Which material is not approved as a flue lining system for low heat appliances?

Which material is not approved as a flue lining system for low heat appliances?

• A. Clay tile
• B. Stainless steel
• C. Concrete block
• D. Masonry block

Answer: (D)

Flue liners must be noncombustible, rated for the heat they’ll experience, and designed to provide a smooth interior surface to minimize creosote buildup and allow safe venting. Clay tile is a classic, purpose-built lining material for chimneys, and stainless steel liners are widely used for their durability and ease of retrofit. Concrete block can be acceptable in some lining scenarios because it is a masonry material that can be installed with proper clearances and supports, and it can be used in certain chimney designs. Masonry block, however, is not a proper, listed flue lining material because it isn’t manufactured or tested as a dedicated liner, it’s porous and can have irregularities and joints that trap moisture or creosote, and it may not withstand the thermal and chemical conditions inside a flue. For these reasons, masonry block is not approved as a flue lining for low-heat appliances.

Flue liners must be noncombustible, rated for the heat they’ll experience, and designed to provide a smooth interior surface to minimize creosote buildup and allow safe venting. Clay tile is a classic, purpose-built lining material for chimneys, and stainless steel liners are widely used for their durability and ease of retrofit. Concrete block can be acceptable in some lining scenarios because it is a masonry material that can be installed with proper clearances and supports, and it can be used in certain chimney designs. Masonry block, however, is not a proper, listed flue lining material because it isn’t manufactured or tested as a dedicated liner, it’s porous and can have irregularities and joints that trap moisture or creosote, and it may not withstand the thermal and chemical conditions inside a flue. For these reasons, masonry block is not approved as a flue lining for low-heat appliances.