We built a custom vent hood over our 36 inch rangetop. Problem is the width where the exhaust fan will go is 39 inches wide and 18.5 inches deep. I mostly see 36 inch insert exhaust fans. Do we just build some trim around it to close the gap around the perimeter or is there an additional insert piece i can buy? I did find one exhaust fan that is 39 inches wide but also very expensive. Also what CFM do i need? Thank you
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