The fact that you cannot vent externally doesn't change that the heat, odors, grease, steam, and smoke still move outward as they move upwards. They will either deposit on the sides of your cabinets, or into the capture area of the hood. You pick which one by choosing the size of the hood.

Thanks GreenDesigns, that makes so much sense! I have asked various appliance / hood dealers here and have gotten confused by their responses. Thanks for clearing my mind. I so appreciate your response!