Why reline a chimney?

There are several possible reasons to reline a chimney:

    1. In houses built prior to the 1950s, masons often did not use terra cotta flue liners. Flue built from brick, stone, or concrete block surrounding a terra cotta flue tile liner. Chimneys that are brick, stone, or concrete block only, Flue built from brick, stone, or concrete block only, which does not contain a liner. Recognizable by the numerous gaps and mortar joints. without terra cotta flue tiles, are unsafe for use. Gaps form where mortar has fallen out and these gaps may allow excessive heat to come into contact with combustibles, or noxious flue gases to enter the home. Chimney fires can easily start house fires, and produce carbon monoxide and other deadly gases.

 

    1. When a wood stove is hooked into a thimble, Round opening where a woodstove connects to a masonry chimney. Usually made of terra cotta or metal. directly into a terra cotta lined chimney, sometimes the flue is too big for the appliance to draft properly. NFPA (the National Fire Protection Association) standards require a flue area no bigger than twice the size of the flue collar on the appliance for an exterior chimney, Chimney built on an outside wall of the house, surrounded by the outside air on three sides. or three times the size of the flue collar for an interior chimney. Chimney built in the middle of the house, surrounded by the house on all four sides. The area of a six inch flue collar (the most common) is just over 28 square inches. The area of an eight inch flue collar is just over 50 square inches. Terra cotta tiles vary a lot in their thickness, so it is a good idea to measure the interior dimensions to get an accurate read. Typically an 8X8 flue tile has an area of 49 square inches, an 8X13 flue tile has a free area of 84 square inches, and a 12X12 flue tile has an area of 121 square inches.

 

  1. Wood stoves or wood stove inserts installed in fireplaces should have a full liner stainlesslinerstainlessliner2 Chimney lined with a full stainless steel liner from the top of the stove or insert to the top of the chimney. all the way to the top of the flue. While building code allows for a direct connect, A direct connect is when an insert or a woodstove is installed into a masonry fireplace without a full liner. Instead it will have a short length of stainless liner (oven an oval or rectangular shape) extending just to the bottom of the flue (the terra cotta tiles).NFI does not allow them and Wooden Sun does not install them, for the following reasons:
    • The appliance will not draft as well because the flue is so much bigger than the flue collar.
    • The appliance will take a lot longer to start up and begin draft properly because heating up a much larger flue takes significantly longer than heating up a stainless liner wrapped in an insulation blanket.
    • Because of the drafting issues, the appliance will never be as efficient, meaning that it will take more wood to heat the same amount of space.
    • These types of installations can be dangerous and are more prone to chimney fires.
      • Direct connects produce a lot more creosote Creosote is a material that forms when woodis burned incompletely. It is flammable, and is a frequent cause of chimney fires. It has a strong odor that can be more pronounced in the summer months, when it melts in the heat. because the flue gases cool down so much more, forming glazed creosote Also called third degree creosote, this type of creosote catches fire relatively easily and burns very hot and very fast. that cannot be removed from a normal sweep (requires a rotary sweep). Third degree creosote burns very hot, very fast.
      • Unless the direct connect is completely removed (a big job requiring moving the appliance and taking apart the direct connect), the area where the direct connect goes into the flue cannot be reached to clean–a lot of creosote forms in these spaces and if it is not swept properly the creosote buildup is signficant. This can catch fire and be the beginning of a significant chimney fire.
    • Fully lined chimneys are much safer if a chimney fire were to occur. With terra cotta tiles only, it is possible for the chimney fire to spread through voids in the mortar or cracks in the flue tiles. A full liner is a chimney system within a chimney system–the fire can be contained by the stainless liner and insulation, with the added back up of the terra cotta and masonry chimney.
    • In summary, direct connects are the height of “penny wise and pound foolish.” While they are initially a cheaper installation, in just a few years the full liner will have paid for itself in increased efficiency and decreased cleaning costs, not to mention dramatically improved safety.
  2. Occasionally, because of a chimney fire, earthquake, or age, terra cotta flue tiles develop cracks Vertical cracks in a chimney flue are usually caused heat expansion and contraction, as often occurs with chimney fires. Horizontal cracks are usually caused by physical movement, such as an earthquake. that render the chimney unsafe to use without being relined, either with a stainless steel liner or a poured refractory liner.