Cylindrical metal chimney liners are available in rigid and flexible forms. Rigid liners are assembled from sections of pipe and lowered into the chimney. Flexible liners are made from continuous lengths of corrugated pipe that are installed inside the chimney. Differences between flexible and rigid chimney liners include cost, ease of installation, and the situations in which each is appropriate for use.
A metal chimney liner can be installed inside a clay tile chimney liner, or inside an unlined chimney, to seal the flue and prevent dangerous gases from leaking back into the building. A clay tile liner will deteriorate over time due to weathering, corrosive condensation from combustion products, and foundation settlement. A tile veneer can be repaired or replaced, but this requires expensive masonry work. Installing a metal siding is often a better budget option.
The type of metal liner that is appropriate depends on the physical configuration of the chimney and the type of application from which the liner will vent gases. The metal siding will extend from the top of the chimney to the vent of a fireplace, wood stove, furnace, or other fuel-burning appliance. If the flue is straight from top to bottom, a rigid chimney liner may be the best option. If the flue is offset or has one or more bends between the top and bottom, then a flexible liner would work better.
Materials for a rigid liner are less expensive than materials for a flexible liner, but you should factor in labor costs when calculating the cost of your fireplace liner. For a short, straight chimney that won’t require a lot of complicated joining work, a rigid liner would be the most economical. However, an offset chimney would require expert plumbing and many specialized parts to build a rigid liner that is properly sealed and safe to operate. The labor costs involved in installing a one-piece flexible liner on a crooked chimney will be much less than the cost of a rigid liner.
Future maintenance costs are another consideration when choosing between a rigid and flexible lining. Since rigid liners are assembled from shorter joints of material, they have more places to develop future leaks than a one-piece flexible liner. Rigid liners have smooth interior surfaces, so they do not accumulate creosote as easily as the corrugated interior of a flexible liner. Some manufacturers offer smooth-walled, flexible siding material at a slightly higher cost.
Some chimney specialists believe that the expansion and contraction of the corrugated metal in a flexible liner actually prevents creosote from building up by breaking it up and loosening it from the grooves as it builds up. In any case, a soft fold liner is easier to clean than a rigid liner if the rigid liner has one or more sharp angles between the top and bottom.
If you’re confused about the best type of liner to install on your chimney, your local chimney cleaning professional can provide advice during your annual chimney cleaning.
