What venting material is required for Category III appliances?

The correct choice for venting material required for Category III appliances is stainless steel. Category III appliances are designed to operate with positive vent pressure and are classified for venting systems that handle products of combustion that are not condensing.

Stainless steel is favored for these applications because it is highly resistant to corrosion, especially in the presence of high temperatures and potentially acidic byproducts of combustion. This durability helps maintain the integrity of the venting system over time, ensuring safe and efficient operation of the appliance. Additionally, stainless steel can endure the pressure conditions associated with these appliances without the risk of failure, which is critical for preventing hazardous situations that could arise from venting failures.

Other materials such as aluminum, galvanized steel, and plastic do not meet the necessary requirements for the same level of durability and resistance when handling the specific conditions seen in Category III installations. Hence, stainless steel is the recommended and required material for venting in such cases.