Needinfo1 - what Tom meant by recessed is a canopy hood. I.e. don't buy one of those flat hoods, even though they look cool. Also, the curved glass ones aren't so great. A canopy hood will capture best the rising smoke and grease. To the OP, a 30" hood will be fine. The hoods that are 36" wide over a 30" hood are the ideal, but so many of us cannot afford to forego the upper cabinetry for the 36" width. You should get a hood that is not a skimpy depth of 20-22". Those won't cover the front burners. As Tom said, a 24" depth hood would be good. Your question about 600 cfm vs. less cfm: it is better to have the 600 cfm, even if you don't use it that often, say, for searing steak, than to have an underpowered hood, and have to have it on its highest setting all the time. You'll have less noise if you can run your 600 cfm hood at medium or low, and still have the hood be effective, than if you are running your 400 cfm hood on high all the time because it is underpowered. Make sure your exhaust duct is sized properly. Most hoods specify an 8" or 10" diameter duct. There are some hoods that allow a 6" diameter duct, but they're harder to find. The problem with pushing too much air through too small of a duct is that you will get increased noise and decreased efficiency though no fault of the hood. So check your exhaust duct size (if already installed), and match your hood to it, or if still in the construction stage, install the right-sized duct.

Was able to get a hold of zline. Issue is production of the chimney. They have none and I was told it would be a long time and to order something else. Was also told the 24" might be okay, but with a 28" range, it really should be bigger. Modernair had great technical support and got back to me right away, with a quote of about $4600 to make something similar to the $1400 zline.

I may have left out some words due to repetition. The number of square feet refers to the entry aperture of the hood. For example, a 36 x 24 hood aperture would be 6 square feet, and would require 6 x 90 = 360 CFM actual, likely needing a blower rated at 540 CFM. Pressure loss not only entails the ducting, but the baffles and the MUA path. Leaky walls are not exactly a free path for air. A leaky house may be sufficient for MUA in practice (given that the blower rating takes the pressure loss into account), but the OP may live where aggressive code enforcement will demand at least a damper in a duct to the outside. The rationale for 90 ft/min is based on ensuring entrainment into baffle gaps that typically are around 50% of the baffle area and have to deal with upward plume velocities of as much as 1.2 m/s. See also the table (Figure 4) on page 9 of the Greenheck Guide available here: https://www.tagengineering.ca/wp-content/uploads/2015/02/KVSApplDesign_catalog.pdf The discussion leading to that table should prove useful for background information. In particular, the Greenheck method vs. the linear feet of hood edge (all the way around for an island hood) method is discussed. (Note commercial cooking rarely is true island type; even located in the middle of a kitchen the hood is connected to the cooktop via a back section. There may also be side skirts on the hood.) Last, let me point out that capture can fail under cross draft conditions, which are almost always worse for island/peninsula configurations than wall configurations.

@Aglitter Thanks for the measurement and sharing your experience from comparing the different hoods. I have looked at Captiveaire but after comparing cost, my local builder for restaurant hoods have better pricing for the basic features I need. Captiveaire definitely has a lot of nice and useful features, if you are willing to pay for (eg. they have filter that can capture 70-80% oil, while regular baffle filter captures less than 50%. But the down side is the huge jump in resistance, so you need a much more powerful blower for it to work). I have been tempting to actually build an outdoor kitchen for my cooking (commercial wok burner!!!!!) but it is just not very practical as Canada is winter half the year..... And what beats the convenience of searing, basting and finishing steak all at one spot while cooking other garnish LOL. I will still have an outdoor BBQ for the smoking and party grilling though. @kaseki I totally missed thinking about the transition between slow flow to the high speed duct flow! I looked a bit and I think I will put something like this at the transition of duct to the containment volume https://www.ecmdi.com/8-spiral-takeoff-with-gasket-82590 Now with all these consideration.... I am thinking may be I should just spend a bit of time and run some CFD models.... even though the thought of modelling the baffle filter is putting me off LOL Also Re: WOK cooking, a single WOK cooking can overwhelm 800 CFM for sure when I am getting the vaporized oil to light for the "wok hei", on my modified bluestar burner LOL