Which standard is applicable for nonmetallic duct construction?

The applicable standard for nonmetallic duct construction is UL 181. This standard specifically regulates the materials and systems used in the construction of air ducts, focusing on performance, safety, and durability. UL 181 covers various aspects, including the testing methods for the air leakage of ducts and the requirements for nonmetallic materials used in HVAC systems.

This standard is crucial as it ensures that nonmetallic ducts can handle the pressures and conditions commonly found in ventilation systems without compromising safety or efficiency. Other standards mentioned in the choices focus on different areas, such as electrical systems or building codes, which do not directly relate to the construction of nonmetallic ducts. Therefore, UL 181 stands out as the relevant guideline for this specific application in mechanical code practices.