Do I Need a Flue Liner for My Log Burner?

When homeowners ask whether they need a flue liner, the honest answer — for the vast majority of existing UK chimneys — is yes. A stainless steel flexible liner is not an optional upgrade; it is a Building Regulations requirement for most log burner installations, and for very good reason.

We fit flue liners in homes across Poole, Bournemouth, and throughout Dorset every week. It is the single most important component of a safe, efficient installation — and the consequences of skipping it can be serious.

What Does a Flue Liner Actually Do?

A flue liner is a continuous, smooth-walled tube that runs from the stove's flue collar, up through the chimney stack, and terminates in a flue terminal or liner pot at the top. It serves four critical functions:

1. 1

   Containment of combustion gases

   The liner provides a sealed pathway for flue gases — including carbon monoxide, carbon dioxide, and water vapour — from the stove to the outside. This prevents toxic gases escaping into the room through cracks or porous brickwork.

2. 2

   Correct flue sizing for the appliance

   An old masonry chimney was designed for an open fire — which needs a large, open flue cross-section. A modern stove needs a correctly sized, smooth-bore flue to create the right draught. Connecting a stove to an oversized chimney without a liner creates poor draw, excessive condensation, and tar build-up.

3. 3

   Insulation and condensation management

   A correctly installed liner, particularly when wrapped in vermiculite or mineral wool insulation at the top, keeps flue gases hot enough to exit the chimney without condensing. Condensation of flue gases inside an unlined chimney creates acidic tar deposits that corrode brickwork and eventually cause chimney fires.

4. 4

   Structural protection of the chimney

   The liner protects the masonry from the corrosive effects of flue gases, extending the life of the chimney and protecting the surrounding structure from heat damage.

Why Do Most Existing Chimneys Need a Liner?

The vast majority of Victorian and Edwardian houses across Poole and Bournemouth have large masonry chimneys with open flues designed for coal and open fires. These chimneys typically measure 9" × 9" (225 mm × 225 mm) in cross-section — far too large for a modern stove's 5" or 6" flue outlet.

Additionally, after decades of use (or non-use), the mortar joints between the brickwork inside a chimney often degrade. Smoke and CO can pass through these joints into party walls or adjacent rooms. A liner bypasses this entirely by providing a sealed, smooth route for gases.

The only scenario where a liner might not be required is in a purpose-built flue system already correctly sized and certified for solid fuel — such as a factory-built insulated flue system in a new build. In practice, this is relatively rare.

316 vs 904 Grade Liner: What's the Difference?

Stainless steel flue liners come in two grades: 316 and 904. The grade refers to the alloy composition and its corrosion resistance.

5-Inch vs 6-Inch Liner: Which Do You Need?

The diameter of liner required depends on the stove's flue outlet size — specified in the manufacturer's installation manual — and the stove's heat output:

• • 5-inch (125 mm) liner: typically used with stoves up to about 5 kW with a 5" flue outlet. Common in modern compact stoves.
• • 6-inch (150 mm) liner: the most common size; used with most 5–12 kW stoves with a 6" flue outlet.

Never downsize a liner relative to the stove's outlet — this restricts draught and causes serious performance problems. Upsizing is sometimes acceptable but should be verified with the manufacturer.

What Does a Flue Liner Cost?

In Dorset, a complete flue liner supply and installation typically costs:

• • Single-storey chimney (up to 4 m): approximately £600–£800 including labour
• • Two-storey chimney (4–8 m): approximately £900–£1,300
• • Tall chimney with tight bends (8 m+): approximately £1,200–£1,700

When quoted as part of a full stove installation, the liner cost is usually included in the all-in price rather than quoted separately. Always confirm whether the liner is included in any quote you receive.

Insurance and Resale Implications

Installing a stove without a liner — or without the required HETAS certificate — creates a significant risk to your home insurance. Most building insurance policies require notifiable building work to be properly certified. An uncertified, unlined installation can invalidate your policy in the event of a fire or carbon monoxide incident.

When you come to sell your property, solicitors will ask for the HETAS certificate or Building Control notice for any stove installation. An installation without proper documentation will likely be flagged in the conveyancing process, potentially delaying the sale or requiring remedial work at your cost.