I have your same problem but have no option to enlarge the vent duct due to the size of the space between the wall and ceiling studs. My previous vent hood was a 36" Cavaliere 900 cfm for a 36" Dacor Epicure cooktop. My new range is 36" DCS with 6 burners. Because I wanted a more substantial look, and after much searching and debating, I bought an AirPro 860 cfm (link below) The Cavaliere hood was more than what I needed for the 36" Dacor. I never turned it up past 1 or 2 while cooking. On 6, the highest speed, it was kinda loud but since I never used it on high it wasn't a problem. The AirPro has not been installed yet so I don't know what the actual noise level will be but it's rated at 35 / 0.7 to 67 / 6.5 (Lowest to Highest Speed). I just couldn't see paying thousands of dollars for a vent hood especially since my $400 Cavaliere had worked fine for 5 years. During my hood research one of the retailers did tell me there was a vent outlet adapter available online but because our contractor wasn't thrilled with that idea, I stayed with the 6" hood duct. Hope this helps. Good luck in your search for the right hood. Here is a link that might be useful: AirPro Hood

Hollysprings and AngieDIY - Duct has to go through an opening in a brick wall, make a 90 degree turn and then out a second porch wall. Actually 3 90 degree turns in all. Might be able to fit a rectangular duct - but why is that better than round? Hood is only 400 CFM so it's on the wimpy side to begin with. Other option may be to convert it to recirculate instead of vent. Is that better? Would I be better getting a a hood with more CFMs? Wouldn't that need even larger duct work. Range is a KitchenAid - which has one 14,000 BTU burner, one thats is 12500 BTU and 2 that are 6000 each. Left Rear Burner Rating: 6,000 BTU Right Front Burner Rating: 6,000 BTU Right Rear Burner Rating: 12,500 BTU Thoughts? And THANKS!

Ah! you missed one of the versions of a comment I have added to quite a few threads. Here it is again. Because we do not get to close off parts of the hood not receiving cooking plume impact, all of the hood has to flow the amount needed at the most stressing part of the effluent plume to be contained at the hood baffle space. How much do we need? Well the actual issue is what velocity of air has to be pulled past the baffles to ensure that the rising plume is pulled into the baffles and contained, versus reflecting off of the baffles and potentially curling back into the room, thereby escaping the capture area and hence removal by the hood. Hot cooking plumes over gas burners can rise at velocities of 1.2 m/s, or almost 4 ft/s. The baffle gap is roughly half the baffle assembly area, so to entrain the plume flow, it seems that some portion of 4 ft/s or 4 x 60 CFM per sq. ft. of baffle area is needed for good containment. Actually, there is usually space under the baffles larger than the baffles proper, so adequate flow is needed all across the hood capture aperture. I believe that I have about 900 actual CFM at home, pulled through a 10 sq. ft. Wolf Pro Island hood. This is equivalent to 90 ft/s. This works over induction hobs, including searing and wok cooking with a 3500W Cooktek wok hob. As it happens, Greenheck also looked into the requirements for CFM, perhaps like me doubting that 100 CFM per ft. of hood edge had a mathematical connection to the process of cooking plume containment. They have published a range of values, and I have taken the liberty of copying their relevant table below. So take your hood area, multiply by some value you believe in for actual needed flow, then multiply by another factor to account for blower ratings not actually applying to the conditions in which they are used. (Another topic written about here more than a few times.) http://www.greenheck.com/media/pdf/otherinfo/KVSApplDesign_catalog.pdf No one has complained here that aiming for 90 CFM/sq. ft. of hood aperture allowed smoke and steam to escape into the kitchen, so long as the hood overlapped the cooking area by enough to capture the expanding plumes.

Melody, I'm a licensed mechanical contractor who specializes in kitchen ventilation. Your photo suggests your cooking area will back up to an exterior wall. Some hoods, but not all of them, feature the ability to rear vent vs exhausting out the top (Or immediately out the top, into the cabinet above, then out the wall) So could be mounted under a cabinet as you wish. Providing for a wider hood to facilitate vapor capture, as has been suggested, is a smart approach. A 36" hood over a 30" cooking unit looks cool, too. However, anything in the path of the duct, regardless if it's within the wall &/or on the exterior of the wall will have to be modified to provide clearance for said duct. Period. And remember hoods under 400CFM are not high-performance units. But hoods over 400CFM require make-up air be provided. Not a DIY project. Pull a permit. Good luck!