mechanical systems using prescriptive and performance-related provisions. The IMC was developed with broad-based principles that make possible the use of new materials, methods and design. Important changes in the 2021 IMC include: Clothes dryer exhaust terminals required to be at least 3 feet from any opening into a building. Polyurethane spray-applied foam on the exterior of ducts in attics and crawl spaces required to meet specific smoke and flame index limits. Fire and smoke dampers must be provided with approved access for inspection and maintenance. Refrigerant tables updated to include new refrigerants. Addition of condensate termination identification markings and discharge restrictions. Approved factory-built combination intake/exhaust terminations permitted, relaxing separation requirement. 30% reduction in minimum mechanical ventilation for whole-house balanced ventilation systems. Continuous operation requirement for manicure and pedicure station exhaust systems. Grease duct horizontal cleanout required within 3 feet of a horizontal discharge fan.