A chimney liner is, in fact, a lining that goes in the flue of the chimney. The flue is a tunnel or passageway located within the chimney structure.  A flue lining is made of clay, ceramic, or metal conduit and is intended to contain the burning products, and direct them to the outside atmosphere while protecting the chimney walls from heat and corrosion (similar to an exhaust for a car).

FAQs About Chimney Liners

Do you really need a chimney liner?

Chimney liners create a clear and direct path for smoke to exit your home safely and efficiently. Without one, the chimney walls will eventually deteriorate, and smoke will be able to seep through any cracks. When your chimney cannot effectively release smoke outside, it greatly increases the risk of a chimney fire. The chimney liner is one of many chimney components that keeps your chimney working safely and smoothly.

How would I know if my chimney needs a new liner?

Unlined Flue

In the 1920s chimneys began to be built with clay tile liners. Most chimneys we encounter before this period are unlined and consist of just brick and mortar. This is not only concerning for carbon monoxide transmission, but also for heat transfer to neighboring construction materials. If your chimney is unlined, it should be lined for use.

Clay tile lined flue

Most chimneys built in this area after the 1920s are clay tile lined. Clay tiles are usually square or rectangular and in two-foot lengths. These sections are mortared together within the flue walls to create a barrier to the exposed brick and mortar. Over time, these sections, as well as the mortar between them, break down. This is mainly due to soot accumulation (high acid content) or moisture. Moisture can penetrate the brick (porous), come in from above (the flue opening) or from within with poor wood or gas fueled appliances. When there is a break or breach in the lining, the flue should be lined for use.

What are Chimney Liner Benefits?

The most significant benefit of having a chimney liner is that it increases your home and family’s safety. When you use your heat, exhaust and carbon monoxide gets released so ensuring that the by-products of combustion are removed at all costs. Similarly, heat and smoke from your fireplace can enter the home during an improperly venting fire. This increases the residence time the smoke spends within the walls and creates soot buildup. Excess soot buildup is flammable and is how a chimney fire is formed.

There are various types of chimney liners on the market and most depend on how you are going to use your fireplace or heating flue. Whether you go from gas to wood burning or vice versa, you must install a new chimney liner appropriate for that type of fuel and use. The same rule applies to heating and hot water equipment because different materials are more suited for different types of fuel.

What Kind of Liner Do I Need?

Well, that’s depends…. What are you venting?

Different applications call for different types of liners. Fireplace liners are larger diameter stainless steel, heating flue liners can be 316 alloy stainless, AL29-4C alloy stainless or aluminum. All these vary significantly in price.

Heating Flues / Oil + Gas:

Liners have maximum BTU ratings which are primarily calculated based on height and diameter. The BTUs from all appliances are added together and cross referenced in the NFPA 54 (National Fuel gas Code). This will give you the required diameter for the existing appliances.

High Efficiency Heating:

Most gas high efficiency boilers require a 3″ or 4″ AL29-4C alloy stainless steel vent, when chimney vented. These lining systems have a slightly different type of installation with elbows instead of tees and rigid extensions at the peak. The boiler manufacturer sets the diameter regulations. These boilers cannot be common vented or installed in a flue with other appliances venting around it. High efficiency boilers do require fresh air and may be able to be pulled from the chimney with an aluminum duct.

Fireplaces / Gas Logs:

Fireplace flues are sized based on a ratio of the net cross sectional area of the fireplace opening. When you are unable to attain that ratio, additional work may be needed to achieve optimal draft. And don’t neglect the smoke chamber! Usually the smoke chamber will need to be sealed as part of the relining process.

Gas Inserts:

Gas inserts require two smaller liners, one for exhaust and one for fresh air. Both liners are installed into one flue and can usually be aluminum.

Aluminum – An aluminum liner can be used to vent category 1 gas appliances with A.F.U.E. of 83% or lower. Aluminum liners are commonly used to downsize and vent orphaned water heaters when the main heating system is vented elsewhere, improving the performance of the appliance.

Stainless Steel 316 alloy (most common)– Stainless steel liners are designed to reline existing chimneys or be used in new construction. It’s corrugated construction allows for expansion and contraction during the heat up and cool down periods. This liner would be used for standard heating flues and fireplace flue installations.

Stainless Steel /AL29-4C – AL294-C alloy can only be used with natural gas or propane category II, III or IV appliances. Frequently used to chimney vent modern high efficiency boilers.

Polypropylene/PVC – Plastic venting may be an option to vent approved condensing boilers. Manufacturer’s specifications would determine if plastic venting is right for you.

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