I'm considering having a whole house hepa cleaner installed as a standalone unit (ie, not hooked to HVAC system). One thing I can't figure out is that the unit has 1,000 cfm capability, but the openings on the unit are 10x12 inches. 16 inch flex duct is rated for 1,000 cfm, but it seems like 16 inch flex duct is too big to hook to a 10x12 opening (a 10x12 opening would equate more closely to 12 inch flex duct). Am I missing something? Can 1,000 cfm pass through a 10x12 opening?