Which material is approved for use as combustion air ducts?

Galvanized steel is an approved material for use as combustion air ducts due to its durability, resistance to corrosion, and ability to withstand high temperatures associated with combustion processes. This material ensures that the ducts maintain structural integrity and performance over time when exposed to the conditions of a combustion environment.

Additionally, galvanized steel is widely used in HVAC applications because it can be manufactured to fit necessary standards for airflow and pressure, making it effective for directing combustion air into heating appliances. The use of materials like aluminum, PVC, or fiberglass might not meet the same safety and performance standards required for combustion air ducts, especially in terms of fire resistance and structural reliability in extreme conditions.