Which standard must tapes and mastics used to seal metallic flexible air ducts comply with?

The correct answer is that tapes and mastics used to seal metallic flexible air ducts must comply with UL 181B. This standard specifically addresses products designed for sealing and joining duct systems, including flexible ducts, in HVAC applications. UL 181B focuses on the performance requirements for materials that come into contact with air moving through ducts, ensuring that they can adequately maintain their integrity and effectiveness under varying conditions, such as temperature and humidity.

By complying with UL 181B, the tapes and mastics demonstrate their ability to resist air leakage, maintain adhesion, and withstand environmental stresses, which is essential for maintaining the efficiency and safety of HVAC systems. This ensures that the sealed connections do not contribute to energy loss or system inefficiencies, which are critical factors in air duct performance and indoor air quality.

Standards such as UL 181A, while also addressing duct sealing materials, specifically pertain to products that have different performance criteria or applications. Understanding the distinctions among these UL standards is crucial for selecting the appropriate products in compliance with building codes and industry best practices.