What is the maximum sheet length for lining as specified in the guidelines?

The maximum sheet length for lining, as specified in the guidelines, is important for ensuring the proper installation and performance of HVAC systems. A length of 10 feet allows for a balance between manageable size for transportation and handling during installation while providing sufficient coverage to minimize joints and seams. This length enhances the structural integrity of the ductwork and reduces the potential for leaks. Utilizing sheets longer than this specification could lead to practical issues in handling and installation, as well as increased risk of damage or inaccuracies in fitting.

In the context of the given choices, while other lengths may be mentioned, the guidelines clearly define 10 feet as the optimal maximum for installation purposes, ensuring reliability and efficiency in the HVAC system's operation.