The 2021 edition of the International Energy Conservation Code (IECC) has added a new leak testing requirement for ducts located within the thermal envelope. Previous editions had exempted such testing for those locations. The new requirement will appear in the IECC, and also in Chapter 11, Energy Efficiency, in the 2021 Edition of the International Residential Code (IRC). The purpose of Chapter 11 is to provide minimum design requirements that will promote efficient use of energy in buildings. Keep in mind that duct leakage testing is not a requirement in IRC Chapter 16, Duct Systems, which covers materials, construction, installation, insulation, sealing, ...