Which material is not suitable for venting low-heat appliances?

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

Answer: (D)

When venting low-heat appliances, the vent path needs to be a sealed, predictable, and corrosion-resistant conduit made from listed venting materials. Copper, steel, and aluminum fit that requirement because they can be formed into tight, continuous runs with properly sealed joints that safely carry the exhaust out of the building.

Masonry, while noncombustible, is not suitable as the main vent material for these appliances because it is porous and difficult to seal and inspect. Without an approved liner, moisture, condensation, and flue gases can deteriorate joints and seep leaks, making the vent path unreliable. If a masonry chimney is used, it must be lined with an approved vent liner to provide a proper, safe vent path; otherwise it’s not appropriate for venting low-heat appliance exhaust.