How to Price Chimney Lining: Flexible Liner, Twin-Wall and Pumice Systems

Quick Answer: A flexible 904-grade stainless liner installation for a typical 8m two-storey UK chimney runs £600–£1,100 supply-and-fit, twin-wall insulated flue (no existing chimney) £1,800–£3,800, and pumice in-situ relining £2,500–£5,500. Building Regulations Part J, BS EN 1856-1/2 and HETAS registration apply throughout, and the system grade must match the appliance fuel and operating temperature.

Summary

Most UK chimney lining quotes split three ways: a stainless flexible liner pulled into a sound masonry stack, a twin-wall flue clad up an external wall or boxed internally where no flue exists, and a cast pumice or concrete relining where the chimney is structurally usable but the flueway has failed. Picking the wrong route is the single biggest pricing mistake — quoting flexible when the appliance is an open fire (illegal under EN 1856-2 designation), or pricing twin-wall when the customer expected the existing chimney to "just be lined", both result in lost jobs or money on the table.

This guide gives line-item costs for the three common systems, sweep and CCTV survey allowances, scaffolding, top-of-stack make-good, and the documents Building Control will ask for at sign-off. Numbers are England-and-Wales 2026, southern markets at the upper end. Scotland adds notification under the Building (Scotland) Regulations.

Pricing here assumes appliance-led installation by a HETAS-registered installer (self-certification) or by a non-registered installer with a Building Notice and an LABC inspection. Both routes are equally legal — but the LABC route adds £200–£450 in fees and a fortnight of programme time the customer rarely budgets for.

Key Facts

Quick Reference Table

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System Use Case Supply £/m Fitted £/m Typical 8m Job
904 flexible (150mm) Wood/multi-fuel into existing chimney £30–£55 £75–£135 £600–£1,100
904 flexible (125mm) DEFRA stove ≤5kW into existing chimney £25–£42 £65–£115 £550–£950
316 flexible (150mm) Gas appliance into existing chimney £15–£28 £55–£95 £450–£800
Twin-wall insulated (150mm) No existing chimney; external or internal run £85–£140 £160–£260 £1,800–£3,800
Twin-wall insulated (175mm) Larger output stoves / range cookers £110–£180 £190–£300 £2,200–£4,600
Pumice cast in-situ Failed Victorian flueway, structurally sound stack £180–£320 £280–£420 £2,500–£5,500
Sectional pumice (Isokern) New-build or full chimney rebuild £140–£220 £240–£380 £2,200–£4,200

Detailed Guidance

Flexible liner — when it's the right answer (and when it isn't)

Flexible stainless liner is the default for relining a sound masonry chimney serving a stove. The two grades to know: 316 is gas-only and corrodes when exposed to acidic condensate from wood combustion, while 904 is the multi-fuel grade with thicker, higher-nickel stainless steel. Quoting 316 for a wood-burner is a common cowboy move — six months in, the liner perforates and the customer's insurance won't pay because the install certificate listed the wrong designation.

Flexible liner is not legal for an open fire — only Class 1 chimneys (parging or rigid liner) can serve an open fire under Approved Document J. If the customer wants to keep the open fire and "just have it lined", the answer is pumice, not flex.

Diameter selection follows the appliance manufacturer's instructions, but a useful rule: 5kW DEFRA stoves take 125mm minimum, 6–8kW stoves usually 150mm, 9kW+ stoves and most older rigid-flue stoves need 150mm or 175mm. Never reduce diameter below the appliance flue spigot. Consult the flue liner installation guide for sizing tables.

Allow for backfill insulation on any flexible liner serving a wood-burner — vermiculite poured around the liner inside the masonry chimney keeps flue gas temperatures up, reduces creosote condensation, and is increasingly being treated as best practice rather than optional by HETAS sweeps.

Twin-wall flue — when there is no chimney

Twin-wall insulated stainless flue is the system used when the customer wants a stove in a property without an existing chimney — single-storey extensions, garden rooms, modern open-plan kitchens with no flue. The flue runs through the roof or boxed up an external wall, and every metre is engineered with a 25mm rockwool insulation layer between an inner and outer stainless skin.

