Underwriters LaboratoriesUL 181AStandard for Closure Systems for Use with Rigid Air Ducts.Referenced across 3 Anvilfield field guides. Field guides that apply UL 181AHVACHVACDuct leakage testing field guideHVACDuctwork types field guideHVACSheet metal duct fabrication field guide Often cited alongsideASHRAE 90.1IECCSMACNANFPA 96ASCE 7NFPA 90A Browse all codes and standards