Many here say it's advisable to get a hood larger than your cooktop, but many others of us, like me, have hoods the same width as our cooktops/rangetops and it works fine. If your cooktop is up against the wall with uppers to each side, that will help funnel everything to the hood...if over an island or is otherwise wide open above the cooktop, it could be nice to have a wider capture area. --I'm not an expert on CFMs. 600 sounds reasonable unless maybe you're going to do an unusually large amount of meat-searing, deep frying, or stir-fry. Might be fine then, too. I had 525 CFMs in our last house, and felt it was OK, but sometimes could have used more power.

Ventahood makes 12" inserts. :) Here is a link that might be useful: Ventahood Inserts

Bertazzoni > XO, any day of the week. The difference between Italian and Chinese quality is generally pretty self-evident. Re "too much CFM" - not necessarily. You probably won't be running it at the highest speed all the time; just because your car can go 160 MPH, doesn't mean you'll be hitting that on the way to the grocery store.

vinmarks No, in your case I was tempted to write that the VaH can make use of that size duct. I think VaH may be negligent if they don't point out that that duct size needs to be matched on the MUA side. As pointed out earlier, few in the kitchen hood sales chain want to raise the issue of make-up air and the horror it can be to retrofit into a renovation.* But lest others think that they need 12-inch duct for 1200 CFM with conventional blowers in lieu of using 10-inch for typical lengths, I wanted to point out that that would be only a modest improvement relative to getting the MUA in with low pressure loss. Pressure loss is counted from the cooktop to outside and then from outside to inside back to the cooktop. ------- *An example MERV7 high flow 4-inch deep pleated filter, 2 ft x 2 ft in area used to catch the big particles and bugs that the MUA air could pass into the house, used at 1200 CFM (300 ft/min) would have a pressure loss of 0.1 inches w.c. (See table from https://www.texairfilters.com/comparative-tests-on-pressure-drop-of-hvac-filters/ If one looks into VaH data, for example see below, 0.1 inches w.c. drops the flow rate of a dual blower (1200 CFM) hood to 1060 CFM. At 1060 CFM, the filter pressure loss is a bit less, so one really needs to plot filter loss vs flow rate against the fan curve implied by the data below to obtain the expected flow rates (excluding ducts, MUA register, and exhaust duct cap pressure losses which also need to be counted) . And for comparison, using an equation I found on the Internet at the HVAC engineering forum referencing the 2003 ASHRAE Handbook at Page 52.5 (confirmed in my copy) and adapting it with some trepidation to screening as was done at the forum, and assuming a screen of 70% openness across a 12-inch duct at 1200 CFM, the pressure loss is even higher than the pleated filter, reaching 0.7 inches, w.c. With a 15-inch screened duct, 0.1 inches w.c. at 1000 CFM could be achieved. The moral is, use a lot of screen area, or low loss filtering, or let the sparrows in.