The short answer
A chimney liner is a sound inner passage inside the flue that carries combustion gases safely out of the building. It can be a flexible stainless-steel liner dropped down the chimney, a rigid (pumice or clay) liner built in, or a cast in-situ lining. You may need one if the existing flue is cracked, leaking, oversized or deteriorated, if combustion gases or tar staining are getting through the brickwork, or when fitting a stove into an old chimney that needs to match the appliance's flue. Relining is controlled work under Approved Document J, so it must be done by a HETAS-registered installer who self-certifies it, or notified to building control. The right liner type and size depends on the appliance and fuel.
A liner is what makes an old or oversized flue safe and efficient for a modern appliance. Here is when one is needed.
Chimney liners
- Jobsafe, sized inner flue passage
- Flexible typestainless steel for stoves
- Rigid typepumice or clay sections
- Needed whenflue damaged, oversized, leaking
- Sign-offHETAS or building control
What a liner does
An old chimney flue is often just brick or stone with mortar joints, sometimes unlined, and may be oversized for a modern appliance. A liner gives it a continuous, gas-tight inner passage of the right size, so combustion gases are carried out cleanly and at the right speed. This matters for three reasons: it stops fumes and tar leaking through cracked masonry into the building, it gives the appliance the draught it needs to run efficiently, and a correctly sized liner reduces condensation and tar build-up. For a wood-burning stove going into an old chimney, a liner is frequently recommended to match the flue to the stove's outlet.
Types of liner
The main options are flexible stainless-steel, rigid sectional and cast in-situ. Flexible stainless-steel liners are the common choice when retrofitting a stove — a coil is lowered down the existing chimney and connected to the appliance, and grades are matched to the fuel (with higher grades for wood and continuous burning). Rigid liners use pumice or clay sections, often built in during construction or major works, giving a robust permanent flue. Cast in-situ liners form a new lining inside the existing flue and can strengthen the structure as well as line it. The right choice depends on the appliance, fuel, flue route and the condition of the chimney.
| Liner type | Typical use | Notes |
|---|---|---|
| Flexible stainless steel | Retrofitting a stove | Common, grade matched to fuel |
| Rigid pumice / clay | New build or major works | Robust, permanent |
| Cast in-situ | Lining and strengthening | Forms lining inside old flue |
Indicative; the right type depends on appliance, fuel and flue. Sources: HETAS; Approved Document J.
When you need one and the rules
You are likely to need a liner if the existing flue is cracked, leaking or unlined, if there are signs of fumes or tar staining coming through the chimney breast, if the flue is too large for the appliance, or when fitting a new stove into an older chimney. Relining is controlled work under Approved Document J, which sets out flue sizing and construction. That means it must be notified — the simplest route is a HETAS-registered installer (for solid fuel) who self-certifies and issues a certificate, or a building control application if your installer is not registered. After installation the flue should be swept and checked and the work documented.
Frequently asked questions
Do I always need a liner to fit a wood-burning stove?
Not always, but a flexible stainless-steel liner is frequently recommended when fitting a stove into an old chimney, to match the flue size to the appliance and ensure a sound, gas-tight passage. An installer assesses the existing flue.
Is relining a chimney notifiable work?
Yes. Relining is controlled work under Approved Document J. It must be carried out and certified by a HETAS-registered installer for solid fuel, or notified to building control if the installer is not registered.
What is the sign that a flue needs relining?
Cracked or leaking masonry, fumes or tar staining coming through the chimney breast, an oversized flue causing poor draught, or fitting a new appliance to an old unlined chimney are all signs that relining may be needed.
Sources & further reading
- gov.uk — Approved Document J (combustion appliances and fuel storage systems)
- HETAS — flue liners and installation 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.