Block Chimney Vs. Class A Chimney

Block Chimney

• Block chimneys are made of concrete and are formally referred to and categorized as masonry chimneys. Block chimneys are typically built by mason workers, or in some cases the homeowner, and found in older homes, particularly those that have an all-brick or stone fireplace. Many older block chimneys were built prior to changes in building codes and owners find them in need of repair, or total replacement.

Class A Chimney

• Class A chimneys are made from high-quality stainless steel. All Class A chimneys must bear the UL (Underwriter's Laboratory) seal of approval. Class A chimneys are used for a variety of purposes, including fireplaces and wood-burning stoves. Most newly constructed homes, or those that add on a fireplace or wood stove use Class A chimneys. Class A chimneys can be installed to run up the side of your home or straight through the interior of the home and through the roof. They include an interior stainless steel liner for additional insulation and fire protection.

Block Chimney Safety Considerations

• Many home fires take place because of improperly functioning block chimneys. Another big issue with block chimneys, in particular, is the potential for water damage and deterioration. Their exposure to water can cause the mortar to loosen and the blocks to become dislodged. Older block chimneys need to meet National Fire Protection Agencies 2011 standards for safety. Make sure that the chimney has a height that is at least three feet taller than the point where the chimney touches the roof line. Another important standard is to make sure that the flue for the chimney does not vary in size within six inches below combustible materials that the chimney has to pass through, such as flooring, ceiling or roofing materials. If the blocks themselves are less than four inches thick, the chimney will not meet the national requirements for safety.

Class A Safety Considerations

• Class A chimneys do not get a "pass" on an annual inspection. Even though they are more durable than block chimneys, they have safety issues of their own. Do an annual inspection of the rain collar and flashing, the support box and the interior insulation. The rain collar and flashing keep your chimney from leaking water inside your home. The support box is located on the roof or exterior side walls of your home (whichever your chimney makes contact with when it vents outdoors). You want to make sure that the support box is firmly anchored to the roof or walls of the house. Also, check the interior insulation for signs of wear and tear or rust.