What type of flexible duct is limited in length according to the standards discussed?

Flexible air connectors are specifically designed to connect various HVAC components while allowing for some movement and adjustments. The standards stipulate limitations on their length to ensure that they function effectively without compromising the airflow efficiency or leading to increased system resistance. When these connectors exceed a certain length, the likelihood of sagging, kinking, or other forms of obstruction increases, which can negatively impact the performance of the HVAC system.

Metal ducts, rigid ducting, and insulated flexible ducts, while they may also have certain specifications and guidelines, do not have the same length limitations as flexible air connectors. Metal ducts and rigid ducting are typically more stable and can be installed in longer runs without similar issues affecting airflow. Insulated flexible ducts, while designed for specific insulation standards, are not limited in length in the same manner as flexible air connectors, as long as they are installed according to the manufacturer's instructions and code requirements. Thus, the focus on length limitations for flexible air connectors is crucial for maintaining the effectiveness and efficiency of HVAC systems.