Which of the following closure systems is commonly used for sealing flexible air ducts according to UL 181B?

The correct answer is that all the listed closure systems—mastic, pressure-sensitive tape, and heat-sensitive tape—are commonly used for sealing flexible air ducts according to UL 181B.

Mastic is a sealing material that provides a durable and flexible seal, making it suitable for a variety of applications in HVAC systems, particularly where flexibility and movement are expected. It effectively seals joints and seams to prevent air leakage, which is crucial for maintaining system efficiency.

Pressure-sensitive tape is another effective sealing option. It adheres to the surface without needing additional adhesives or tools, providing a quick and reliable method for sealing flexible ducts. It is designed to maintain its adhesion and performance over time in the conditions typical of duct applications.

Heat-sensitive tape, often used in higher-temperature applications, bonds when exposed to certain heat levels, allowing for a secure and strong seal that can withstand more extreme conditions.

Using a combination of these closure systems allows for flexibility and adaptability in various installation scenarios, ultimately leading to improved performance of the ductwork in HVAC systems. This comprehensive approach is recommended in UL 181B to ensure reliable, efficient, and compliant duct sealing.