What Is the Difference Between Asbestos Vs. Fire Brick in an Old Boiler?


Chimneys provide an essential means to eliminate toxic fumes generated by any heating system, including boilers. Chimneys for a lot of homes used to be made with asbestos and fire brick materials. Many of those older homes with the original chimneys may have problems when these materials deteriorate. Asbestos and fire brick differ in the types of safety and health risks created when they break down.

Boiler Facts

  • Old boiler systems were a popular form of home heating in the early 20th century. While contemporary boiler systems use water to transport heat, older systems transferred heat through steam. Much like hot water boilers, steam boilers use fossil fuel sources such as gas, oil or coal to produce steam. Homes built during the early 20th century may still use steam boilers for a heating system. Any type of boiler unit requires a chimney flue to expel exhaust gases. Asbestos and fire brick were just some of the materials used to construct older chimney structures.

Chimney Flue Surfaces

  • Chimney flue surfaces are a channel to remove the potentially toxic gases produced by burning fossil fuel from the boiler. Over time, the heat and gas wears away at the chimney flue surface. According to the website Old House Journal, clay tile chimney liners became common practice in the early 1900s. The liners provide an extra layer of protection within the chimney flue. Asbestos and fire brick suffer equally from combustion exhaust without liners.

Fire Brick

  • Many older chimney designs used fire brick as a primary building material. Some chimney structures may have a single line of bricks as the actual chimney wall. The single line of bricks method, also known as single wythe flues, creates chimney walls with a 4-inch thickness. Few older chimneys were constructed with protective chimney liners, so this single layer of fire brick is prone to deteriorate. Fire brick deterioration can lead to gaps and cracks inside a chimney wall. Combustion gases may seep into the home through those openings. Wall deterioration can also pose a fire hazard if sparks enter the home's interior walls.


  • Some older chimney structures were made with asbestos cement, or transite. Transite was used as a mortar material between the years of 1905 and 1950, according to Asbestos.com. Asbestos cement was typically used to build chimney flue walls. Asbestos may also appear in certain adhesives and joint compounds used to make chimney structures. Asbestos cement and adhesives were used because they have high heat-resistance properties. However, the mortar materials do break down. When that happens, asbestos fibers can become airborne in the home. Regular exposure to asbestos can cause significant damage to a person's respiratory system.

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