With that information, I'm confused too. My guess is that the two sets of information are using different terminology. My guess from the wording is that the Prestige has a smaller aperture than the ModernAire, and that it is smaller than you want, but I can't be certain. I also don't know how the words liner and insert are being used in your last paragraph; often these are used interchangeably to mean a hood without a fancy exterior that is to be covered by a cabinet. Because I don't have either of these, I can only write generically. For clarity (and this may only apply to this message), let me call the size of the hood or insert aperture along the long dimension of a cooktop the length, the size transverse to this along the short dimension of a cooktop the width, and the vertical size between the aperture opening and the duct interface the height, just like one might describe a cardboard box sitting on the ground. Choosing a length of 42 and width of 27 inches is good. Smaller will in many cooking instances lead to more leakage of effluent around the hood. Height is helpful, but of secondary importance to capture and containment except that short heights probably lead to increased pressure losses at the duct transition, thereby slightly reducing the actual cfm from a given fan. Powerful is not the correct adjective for the question of 24 vs. 27 (or vs. 16). The larger the hood for the same fan/blower, the lower the velocity at the aperture, and hence one could use the term in a way that larger was less powerful. Larger would, however, be more effective. In any case, the rated cfm should increase with aperture area to have the same effectiveness in containing rising effluent at the higher velocities that some cooking can achieve. One doesn't want to put a liner high in the wood cabinet that is forming the exterior of the hood. All wood exposed to grease should be protected by metal, both for cleaning and safety. I would want the aperture of the insert/liner to have a lip at the bottom that overlapped the wood. But if this wasn't included, I would want to have strips fabricated at a local sheet metal shop that I could apply to the wood edge. The aperture of the insert (which should be the counterpart of the interior of a standard hood), must fit to the baffles in a way that precludes inducing effluent from "reflecting" out of the hood (plume spillage). The sides can taper, and the baffles can be installed over a range of tilt angles, all of which can make the baffle sizes vary from one hood to another. So, in order of action in the capture and containment process, start with a large enough aperture then ensure sufficient actual cfm at full power. This second step has to account for all the issues you have seen discussed on reading every GW hood thread. (This by itself should merit some GW reward for patience.) kas

Thanks for help. FWIW, the distance from concrete soffit to floor is 7 feet as expected. I have narrowed it down to either Zephyr or Kobe insert liner as both have the horizontal vent in the rear. The horizontal attachment will be moved slightly to the left as that will be where the new cooktop will be moved. I am assuming that there will be some kind of attachment to the current opening which vents to the building's venting system - whence it goes after it leaves my kitchen I have no cares as long as it passes inspection. I am not familiar with either of these brands - does anyone have any recommendations as to one or the other. My venting needs frankly are minimal as I don't deep fry and will have an induction cooktop. I am considering mid range in each brand: KOBE CORE COLLECTION - This retails for about $850. It's ADA compliant with a remote which seems like it would be more convenient than reaching for controls under the cabinet. Monsoon I Insert Monsoon I takes one-piece liners to the next level. Includes dual-level halogen lights, and ADA-compliant wireless remote control, 6-speed electronic controls and either a powerful 600 CFM blower (30″ and 36″ models) or 1,200 CFM blower (42″ and 48″ models). ACT™ available on all models. Vertical and horizontal Zephyr - I couldn't find any functional difference in these two models except one has slightly higher CFM but I am sure the lower would be perfectly adequate for my needs DELUXE IN26 SQB-650-5A BUILT IN / INSERT 30" - 36" 700 CFM $803.49 PREMIUM IN2630SQB-700-2 BUILT IN / INSERT 30" - 30" 750 CFM Build.com $771

1) While it may be possible in the future, having an automatic vent that runs based on temperature at the hood, or current into the cooktop, or some other parameter will not be as sophisticated as setting the flow yourself. For example, you may with to keep the hood off in the winter when only boiling water; the added humidity may be useful. Conversely, simmering bacon should be done at a higher blower level so that the baffles can function correctly and remove the larger end of the grease particle spectrum. 2) Noise is best addressed using a remote (attic or roof) blower and an intermediate silencer such as Fantech makes. Also, a more powerful (and larger) blower operated at part speed will be much quieter than a smaller blower on full speed. 3) Your hood should be at least 42 inches wide and not less than 24 inches from the wall, and preferably this should be the capture area and not the external hood dimensions. With an area of 3.5 ft x 2 ft = 7 sq. ft., say, the necessary volumetric flow rate is 7 x 90 = 630 CFM. To achieve this flow rate in the presence of pressure losses, such as the baffles and imperfect MUA, a blower rated for 900 - 1000 CFM in free air (zero static pressure) should be used. (My 10 sq. ft. aperture hood with 1500 rated CFM roof blower and Fantech silencer is quite modest in noise level on full power. Actual CFM measured under the hood is in the ball park of 1000 to 1100 CFM.) 4) The standard filters for high performance hoods, both commercial and residential, are called baffles. They force the rising air to make two 180-degree turns before entering the hood interior space and thence the duct to the outside. This flow centrifugally ejects grease onto the baffles. Other kinds of specialized filters exist, mainly for commercial purposes. The mesh filters use impingement grease collection, are easily gagged by lint and grease, and need cleaning at short intervals. Baffles can go uncleaned (ignoring aesthetics) for a long time without degrading their filtering or changing their pressure loss. Baffles will have lower pressure loss per unit of area. Mesh filters may be better at collecting grease when the air flow is inadequate for serious cooking. 5) Make-Up-Air must be designed to return to the kitchen the quantity of air that is removed by the hood system, in this case 630 CFM. How well it does that will determine whether 630 CFM is actually achieved, and whether the house pressure falls too low for safety if there are combustion appliances taking air from spaces connected to the kitchen volume. We can discuss that further, but suggest you do a search here on 'hood' and 'MUA' for many many threads that address the particulars.

First is capture, and this requires plume overlap by the hood. Now it is true that plume divergences vary with different factors, but all need to be overlapped, and few hot grease plumes will stay inside the boundary of the cooktop width except those from the center hobs. Capture is not ameliorated by a lower BTU level at the cooktop surface. Second is containment. This performs the removal of the captured plumes from the hood entry volume and expels it outside. To avoid reflections on the sheet metal, or at least to contain reflections, a minimum velocity of hood air is needed to entrain the plume elements into the hood flow to get them through the baffles. This varies with the velocity of the plume components (which varies with the heat input to the pan and whether combustion heating is being used) as well as hood design. So the CFM required for, say, steak searing will be slightly less with induction than with gas, and it might be possible to get away with a nominal 60 CFM/sq. ft. of hood instead of 90 CFM/sq. ft. I would expect that this would still depend on just how hot the searing was, whether the flame was on maximum or we are mostly dealing with a very hot cast iron pan with lowered flame, and how well the hood entry volume (reservoir) was able to average the initial grease vapor transient from throwing the steak into the hot pan. Without computational fluid dynamics evaluation of a particular case, or schlieren photography of the physical hardware in action, the best I can do is generalize. I have 90 to 100 CFM/sq.ft. and can capture induction wok cooking and induction searing effectively, but the transients are somewhat modest, and my hood is very long with some advantage in reservoir volume. So I know it works for me. What I can't "know" is how every other hood would work for me or for any other cook. Hence, I'll stick with 90 CFM/sq.ft. as a recommendation, with a suspicion that for non-extravagant induction cooking, lower specific flow rates may prove sufficient. Budgets and space are in many cases limited, so avoid having a zero percent solution because the 100 percent solution is unaffordable or infeasible.