i'm losing my mind a little bit over choosing ventilation. what all do i need to know? i need a wallmount, i guess a chimney style since i will have no wall cabinets over the stove. i'm buying a dcs 36" gas range and their website says 600 - 1200 cfm are needed. how do i know which? does that mean that 600 is enough? also, we currently have a microwave hood combo - i think with a roof vent. can we still use the duct and roof vent that we have? i am way over budget already so i am limited in my choices, thought safety and quality are a high priority. uhhhhh! help!