Pricing is significantly higher than relining because every component is bespoke: support brackets, ceiling support plates, fire-stop plates, weatherproof flashings, storm collars and rain caps. A simple two-storey internal install runs £1,800–£2,400 on supply alone before any labour.

Distance to combustibles is the killer detail. Every twin-wall manufacturer specifies a minimum clearance from the outer skin to any combustible material — typically 50–80mm depending on the system. Where the flue passes through a timber floor or ceiling, a non-combustible fire-stop plate is mandatory. Quotes that don't itemise these components usually undercount the total.

Pumice relining — Victorian and Edwardian stacks

Pumice relining (cast in-situ, also sold as Isokern sectional or TecnoFlex flexible pumice) is the system for older brick or stone chimneys where the original lime parging has failed but the masonry stack is sound. Two routes:

Pumice is the only relining system that can serve an open fire as well as a stove, which is why customers with inglenook fireplaces who want to keep the option of an open fire end up here. It's the most expensive system because it requires a CCTV survey, a pre-pour sweep, scaffold to the pot, deflation/inflation kit, the pumice mix itself, and 24-hour curing time before the chimney can be returned to service.

Survey, sweep and access — the hidden third of the quote

A good chimney lining quote makes the access and prep visible to the customer. The components people miss:

Item Typical Cost Notes
CCTV chimney survey £120–£250 Inspect for breaches, soot deposits, bird nests
Pre-line sweep £55–£95 Mandatory before any liner is pulled
Scaffold to chimney £400–£700/week Often required for 1–2 weeks
Lead back-gutter or step flashing £180–£400 Where flashing is disturbed during work
Pot, cowl, anti-downdraught cap £85–£210 Specify cowl type — bird guards block stoves
Make-good to chimney breast / hearth £180–£600 Plaster, paint, hearth tiling
Carbon monoxide alarm £15–£35 Mandatory under Approved Document J

For homeowners — what should chimney lining cost?

Most homeowners hire a chimney lining installer alongside a stove install. A typical realistic budget for a 3-bed semi with an existing brick chimney getting a 5kW DEFRA stove and 8m flexible liner is £900–£1,400 for the lining alone, plus £600–£2,500 for the stove, plus £200–£800 for a hearth, plus £400–£700 for scaffold. Total install £2,400–£4,500.

If a builder quotes a flue lining at £400 on a wood-burner, they are almost certainly proposing 316-grade liner — say no. For solid fuel ask specifically for "904-grade, EN 1856-2 designation T600 minimum, vermiculite-backfilled" and request the HETAS certificate at handover.

Frequently Asked Questions

Do I need to line a chimney to install a wood-burning stove?

Only if the existing flueway fails inspection. Approved Document J says the flue must be in good condition, the right size for the appliance, and free from defects. A pre-installation CCTV survey will tell you. In practice, almost every Victorian or Edwardian chimney needs a liner because the original lime parging has failed and tar/condensate has eaten into the brickwork.

How long does a 904-grade liner last?

Manufacturer warranties are typically 10–25 years. Real-world life depends heavily on how the stove is used — slumbering a stove overnight on green wood produces acidic condensate that attacks the liner from the inside. Stoves run hot on dry wood with the air vents open, swept annually, can give 20+ years. Stoves run cold and damp give 5–8 years.

Can I reline a chimney that's been used with a back boiler?

Yes, but the chimney needs a more aggressive sweep first because back boilers cool flue gases significantly and produce heavy creosote deposits. A CCTV survey post-sweep is essential — back boiler chimneys often have severe internal erosion that flexible lining cannot bridge. Pumice cast-in-situ is sometimes the only option.

Does a customer need Building Regulations approval for chimney lining?

Yes. Approved Document J applies to any work on a flue. Two routes:

Without one of these, the work is not building-control compliant and will flag on a future house sale.

What's the price difference between top-down and bottom-up liner installation?

Negligible. Top-down (lowering the liner from the pot down) is more common and faster on straight flues. Bottom-up (pushing the liner up from the fireplace) is used on flues with offsets where the bullet-nose cone needs to be guided around bends. Same labour cost; the choice is determined by the chimney geometry, not pricing.

Regulations & Standards