Oh, I think I see looking at your inspiration picture in the other post, you're talking about what I think is called a Mantle range hood. Is this the sort of thing you're talking about: I would image how far recessed the insert is inside the hood depends on the design of the hood, but I don't really have experience with them.

I am in the process of researching a range hood insert for a 30" dual fuel range. I will need 600 CFM's. It will be vented out of the back towards our driveway, so I do not want an external fan. Recommendations needed.

If you like reading, you have come to the right place, because we have a large number of hood related threads that can be read for as much theory and practice as you can stand. There are at least two suppliers of recirculating hoods with sufficient filtering that they might quality as at least marginally effective (from my purist point of view). One is Vent-a-Hood and the other is (as I recall) Best by Broan. There may be others and I hope those here who have or know of them will pipe up. Searching the manufacturers' web sites should provide specific information. Good quality recirculating hoods will have a succession of filters to remove grease and odor. CFM can be determined from the hood aperture area, and we don't yet know what size hood you may choose from among the limited number of recirculating hoods. For example, for a 2-ft front-to-back by 3-ft side-to-side aperture (6 sq. ft.) to achieve a goal of 90 ft/min across the hood aperture would require 540 CFM. Actual blower rating has to be higher due to pressure drops, but these may be accounted for in how a given recirculating hood is specified, so the usual factor of 1.5X that I suggest to make up for this may not be needed. Also, recirculating provides its own make-up air, so that factor is not applicable. I'm assuming that there is a good reason for not attempting to duct the cooking effluent outside. Duct installation may range from easy to extremely difficult, and without knowing more I won't attempt to provide encouragement for adopting the superior approach of external exhaust. kas

Hi there! While it isn't the most common, there have been times we have made a very long/large range hood and only need a certain size insert (for example 10' wide hood, only needing a 48" liner), so most often what we would do is install a stainless steel panel to allow everything to look smooth and coherent with the liner. Some people opt to add lighting to the "dead" panel space, and I would definitely recommend making sure you get the proper CFM for your space, but yes you can have an insert smaller than the range hood. Hope this helps!