All hood filtering, whether meshes, baffles, or VAH sling designs, can only remove part of the grease aerosol particle spectrum. This part is that of the larger diameter particles, with decreasing performance through the mid-range. The rest is hoped to be discharged into the atmosphere, but there will be some collection in ducting depending on various factors. The only system I know of that can handle the entire spectrum is the intense UV approach used above commercial perforated ceiling collection designs. Hence, discharge into an attic not only subjects the attic to grease, water vapor, and odor, but could potentially be a fire hazard. Is there a reference somewhere in which VAH specifies that attic discharge is allowed? Earlier, the value 90 was raised. That may have been a misapplication of my expressed opinion on the flow rate (cfm) desirable per square foot of hood aperture to ensure that the 3 ft/s rising effluent from hot sources (griddles, woks, etc) is assured of containment by baffles and meshes. Rules of thumb such as cfm per BTU/hr or cfm per foot of hood edge are derived from various assumptions about the nature of the cooking field. kas

Psyche - I am linking a thread which discusses when the hood is wider than the range, should the backsplash behind the range be the width of the hood or the width of the range. The conclusion seems to depend on whether there are upper cabinets on either side of the hood. If there are upper cabinets, then you should match the backsplash width to the hood width. Otherwise, you will have a 3" sliver on either side of the hood of empty wall between the edge of the hood and the cabinets. Thread Called What Size for Stainless Steel Panel behind Rangetop

I did a search for "hood over island", here's the result. Through the first 3 pages most didn't have pendants, but there are some and it will give you an idea. I personally would go with cans. :)

First, for scaling hood volumetric flow rate vs. whatever, it may be helpful to read the Greenheck Guide, at least to page 12, available at: https://www.tagengineering.ca/wp-content/uploads/2015/02/KVSApplDesign_catalog.pdf. Second, my view is that the Greenheck method best represents addressing the actual physical phenomena, because the BTU method only has an indirect relationship with the plume to be captured and contained. So, with that noted, for capture, your hood should overlap the locus of cooking pan surfaces by enough that at the height of the hood aperture, the plume is mostly captured. Most of the higher velocity portions of the plume are contained within a 10 degree angle from vertical for each point on the pans. A three-inch margin relative to the appliance width is usually sufficient, at least to 36 inches height. A maximum front-to-back distance is recommended, where maximum applies to the sizes of potential candidate hoods available for sale. For containment, the air velocity into the hood aperture has to be sufficient to ensure that all captured plume components are entrained into the air entering the baffles, and none reflects out of the hood (spillage). This depends on the shape of the hood, baffle area, temperature of the pan, and whether hot gas combustion products are also being collected. Because this is mainly affected by the velocity of the plume, and because one cannot shut closed various "unused" parts of the hood, the maximally hot cooking hood flow rate has to be the same whether only one burner is used or all burners are used. (This may not apply to large reservoir commercial hoods.) Hence, we multiply the required containment velocity by the entry aperture area to find CFM. Viz., 90 ft/min desired velocity x 7 sq. ft. area = 630 CFM. This is the actual required volumetric flow for hot cooking conditions on gas such as wok cooking or searing. For valid reasons, not actually requiring cynicism, blowers are rated for zero static pressure conditions and have a corresponding 'fan curve' to define performance when there is a pressure drop across the blower circuit. For kitchens, this circuit pressure drop comprises the pressure loss getting the replacement air into the kitchen -- ameliorated by a MUA system, the pressure loss passing the baffles, pressure losses in hood and duct transitions, and in the exit cap. If the blower is built into the exit cap, then that is usually included in the blower data. When all the parameters of the circuit are not known, it is usually sufficient to acquire a blower with a zero static pressure flow rate of 1.5 times the required flow rate. For the example above, this is approximately 1000 CFM. With the pressure loss of well filtered passive MUA, one might want to go higher to 1200 CFM. With active pressure balanced MUA, 900 might do. It depends on many factors. In any case, for blowers rated for over 400 CFM, MUA is required in most municipalities. A passive duct with damper and perhaps a nice pleated furnace filter may be adequate in temperate conditions. For cold environments, a means of heating the MUA in the duct, or in an intermediate room into which it is first introduced, is needed. MUA should not be introduced into the kitchen in a way that causes turbulence between the cooktop and the hood entry aperture.