Gypsum boards forming air ducts are restricted to which type of systems?

Gypsum boards are commonly used in the construction of air ducts, primarily because they are relatively lightweight, easy to work with, and provide good acoustic properties. However, there are specific guidelines and restrictions when it comes to their application in different types of air systems.

In this case, gypsum boards are allowed for use in return air systems, but with a critical limitation on the maximum air temperature, which is set at 125 degrees Fahrenheit. This restriction is in place because higher temperatures could compromise the structural integrity of the gypsum board, leading to potential failure of the ductwork.

Return air systems typically handle air that has already circulated through a space and is being drawn back to the HVAC unit for reconditioning before being supplied again. The air in these systems may experience variations in temperature, but it generally does not reach extremely high levels, thus making gypsum a suitable material as long as the temperature remains within the defined limits.

Other types of systems like supply air, exhaust air, or mixed air systems may encounter conditions (such as higher temperatures or more aggressive environmental factors) where gypsum boards are not deemed suitable or may not meet code requirements for safety and performance. Consequently, the application of gypsum for air ducts is particularly tailored to return air systems within the specified