Field glossarySeal class (A/B/C)What must be sealed: A is everything, B is joints and seams, C is transverse joints onlyUsed across 2 Anvilfield field guides, most in HVAC. Where this shows upHVACDuct leakage testing field guideHVACSheet metal duct fabrication field guide Related termsLeakage class (CL)CLGaugePressure classTransverse joint Back to the full field glossary