Chimney Flue Liners

Simply put the NFPA 211 Standard defines a flue as: NFPA 211 3.3.73 Flue. The general term for a passage through which gases are conveyed from the combustion chamber to the outer air. The essential function of a chimney is to safely convey flue gases through the flue to outside of your home. Flue gases may be from a gas fired furnace an oil heater or a wood burning stove among others. Not only can flue gases be extremely hot, flue gases can contain hazardous compounds like carbon monoxide, sulfur, water vapor, creosote and the cancer causing carcinogens found in wood smoke. Cracked, broken, deteriorated or otherwise leaky flues can allow flue gas infiltration into the home. They can also allow heat to escape and come into contact with combustible materials in the walls of the home causing a structure fire.

Chimney Relining

The NFPA 211 says “Where masonry chimneys are relined, the liner shall be listed or of approved material that resists corrosion, softening, or cracking from flue gases at temperatures appropriate to the class of chimney service.”

This is why I recommend UL 1777 listed liner systems or HeatShield Cerfractory Flue Sealant where applicable.

Types of Flue Liners

The most common types of flue liners and basic information regarding each are listed below.

Pumice Flue Liners

There are many chimneys in Coeur d’Alene and Spokane lined with pumice liners. (Flue liners are also called flue tiles). These usually pinkish colored liners were readily available and inexpensive. These liners are no longer available and not to current codes and standards. These flue liners are porous allowing moisture and creosote to penetrate the lining making it impossible to clean out and softening the liner over time. When these flue tiles fail many times they are nearly impossible to break out of the chimney to make room for a new liner installation.

Clay Flue Liners

Vitrified clay flue liners must comply with the ASTM C315 Standard Specification. Clay flue liners must be made from fire clay, shale, surface clay, or a combination of these materials. When formed and fired (vitrified) the product must be¬†“strong, durable, serviceable”. Clay flue liners must be heated gradually or they can crack. If the liners are heated quickly the inside can expand more rapidly than the outside resulting in stress. If this differential heating is great enough the liner will crack.

Stainless Steel Liners

More to come…


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