US lawWashingtonRegulationsTitle 296 — LABOR AND INDUSTRIES, DEPARTMENT OFChapter 296-150C — COMMERCIAL COACHES296-150C-1520WAC 296-150C-1520WAC 296-150C-1520. Air ducts—Duct and plenum insulationLast amended: 2005Year: 2026Length: 22 wordsOfficial source Every heating and cooling duct and plenum must be installed according to the International Mechanical Code and the Washington State Energy Code.PreviousWAC 296-150C-1510NextWAC 296-150C-1530