The Difference Between Flexible and Rigid Chimney Liners

Cylindrical metal chimney liners are available in rigid and flexible forms. Rigid liners are assembled from sections of pipe and lowered inside the flue. Flexible liners are made of continuous lengths of corrugated tubing which are installed inside the flue. Differences between flexible and rigid chimney liners include cost, ease of installation and situations where 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 settling. A tile liner can be repaired or replaced, but this requires expensive masonry work. Installing a metal liner is often a better economic choice.

The type of metal liner that is appropriate depends on the physical configuration of the chimney and the type of application the liner will be venting gases from. The metal liner will be extended from the top of the chimney all the way to the vent of the fireplace, woodstove, furnace or other fuel burning appliance. If the flue is straight from top to bottom, a rigid chimney liner may be the best choice. If the flue is offset, or has one or more bends between top and bottom, then a flexible liner would work best.

The materials for a rigid liner are less expensive than the materials for a flexible liner, but you have to take labor costs into account when you are estimating the cost of your chimney liner. For a short, straight flue that will not require a lot of complicated joint work, a rigid liner would be the cheapest. But, a flue with offsets would require skilled pipe fitting and a lot of specialized parts to build a rigid liner that is properly sealed and safe to operate. The labor costs involved in installing a single piece flexible liner in a crooked flue will be far cheaper than the cost of a rigid liner.

Future maintenance costs are another consideration in choosing between a rigid and flexible liner. Since rigid liners are assembled from shorter joints of material, they have more places to develop future leaks than a single piece flexible liner does. 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 liner material at a little higher cost.

Some chimney specialists believe that the expansion and contraction of the corrugated metal in a flexible liner actually keeps creosote from building up by cracking it and breaking it loose from the grooves as it accumulates. In either case, a flexible liner with smooth bends is easier to clean than a rigid liner if the rigid liner has one or more sharp angles between top and bottom.

If you are confused about the best type of liner to install in your chimney, your local chimney cleaning professional can give you advice during your annual chimney cleaning.