Nailor Model 0722 Ceiling Dampers are for use in round purposes, in lieu of hinged door kind dampers in any UL/ULC flooring/ceiling or roof/ceiling assembly with approximately a 3 hour fireplace resistance rating where air ducts are allowed. Google aims to make it easier to continue to be knowledgeable by making use of know-how https://dampers-for-industrial-se01223.bloguetechno.com/the-2-minute-rule-for-dampers-for-industrial-sector-72180377