Chimney liners overview

EXCEL Chimney from ICC Industrial Chimney

Some homeowners have asked Chimneys.com to provide some basic information about their chimney liner.  With all the different types of chimney liners, the strength and weakness of each and their different applications, one can understand the need for clarification.  This article will attempt to provide answers.

The primary purpose of a chimney liner is to contain the products of combustion within your chimney.  These products of combustion can be in the form of liquids, solids, gases and heat.

When combustion occurs, high temperature gases are vented into your chimney.  These hot gases can transfer their heat through the chimney to the combustible areas of your home and cause a structure fire if the chimney liner were not able to contain this heat. 

Some heating appliances vent gases in excess of 1000° F/537° C.!!

When liquid creosote found in wood smoke condenses into a solid fuel in your chimney, the potential for a chimney fire exists and this can produce temperatures in excess of 2000° F/1093°C. 

Chimney inspections often reveal the original construction of the chimney does not meet standard building codes.  Sometimes the chimney is in direct contact with the wood structure of the home.  In this case even an undamaged chimney liner may not be sufficient to contain the heat produced within your chimney. 

Chimney lining systems that are insulated and U.L. Laboratory Tested for Zero Clearance to Combustibles may provide a degree of increased safety when installed according to the manufacturer’s instructions.

The gases formed in combustion also contain carbon monoxide.  This odorless gas must be completely contained within the lining system to prevent deadly carbon monoxide poisoning. 

Inspection often reveals deteriorated lining systems from the high efficiency appliances used today that produce large volumes of water vapor within the lining. Many of these liners are no longer able to contain gases. 

Homeowners need to be aware of the need for annual inspections of their chimney systems and in particular flue systems venting gas and oil furnaces to insure the linings remains sound.

The inside of a cast chimney linerThe size of the lining system can greatly affect the efficiency of the heating appliance.  Many chimney liners are too large for the application of the stove or even a new furnace.  Installation of a smaller, properly sized, lining system may be the best approach to upgrading.

The opposite is true for many fireplace flue liners.  When the original construction was completed, the lining may not have been sufficient to handle the volume of air flow needed to vent the current size opening of the fireplace.  Often the choice is to install a larger lining system or reduce the opening of the fireplace to provide the air flow needed to prevent smoke spillage.

Masonry chimneys usually have a square or rectangular shaped tile lining system.  This shape is more convenient for construction but less efficient for air flow.  Smoke travels in an elliptical twist while traveling up the flue system.  For this reason round linings are much preferred.

The tile lining is made from terracotta which is an excellent insulator and low in material cost.  The problem with tile linings is they are such a great insulator the inner surface may be several hundred degrees hotter than the outside surface.  At some point this differential of temperature between the inner and outer surface of the tile results in the tile twisting and cracking.  Once a tile liner is cracked, it no longer can contain the products of combustion and must be replaced.

If the broken tiles are simply near the top of the chimney and may have cracked from freeze thaw cycles, just the top tiles can be replaced.  However if the tiles are damaged all the way down the flue system, the chimney must be relined. 

Relining with tile is not an option because to do that the chimney would have to be torn down.  Replacement lining systems made of high temperature alloy stainless steel or a cast in place masonry system can be used to reline without having to tear the chimney down.

The choice of the type of chimney lining system needed to reline the chimney has several variables in both price and the future use of the chimney. A complete discussion of the benefits in choosing the different types of relining materials shall be addressed in a follow up article.

Your chimney lining requirements may change over the years depending on upgrades to your heating system, the after effects of a chimney fire and the desire you may have to return to using your open fireplace. 

Contact one of the chimney sweeps on this site for expert recommendations and above all, do your homework before choosing the chimney repairs you may need.

Homeowners today have many new options to upgrade their chimneys. Chimney experts today have many new products available to insure your repairs are long term solutions. Planning your chimney project for the spring can result in getting better service at a lower cost compared to having the work performed in the fall or during the heating season.  Watch for upcoming articles on Chimneys.com for more information about chimney lining.

~ Dave Hannah

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