Prescriptive and performance-related requirements are used to establish minimal regulations for mechanical systems. The IMC was created using broad-based concepts that allow for the adoption of new materials, technologies, and designs. The following are significant changes in the 2021 IMC: Clothes dryer exhaust terminals must be at least 3 feet away from any building opening. Spray-applied polyurethane foam on the exterior of ducts in attics and crawl spaces to fulfill certain smoke and flame index limitations. Fire and smoke dampers require authorized access for inspection and maintenance. New refrigerants have been added to the refrigerant tables. Condensate termination identification markers and discharge limitations have been added. Combination intake/exhaust terminations approved by the manufacturer are permissible, easing the separation requirement. Minimum mechanical ventilation for whole-house balanced ventilation systems is reduced by 30%