Homeowners often get confused when they hear that their chimney needs to be relined.
The first thought that may come to mind is, “What the heck does that mean?” This writer will attempt to explain – in laymen’s terms – what relining is, why it may be needed, and all of the options available so that you can make an informed decision about your chimney repair.
Simply put, relining means installation of a new flue liner. However, the process is far from a simple undertaking and requires a professional to do the installation work.
If you have been told that your chimney needs to be relined, the reason may be that the flue liner is damaged, misaligned, missing mortar joints, it is sized incorrectly, or that there is no flue liner at all.
Flue liners have been required since 1927 by code to serve two purposes: First, to allow for the smooth passage of smoke and toxic flue gasses to exit the home without restriction, and second, to reduce the exterior temperature of the chimney during use.
Flue liner damage may, and often does, occur during a chimney fire, lightning strike, foundation movement, or piering (moving the chimney back into position and installing piers to hold it in place).
Over time, flue mortar joints exposed to rain and acidic flue gasses deteriorate and disappear altogether. Gaps in the liner due to any of these damages can be a serious hazard.
After a qualified professional chimney contractor has evaluated your particular chimney, s/he will offer one of the following methods for relining:
Vitreous Clay Tile Chimney Flue Liners
These have been used since the 1900’s and are a readily available and relatively inexpensive construction material. Tile flue chimney liners crack when there is a temperature differential of 500 degrees (as during a chimney fire), and will eventually soften and spall especially if exposed to condensation in a gas flue.
At the time of original construction, the mason installs the tiles ahead of the masonry surrounding them which allows him to make certain that the tiles are straight and the joints are smooth.
Relining with tile is difficult, if not impossible, to do except for very short sections. For this reason, very few contractors will offer this option. If the option is offered be sure to ask how they are going to do the installation, what equipment is used, and how much masonry will need to be removed from your chimney in order to access the interior.
In some cases, it is impossible to reline with tile without tearing down all or part of the chimney, and that is why most chimney technicians offer to reline with steel instead.
Stainless Steel Chimney Liner
Stainless Steel chimney flue liners are a more modern product. All stainless steel flue liners are U.L. listed or tested to U.L. 1777 Standards, which means that they have been subjected to a series of tests including three 10-minute 2100-degree burns.
Steel flue liners will withstand exposure to a chimney fire of short duration, but can become damaged in long-burning fires. Steel liners come as rigid or flexible, and in different grades i.e. 304 grade stainless, which is very heavy, or 361 Titanium/stainless steel, which is lightweight, yet sturdy. Your chimney technician will know which type is best for your particular application.
Most flexible steel liners can be custom-shaped to fit the flue as well.
Most also require the addition of insulation in the form of foil-faced ceramic wool blanket or Thermix insulation. This keeps the liner warmer and reduces heat transfer to surrounding masonry. With the proper amount of insulation a “zero clearance” installation can be achieved. This is important if combustible materials nearby do not have proper clearances.
Removal of the original tile flue liner is often necessary in order to gain the necessary room for a properly sized flue liner. Anytime a liner is inserted inside the old liner it is “downsized,” or smaller than the old liner.
The interior dimensions of the flue liner are critical to the operation of a fireplace or wood or gas appliance, and if too small or too large will not draft or function properly.
The International Residential Code indicates specific liner sizes which must be adhered to.
Unfortunately, not all chimney technicians have the equipment needed to remove tile flue liners, so it is important to check the liner size before it is installed.
The typical flue liner serving an open wood-burning fireplace should be 1/10th the size of the fireplace opening dimensions. In most cases, stainless steel will be the first, or only option offered due to its popularity.
Cast-in-Place or Ceramic Chimney Flue Liners
Cast-in-Place or Ceramic Chimney Flue Liners are the best, and consequently the most expensive liners available today. Cast liners are listed or tested to U.L. 1777 Standards and for zero-clearance applications.
The benefits of this type of liner are that it can be sized exactly to the appliance it will be serving, can be used for multiple-flues in the same chimney, and actually strengthens the chimney.
Cast liners are installed by using a heavy rubber tube which is inflated inside the chimney. A mix is poured around the tube and left to cure overnight. While the mix is poured it seeps into holes or cracks in the chimney which strengthens the structure. The next day, the tube is deflated and removed, leaving a hard, ceramic flue liner.
No matter what type of flue liner you decide to use, if you do not feel comfortable with the liner option offered by your chimney technician, get a second opinion.
Be sure to do your research on the company you take advice from and check their website for information on their years in business, methods of relining offered, and their training, certifications, and licensing.
For more details on each type of flue liner see my other articles on chimneys.com.