By careful measurement of wall distances over a path from one side to the other of the duct wall, it should be possible to determine the thickness of the wall. If it is a standard 2 x 4 stud wall, the cavity is 3.5 inches; if a less standard 2 x 6 wall, then the cavity is 5.5 inches. Neither of these will accommodate a 6-inch round duct, so transition to rectangular is likely. The third possibility is a double wall built to accommodate the round duct. It should be possible to distinguish these even with modest error in measurement. kas

There will be some repair work that will have to be done to the wall to run the duct work if you install a vented hood. Without too much more work the stud could probably be moved. A header would need to be installed to carry the load of the stud, just as would be done with any doorway or window. So I guess it comes down to what amount of work the vented hood is worth. I definitely agree that the downdraft would be better than the non-vented hood. The other thing to consider is the fact that adding 2 more 90 degree turns and the extra ducting is going to diminish the effectiveness of the fan. With that length you may need an in-line fan installed to boost the power. Your appliance provider should be able to help you figure out what you need for the amount of pipe you have. Jesse Pender

I happen to be collecting pictures of vent hoods that don't go to the ceiling. So here you go: https://www.houzz.com/photos/mont-albert-hampton-style-overlay-kitchen-transitional-kitchen-melbourne-phvw-vp~11375968 https://www.houzz.com/photos/museum-district-1st-floor-renovation-contemporary-kitchen-richmond-phvw-vp~37938785 https://www.houzz.com/photos/kitchenette-beach-style-kitchen-portland-maine-phvw-vp~420400 https://www.houzz.com/photos/realisation-bulthaup-b3-contemporary-kitchen-brest-phvw-vp~36424410 https://www.houzz.com/photos/contemporary-eco-kitchen-in-the-cotswolds-scandinavian-kitchen-phvw-vp~26626265 We are still building (and are not as far along as you are) but I'm planning a K series vent-a-hood that rear vents right out the back. It will be in a wood box, the idea is to have it more or less disappear. (We're pairing it with an induction cooktop.) I know it's a little under-powered compared to some of the vortexes out there, but I think we'll be fine with it.

Thanks for the response. I would think the CFM has just as much to do with the motor / blower as it does with the diameter of the duct. It's not like you can't push a larger volume of air though a smaller opening given the right amount of pressure. Anyways, here is the 900 CFM insert we are considering with recommended 6" ducting: https://www.prolinerangehoods.com/46-proline-pljl-wall-range-hood-insert-15-deep