In take vents(soffit) and attic vents are a system that should be balanced. The size of the attic dictates the exhaust vent size and that designates the intake vent size. It can't hurt to have more intakes then is required. I've seen soffits where the entire run is ventilated.Is there a formula or rule of thumb to know how many soffit vents are requires in an attic space? Does every rafter bay at eave line require a vent? Location is in Ontario, Canada.