As a primary regulation, decide 100 cfm for every direct foot of meals preparation floor space. For professional-style ranges, the system is 100 cfm for each 10,000 BTUs your machine places out. Varied different components come into play as nicely. For every three inches a hood goes past the beneficial peak above the cooktop, add 100 cfm. Island hoods want added cfm to make up for cross drafts, so calculate 150 cfm per straight foot for typical cooktops; add a further 100 cfm to the pro-range estimate. And likewise think about simply the way you cook dinner. In case you not often grill or stir-fry at excessive heat, you’ll have the power to go for a decrease cfm than prompt.