A friend of mine works at an architectural energy firm, and he says it's very important in designs that airflow tends towards the kitchen rather than away. The

A friend of mine works at an architectural energy firm, and he says it's very important in designs that airflow tends towards the kitchen rather than away. They do mostly commercial, but I could see it applying to residential as well, and sounds like that situation has, even with the vent hood on, the airflow "upside down". When I was remodeling our kitchen we went with a over range microwave because there really wasn't anywhere else to put it. Those are known for fairly poor airflow. We got a KitchenAid with some of the best available airflow, 440CFM IIRC, but stand alone hoods can do much better. I still have a todo of replacing the roof vent with a larger one, so there's probably still some restriction in there that's slowing us down. You might want to look for similar.