What material is not to be used to vent low heat appliances?

• A. Steel
• B. Aluminum
• C. Copper
• D. Masonry

Answer: (D)

Vent systems for low-heat appliances must use materials that are listed and rated for exhaust of those appliances, giving a sealed, cleanable, and heat-tolerant path for the flue gases. Masonry isn’t used for venting low-heat appliances because it’s not a factory-built, listed vent connector; its joints are mortar-based and can crack, loosen, or leak over time, and it’s difficult to inspect and clean. Metal vent pipes—like steel, aluminum, or copper—are manufactured with proper fittings and clearances, tested for venting temperature ranges, and designed to maintain a tight seal, making them the appropriate choice for low-heat exhaust. Masonry may still be appropriate as a chimney for solid-fuel or high-heat applications with a proper liner, but not as a direct vent path for low-heat appliances.