If a greater hood height allows more volume below the baffles and still provides good path clearance above the baffles to the duct, then there is a potential capture advantage at lower cfm rates. If the volume below the baffles is the same in each unit, and the baffles are the same, and the space above the baffles is adequate for the flow, then it is an aesthetic issue. One wonders, however, why eight-inches of extra stainless steel only costs $50 more. kas

Hopefully you'll get some specific advice but I have a suspicion that all you can really do is check looks, size, and CFM and hope for the best. Since you can't really tell in a showroom how noisy they'll be because they aren't ducted properly, you CAN check things like how easy it is to remove the thingies to clean, how good the lights are, how likely it is that knobs will fall into the pot, and stuff like that.

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.

Howdy, sorry for not responding sooner. I guess I'm not configured to forward the email notices. In regards to opaone's comments: Not sure what you might mean by a "real hood", but if it's a restaurant quality super duper hood - then no. The kitchen is tiny and unless I blow out an exterior wall it'll stay that way. The current hood is a standard 30" affair; it's only redeeming qualities are the nifty LEDs I installed and the 7" exhaust going out the top. The presence of so many 90° bends is exactly why I'd like to make a direct shot to the roof. What a horrid design! In regards to Austin Air's comments: The 5" space will easily fit the 11" x 3" oval (6" equivalent) duct I was planning on using. The furnace space is sealed and takes its make-up/combustion air from vents leading to the attic, which is ventilated through soffit vents and a large roof-mounted mushroom. Kitchen make-up air is currently not too much of an issue as the house is a "leaker" - I have yet to replace all the aluminium windows and sliders, but will surely install a vent/control/device to address make-up if/when I go with the through-the-roof range vent. What I'm leaning towards now, after posting this and asking around, is having my furnace replaced before doing the modification. I don't want to go through the work and then have Mr./Mrs./Ms. City Inspector Man/Woman/Person question the duct passing through the furnace closet. Another advantage would be the additional physical space gained by replacing the 1970s dinosaur-air-heater with a modern high-efficiency unit. They're so small now!! If I had me a moneytree, I'd plop a horizontal unit in the attic and solve all kinds of issues.