn't). Your existing range is probably dual fuel (I don't think JA ever made all-gas downdraft ranges) so you would have a 240 line for it. It's definitely an option to consider if you haven't already. However, it's a personal preference. If you prefer to cook on open gas burners, I wouldn't give that up just to vent out, if all you're going to get is mediocre (downdraft) ventilation anyway.