Nailor Product 0722 Ceiling Dampers are for use in round applications, in lieu of hinged door kind dampers in any UL/ULC flooring/ceiling or roof/ceiling assembly with as many as a 3 hour fire resistance score where by air ducts are permitted. Versions 0110DOW, 0120DOW, 0110GOW and 0120GOW are "outside of wall or floor" integral https://dampersforindustrialsecto34566.liberty-blog.com/37188221/heavy-duty-stainless-steel-damper-manufacturers-an-overview