How is duct liner attached to the metal if the duct measures 20 x 16?

Duct liner is typically attached to metal ductwork using a combination of pins and glue to ensure a secure and effective installation. The use of pins helps to hold the liner in place during the curing process of the adhesive while also providing long-term support. Glue alone may not provide enough mechanical retention, especially in larger ducts like a 20 x 16 layout, where there are more substantial forces at play due to airflow and temperature changes.

Using just pins might not offer the same level of adhesion and can lead to detachment over time, especially if the pins are not evenly spaced or if there are vibrations in the system. On the other hand, Z bars are more typically used in joints or to secure liners in areas where extra support is needed rather than as the primary method for attaching duct liner.

Therefore, the combination of pins and glue is the most effective method for securing duct liner to metal ductwork, providing both an initial hold and continuous adhesion.