What's the big deal? Not much more than a few bucks and a few minutes of labor separate the two. Anyway, I'm not antss or guadalupe, but I'm still capable of googling International Residential Code. As I posted on another thread: M1503.1 General. Range hoods shall discharge to the outdoors through a single-wall duct. The duct serving the hood shall have a smooth interior surface, shall be air tight and shall be equipped with a backdraft damper. M1503.2 Duct material. Single-wall ducts serving range hoods shall be constructed of galvanized steel, stainless steel or copper. Local code may prevail and allow non-smooth aluminum ducting, but that doesn't mean it's better.

Differential means the difference between the outside temperature and the temperature you want the MUA to be (warmer or colder than outside). CFM means actual hood CFM, and the actual hood CFM will never exceed that provided by all the sources of MUA CFM available at the kitchen. If the differential pressure is zero, then one has perfect MUA (pressure balance) and the hood will only be "gagged" by its own baffles, transitions, and ducting. The achieved indoor-outdoor differential pressure won't generally be zero, but it can be kept modest relative to changes on the fan curve. Aim for 90 hood CFM per square foot of hood intake aperture. This should provide complete containment for most cooking for captured plumes using residential hoods with baffles. (Plumes are initially captured if the hood aperture overlaps them.) So, for a desired/required 800 CFM, say, one finds 800 on the abscissa and goes up to a differential temperature curve representative of an outdoor and indoor temperature difference, and thence left to the ordinate where the BTU/hr needed is listed, based on the specific heat of air and the mass of air being moved at that CFM. BTU/hr has a counterpart watts value for electric heating, and also a tons of air conditioning value if one intends to cool. Conversion factors may be found by use of an Internet search engine.

Broan/NuTone/Best make a large range of ventilation equipments and generally you get what you pay for as far as I can tell. However, why a "high end" appliance dealer wouldn't include some other brands is unclear. At a minimum, I would expect a Wolf dealer to have examples of Wolf hoods. (My hood is a Wolf, made by Independent before Wolf moved production in-house.) Decide how high you want the hood for good site lines and reaching to the back burners, and missing one's head, while keeping in mind that the front burners will be emitting plumes that expand as they rise, so height corresponds to increases in needed overlap -- side to side and front to back. 10 degrees from vertical measured from the flame diameters when pans are on the burners can be used for plume expansion estimation. Sketch it out. Given a height and hence width and depth, calculate the square footage of the entry aperture of the hood. For wall hoods the light bar in the front may qualify as partial or whole entry aperture area. Multiply area by 90 CFM/sq. ft. Multiply by 1.5 if you don't know all the pressure losses. Find a blower that has that result as a rated value. Decide on in-hood, in attic (in line), or on roof. Farther away is generally quieter. If there is room for a silencer (Fantech) between blower and hood then the result will be quieter still. There is a lot of dissension about ease of hood cleaning by type. I can say that my Wolf hood baffle assemblies easily remove and can be cleaned in a dishwasher. (I have ten of these, so it takes two loads.) One still wants to reach up inside and wipe the surfaces. I use Simple Green, but likely there are myriad possible choices. I have never owned a VaH, and was initially repulsed (2007) by the Magic Lung® claims. Others like them. If you have guests sitting where they can see into the hood, a baffle system may be aesthetically superior. Duct should be sized so that full power actual flow rate achieves a velocity in the duct between 1000 and 2000 ft/min for best balance between grease condensation and grease impingement. You can go lower (larger duct) if you pre-heat the duct in cold weather. On CFM focus. Standard (if that actually ever applies) residential hoods are designed to fit into residential kitchens. Commercial hoods are designed to fit into commercial kitchens. At a minimum, the typical difference is two feet of ceiling height. When the commercial hood can be built so that there is tremendous volume below its baffles, there are conditions where the specific flow rate (CFM/sq. ft.) can be reduced below the value I suggested above. This is due to "baffle averaging" resulting from the reservoir volume vs. plume steady state and transient volumetric rates. At the other extreme, residential hoods with little volume below the baffles will allow plume escape (capture failure) if the plumes are not immediately entrained into the baffle flow. And, of course, plumes not initially captured are not contained and removed except as a matter of long term kitchen (and whole house) air replacement. So CFM focus varies. Another difference is that commercial hoods are typically operated at a fixed CFM and the MUA is balanced for this case, whereas residential hoods, along with bathroom fans, etc., operate at variable CFM, and this makes the MUA control more complex.

Let me emphasize a comment above: For greasy plume capture the hood has to overlap the cooking area because the cooking plumes expand as they rise. This requirement leads to rectangular hood openings, not circular openings. For examples of island hood sizes, you can review the Wolf Design Guide, available at Subzero Wolf's web site. Also, a tour of AJ Madison will reveal probably hundreds of options, perhaps less expensive. Keep in mind one almost never gets more than he pays for. Flow rates (CFM) to assure containment are based on the same parameters as published here in numerous hood related threads. A properly sized hood with adequate CFM should minimize the need to clean windows and walls behind the hood. Climbing on stone counters, if used, should be avoided in any case.