Why Do I Need a Chimney Liner?


Improper chimney sizing is primarily an issue when venting appliances. A very common example of this is the fireplace insert or woodstove which is vented without a proper liner into the smoke chamber of a typical fireplace. This is a real problem. This type of installation is commonly referred to as a slammer. Slammers are notorious for creating dangerous messes of creosote which can ignite into a chimney fire. Chimney fires are very dangerous things. In addition to pass through heat which can ignite the combustibles surrounding or adjacent to a masonry chimney, burning debris can exit the chimney and ignite a home from the roof down.

The way to eliminate the problems created by a slammer type installation is to properly vent all appliances with a liner sized to each appliance. One may also want to consider updating any woodstove or fireplace insert which was not produced in the last 15 years. During that time incredible strides has been made in woodstove design making available woodstoves which when installed properly, burned properly, and cleaned annually are much cleaner and safer than those which produced larger amounts of creosote in the past.


Missing, Damaged, or Poorly Installed Flue Tiles:

As required by the national standard for masonry fireplace construction (NFPA 211), all masonry chimneys must have at least a flue tile in good condition installed within the masonry structure to exhaust combustion gases of the fireplace or appliances attached to them. If those flue tiles are improperly installed (misalignment is the most common problem), cracked from sudden thermal expansion, or missing due to poor chimney design the chimney is sub-standard and potentially dangerous.

In the case of a traditional wood fireplace or woodstove, creosote is able to pass though cracks or openings in the flue tiles and be absorbed into the porous masonry structure of the chimney. If this occurs, a chimney fire will not be contained inside the flue tile vent system with dangerous results a real possibility. In addition to possible creosote problems, cracked, missing, or poorly installed flue tiles can allow exhaust gases to seep though crack in the brick structure of the chimney into a home. This situation has the potential to lead to a carbon monoxide poisoning situation.


Condensation Issues:

All natural draft chimney function due to temperature differences between the outside of the home and the exhaust gases. The draft created by this temperature difference draws the exhaust gases produced by a fireplace or appliance safely out of the chimney. Most all fuels have as a by product of combustion elements which can condense when they come into contact with cooler surfaces. In the case or wood fired appliances and fireplaces, creosote is the condensing by-product. As shown in the picture to the right, creosote condensation can be substantial when conditions are right for condensation to occur. Creosote is the fuel for chimney fires.

The best way to ensure a chimney fire will not occur is to not have the fuel for it in the first place. In the case of natural gas or propane fired appliances the primary condensate is water. This condensation can speed up water damage to a chimney via the freeze / thaw cycle. Permanent damage to a chimney can be caused by the cracks in the structure of the chimney leading to structural failure or exhaust gases seeping into living space. The key to a condensation problem relates both to proper sizing of a vent system and its proper design and construction. This condition is a cool or cold flue. A cold flue which does not heat up properly is a surface ready to hold condensation.