Flexible vs rigid chimney liner?

Lining a chimney makes a flue safe and efficient for a modern appliance, but the two liner types suit different situations. The flue's shape usually settles the decision before anything else.

What a flexible liner is

A flexible flue liner is a continuous corrugated stainless-steel tube supplied in a coil, which can be fed down the chimney from the top in a single length. Its great advantage is that it can bend and twist to follow an offset or non-straight flue, which is exactly what many older British chimneys are — they rarely run dead straight from the fireplace to the pot. This makes flexible liner the standard choice for retrofitting a wood-burning or multi-fuel stove or relining an existing open-fire flue, because it can negotiate the bends without the chimney being opened up.

Flexible liner comes in different grades of stainless steel suited to different fuels and usage — a higher grade is specified for more aggressive conditions and continuous use, a standard grade for intermittent burning. It is quicker and less disruptive to install than rigid liner in an existing chimney, and it is the workhorse of stove installations. Its trade-off is durability: because it is a thinner, corrugated material, a flexible liner generally has a shorter expected life than rigid, and the cheaper grades less still, so matching the grade to the fuel and use is important to get a reasonable lifespan.

What a rigid liner is

A rigid liner is built from straight, jointed sections of stainless steel (or, in some systems, other materials) assembled to form the flue. It is thicker, stronger and longer-lasting than flexible liner, and because it is straight-section it offers a smooth internal bore with good flow. Rigid liner suits a straight flue, a new chimney or new build, and situations where maximum durability and the longest service life are wanted.

The limitation is geometry. Because it is made of straight pieces, a rigid liner cannot easily follow the bends and offsets of a typical old chimney, so it is awkward or impossible to install in a flue that is not reasonably straight without significant work. Installation is generally more involved and more costly than dropping in a flexible liner, and it is often a new-build or major-works choice rather than a quick retrofit. Where it does suit the flue, though, the payback is a more robust liner that should last considerably longer before it needs replacing.

Comparing the two

The table summarises the practical differences. The right liner depends on the flue's shape, the appliance and how long you want it to last; the figures are indicative only.

Indicative figures for guidance; flue length, access and grade drive cost. Sources: HETAS / Checkatrade guidance.

Choosing the right liner

For most homeowners the decision is made by the flue and the appliance. If you are fitting a stove or relining an existing open-fire flue, and the chimney bends or offsets as old ones usually do, a flexible liner of the correct grade for your fuel is almost always the practical answer. If you have a straight flue, a new chimney, or are building new and want the longest-lasting result, a rigid liner may be worth the extra cost and work. Whichever type, the liner must be compatible with the appliance and fuel and installed correctly — the right diameter, the right grade, properly sealed and supported. Because a flue serves a combustion appliance, getting this wrong has safety consequences, so lining work for solid fuel should be carried out by a HETAS-registered installer (or appropriate competent person), and for gas by a Gas Safe registered engineer. They will assess the flue, confirm whether it bends, and specify the correct liner type and grade.

Frequently asked questions

Sources & further reading

• HETAS — flue lining and solid fuel guidance
• Checkatrade — chimney lining costs
• HomeOwners Alliance — chimney guidance

Figures on this page are typical UK ranges drawn from published sources and depend on your specific chimney. They are guidance, not a quotation.