In the construction of ducts penetrating a wall or ceiling to a garage, which material is approved?

The correct choice indicates that a minimum of No. 26 gauge steel is approved for ducts penetrating a wall or ceiling to a garage. This is significant because the gauge of the steel relates to its thickness and strength, which are essential for ensuring that the ductwork can withstand potential fire conditions and mechanical stresses that could occur in such areas.

Using a minimum of No. 26 gauge steel helps ensure that the ducts maintain their structural integrity and reduce the risk of fire spreading between the garage and living spaces. This gauge provides a balance between durability and weight, making it suitable for such applications.

In regard to the other options, while there are heavier gauges that could theoretically be used, the No. 26 gauge specification meets safety and building code requirements most effectively for this particular scenario. Utilizing either a thicker gauge (like No. 24) may not be necessary or economical, while thinner gauges (like No. 22 or lighter) would not provide the same level of fire resistance and structural characteristics required.