This Standard provides a consistent, uniform methodology for evaluating the airtightness of dwelling and sleeping unit enclosures, the airtightness of heating and cooling air distribution systems, and the airflows of mechanical ventilation systems. These test procedures can be used for building diagnostics, for quality assurance and control, for determining compliance with codes and standards, and for determining input to energy simulation models for energy ratings. The Standard recognizes some test procedures are easier to perform depending on characteristics of the unit and HVAC system, and different codes and standards have specific testing requirements. Therefore, the Standard presents several alternative approaches for each measurement to allow flexibility in the application of the Standard. This 2019 edition of the Standard is the second edition and its Scope has expanded to include testing procedures for enclosures and systems of Dwelling and Sleeping Units in buildings of any height.