Fitting a wood burner is one of the most satisfying home improvements you can make, but the flue liner is where most installations succeed or fail. Choose well and the stove lights easily, burns cleanly and keeps you on the right side of building regulations. Choose poorly and you'll be fighting smoke roll-out, poor draw and a chimney that soots up twice as fast as it should.

Why the Liner Matters More Than the Stove

The stove is the visible part; the liner does the quiet, constant work. Its job is to carry flue gases safely up and out of the building while keeping heat in the flue and keeping condensation, tar and smoke out of the masonry. On an older UK property, especially one with a 9-inch brick flue, the original chimney was designed for an open fire burning coal. It's usually far too large for a modern stove, and it often has cracks, mortar gaps and leaks that let cold air in and smoke seep into bedrooms.

A correctly sized, insulated stainless steel liner solves all of that at once. It reduces the flue's cross-section so gases stay hot and move quickly, it seals the path so nothing escapes into the fabric of the house, and it gives you a smooth, easy-to-sweep surface. In most UK homes, the liner is the single biggest factor in how well the stove performs.

Stainless Steel: Grades, Sizes and the 316/904 Question

For solid fuel, stainless steel is the sensible default. You'll see two grades quoted most often, and the difference matters:

• Grade 316 — suitable for wood and most smokeless fuels. A good all-rounder and the most common choice for domestic wood burners.
• Grade 904 — more resistant to corrosion and better suited to coal, high-sulphur fuels and especially damp or coastal conditions where the flue will be challenged.

Wall thickness matters too. Liner walls of around 0.6 mm are typical for flexible liners, but thicker walls resist damage during sweeping and last longer. Cheap, thin liners are a false economy; replacing one means paying for the installation twice.

On diameter, the common mistake is going too big. A 5-inch (125 mm) liner suits most stoves up to around 5 kW output, and a 6-inch (150 mm) liner covers the majority of larger domestic stoves. Your stove's manual and the manufacturer's flue outlet size should guide you, but the general rule is to match the stove outlet and not exceed it unnecessarily. Oversized flues run cool, and cool flues tar up.

Insulation and Chimney Position

An uninsulated liner in an external chimney breast is a cold pipe. Warm flue gases hit cold metal, slow down, and deposit creosote and water. Insulating the liner — either with a wrap-around sleeve or by backfilling the void with vermiculite — keeps gases above the dew point and dramatically improves draw.

Where the chimney runs inside the heated envelope of the house, insulation is still worthwhile but less critical. Where it's on an outside wall, on a gable end, or in a bungalow with a long exposed stack, treat insulation as essential rather than optional. It also reduces the risk of condensation staining the chimney breast and of tar leaching through the plaster.

Chimney height and termination also affect draw. As a working guide, the flue should extend at least 4.5 metres from the stove to the terminal, and the outlet should clear the roof line and any nearby openings, dormers or neighbouring structures in line with the current building regulations and the relevant British Standard. Too short a flue, or one sitting in a downdraught zone, will smoke back no matter how good the stove is.

Twin Wall, Flexible and Rigid Systems

Not every installation uses a flexible liner dropped down an existing chimney. Where there's no suitable masonry flue, a twin wall insulated stainless system is run internally or externally instead. It's more expensive and more visible, but it performs superbly and is often the only compliant option for a new extension or a house without a chimney.

Rigid sections are useful for straight runs and for the final connection through the register plate and into the stove collar. Most good installations are hybrids: flexible liner through the chimney, rigid or adjustable sections at the bottom where the flue meets the stove, and a proper terminal and cowl at the top.

At the bottom, the register plate or closure plate seals the chimney opening around the flue. It should be rigid, sealed and preferably insulated, with a small access hatch if you want to sweep through it rather than from the stove.

Fuel, Sweeping and Long-Term Care

The liner you choose and the fuel you burn are linked. Seasoned wood with a moisture content below 20 per cent burns hot and clean; wet wood sends litres of water vapour and tar up the flue, which is exactly what corrodes liners and blocks terminals. A simple moisture meter is one of the cheapest bits of kit you can own.

Have the flue swept at least once a year for wood, and twice for smokeless fuel or if you burn a lot. Use a registered sweep who will report on the liner's condition. Watch for warning signs between services:

• Smoke spilling into the room when you open the stove door.
• A dull, sluggish fire that won't draw even with dry wood.
• Soot or tar deposits visible at the terminal or around the register plate.
• Damp patches or staining on the chimney breast.

Fix these early. A blocked or damaged flue is a carbon monoxide risk, not just an inconvenience, and every solid fuel installation should have a working CO alarm in the same room as the stove.

Get the liner right, insulate it properly, burn dry wood and keep up with sweeping, and your stove will reward you for years with easy lighting, steady heat and a chimney that stays clean. It's the least glamorous part of the job and easily the most important.