Which type of duct is not typically embedded in concrete?

The type of duct that is not typically embedded in concrete is paper-fiber duct. Paper-fiber ducts are generally used in low-pressure heating and cooling systems and are favored for their lightweight and ease of installation. However, they are not designed to withstand the moisture and potential degradation that can occur when embedded in concrete, which can compromise their performance and lead to structural issues over time.

On the other hand, other duct types such as steel, galvanized-coated, and aluminum-coated ducts are made from materials that are much more durable and resistant to the harsh conditions associated with concrete environments. These materials can withstand the compressive forces and moisture levels present in concrete without suffering damage, allowing them to be embedded safely during construction. This distinction is important for contractors to understand to ensure proper installation and long-term functionality of duct systems within concrete structures.