We are buying a 36" Bluestar RNB range for our new kitchen. We're going to do a custom hood cabinet and I am very confused about what size insert to buy. I understand it's best that we have a 42" capture area over the range. Is that the width of the insert we need? Or do we need a 40" insert that goes inside a 42" cabinet? There will be cabinetry adjacent to the range.

Bluestar recommends at least a 900 CFM hood. If you have a recommendation for an insert that meets our size and CFM needs, please share. We're getting ready to order cabinets so I need to know what insert we're purchasing so the cabinet maker can build the hood cabinet to fit the hood insert.