Sheet Metal Journeyman Practice Test

Gypsum ducts are interior ductwork made from gypsum board and are used primarily for return air, not for hot supply air. They are limited to a maximum operating temperature of 125°F because the gypsum core, paper facing, and the joining materials aren’t rated for higher temperatures. Exceeding 125°F can weaken the duct, cause sagging or delamination, and reduce fire-rated performance. So 125°F is the correct maximum. Values above that (150°F, 175°F) would exceed the material’s rating, while 100°F is below the limit but not the maximum allowed.