What is the minimum nominal thickness of the metal wall for a 16"x24" galvanized duct?

The correct answer is based on the standards set for the construction of HVAC ductwork, particularly the thickness of galvanized sheet metal used in duct fabrication. For a rectangular duct of size 16"x24", the minimum nominal thickness needed for proper structural integrity and to comply with industry standards is specified.

In this case, a thickness of 0.04 inches, corresponding to No. 20 gauge, is sufficient to handle the typical pressures and operations expected in this size of ductwork. The gauge system provides a way to categorize metal thickness, and using No. 20 gauge ensures that the duct is robust enough to prevent issues like warping or fatigue due to airflow.

Other thicknesses available such as 0.05 inches (No. 19 gauge), 0.03 inches (No. 21 gauge), and 0.06 inches (No. 18 gauge) would not be the minimum requirement. While thicker materials can provide additional strength, they are not necessary for normal operating conditions of a 16"x24" galvanized duct, which is why No. 20 gauge is identified as the most appropriate choice for this application.