What is the required thickness for sheet steel used in duct construction according to the Mechanical Code?

The required thickness for sheet steel used in duct construction is determined based on the intended application and the size of the ducts. Generally, No. 26 gauge sheet steel is often specified for smaller ducts or less demanding applications because it provides a balance between strength, weight, and cost.

For various duct sizes, particularly for ducts that are designed to handle moderate air pressure and flow, No. 26 gauge offers sufficient structural integrity while still being lightweight enough for ease of installation. This gauge meets the standards set forth in the Mechanical Code for residential and light commercial applications, ensuring that the ducts can withstand normal operating pressures without excessive deformation or failure.

Conversely, other gauges like No. 18, No. 20, and No. 22 tend to be thicker and may be specified for more demanding applications requiring greater strength or for larger duct sizes where more rigidity is required to resist pressure changes. However, for the common scenarios outlined in the code, No. 26 gauge is typically adequate and thus makes it the correct answer.