Every duct or pipe shall be constructed of galvanized metal sheets in accordance with the provisions of Table 57.2404.7.9.1.
Duct Cross-Sectional Dimension in Inches | Gauge of Duct Metal |
Up to 8 | 24 |
Over 8 inches to 18 | 22 |
Over 18 inches to 30 | 20 |
Over 30 | 18 |