I agree with Weissman. I had a friend who had no duct at all. She hired an HVAC guy to install ductwork by opening her drywall, installing the 8" duct between the studs (or was it the joists?) (just barely fit, she told me), and cutting a hole to the outside, including the damper. While it sounds like a big deal, she told me that in the end, actually it wasn't. She was lucky to have an empty soffit above her cabinets, and also did not have a long distance to the outside, about 6'. She says she is so glad she did it. The cost (she was surprised it wasn't so much) and any aggravation are long forgotten, but meanwhile she will have years of enjoyment from cooking with her hood and good ductwork. Of course it depends on each home and its setup, but you could at least look into it.

Exposed ductwork in an older home can be quite charming. It gives it an evolved over time feel. Or, it can be hidden within the cabinets. Either way, it will have to go straight up and then left to go out of the building. I'd do at least an 8" duct, as that gives you more versatility than a 6" duct. 6" limits the possibilities down the road. Doing 8" now instead of 6" won't increase the cost but a couple of dollars, and you could possibly do a higher BTU stove and vent at some point if that interests you because the infrastructure would already be done. [Modern Kitchen[(https://www.houzz.com/photos/modern-kitchen-ideas-phbr1-bp~t_709~s_2105) by Dallas Architects & Designers Domiteaux + Baggett Architects, PLLC [Modern Kitchen[(https://www.houzz.com/photos/modern-kitchen-ideas-phbr1-bp~t_709~s_2105) by Fairfax Kitchen & Bath Designers Kleppinger Design Group, Inc. [Contemporary Kitchen[(https://www.houzz.com/photos/contemporary-kitchen-ideas-phbr1-bp~t_709~s_2103) by Chicago Kitchen & Bath Designers Steve Bailey - Amish Custom Kitchens [Eclectic Kitchen[(https://www.houzz.com/photos/eclectic-kitchen-ideas-phbr1-bp~t_709~s_2104) by Denver Interior Designers & Decorators Momoko Morton

The hood's width at 6" wider than the cooktop is ideal, but many people have the hood the same width as the cooktop, and it's fine. Often people don't want to give up the 6" of upper cabinets, or cannot, because the cabinets are already there. If you have the space for a 42" wide hood, it would be the better choice, but is not an absolute requirement. The thinking on hoods has moved somewhat from emphasizing the width of 6" wider, to more emphasis on the depth of the hood front-to-back. Many hoods sold these days are only 20" front-to-back, leaving the front burners uncovered. That is more of an issue than ensuring extra width on the hood. Find a hood that is close to 24" front-to-back if you can. The height of the hood is ideally 30-36" between the top of the cooktop and the bottom of the hood. If you install higher than that, you are allowing too much space for smoke and grease to escape and float around the kitchen. Go lower than that and your cooking area will feel cramped. I want to reiterate what Stan Z said about the correct ducting. You can have the best hood in the universe, but if your duct diameter is too small, your hood performance will be constrained. Most hoods require 8" or 10" diameter - the specs will say which. You can find hoods with specs for 6" diameter, but those hoods will be noisy, as air is pulled through a more narrow space. 600 cfms is usually enough for most people with a 36" width cooktop. Underpowering the hood is a mistake - you will have spent all that money on the hood, and it will be inadequate from the get-go. If you are thinking about going with more than 600 cfms, the advantage would be that you can run the hood on a lower speed setting most of the time, which will be quieter. The disadvantage of more than 600 cfms is that may require make-up air depending on your locality, building code, and how tight your house is.

I suggest that the capture area is defined by the inner edge of the hood bottom where the flow rate is established (should be established) to handle the highest steady-state cooking plume conditions. The zone between the inner and outer edges can be considered partial capture area as the flow conditions there fall off at a rate dependent on the thickness of the hood edges. That is, the outer boundary is part of the capture area for low plume velocities, and the inner boundary is the limit of the capture area for high plume velocities. (Note that real plumes have varying velocities over their conical shape so generalizations made here are not absolute.) The "sump" as defined above that we have previously called the capture volume is the volume between the plane defined by the hood bottom edge and the lower surface of the baffles. This volume helps "smooth out" transient plume effects, such as suddenly uncovering a frying pan, or throwing wet meat into a hot wok. The minimum desirable size of this volume is determined by cooking conditions, but for many this volume need not be very large. Nonetheless, like other hood aspects that are generally informed by commercial hood design, larger can be deemed better than smaller -- performance wise.