We're in the throes of designing a new kitchen (actually, a modification/update of the existing kitchen is more accurate). I have vowed to get rid of my totally useless pop-up downdraft exhaust fan and replace it with an overhead exhaust. This is not as simple as it sounds because the island is in the middle of the room and there's a room right above it, so it can't be exhausted straight up and out. In fact, because of how the joists run, it's going to require four separate bends of the ductwork in order to accomplish this.
We'll rely on the advice of an HVAC expert to design an efficient exhaust system, assuming it's even possible. But I'd like to hear from anyone else who has experience with this kind of situation. How large (diameter) does the duct have to be? How powerful does the fan have to be? Should we consider putting the fan on the end of the system, rather than on the end where the hood is? Is such a design even feasible -- that is, after going through considerable expense, will it work efficiently? How can I make an informed decision about this? Thanks!