How much does a twin-wall flue cost to install?

Typically £1,900 to £3,300 supplied and fitted, depending on the height, the number of floors and whether it runs inside or out. With a mid-range stove the whole job is around £2,600 to £4,800.

Can a twin-wall flue go up the outside of a house?

Yes. It leaves through the back wall at the stove and climbs the outside on brackets to above the roof line. It is quicker to fit but draws less well than an internal run.

Do I need planning permission for a twin-wall flue?

Usually not on a house, if it stays within 1 metre above the highest part of the roof. Conservation areas (front or road-facing side walls), listed buildings and flats are the common exceptions.

How far must a twin-wall flue be from wood?

The distance the flue maker states, often around 50 to 60 mm for good-quality systems. It applies at every joist, rafter and stud.

Can twin-wall go through a flat roof?

Yes, with a flat roof flashing. The height rules still apply, and on a flat roof the flue usually has to be taller to clear nearby walls and windows.

Twin-wall flue installation

No chimney does not mean no stove. A twin-wall flue is an insulated stainless steel chimney in kit form: one pipe inside another with insulation between, safe to run through a ceiling, a loft and a roof, or out through a wall and up the outside of the house. Supplied and fitted it usually costs £1,900 to £3,300, so a stove with a twin-wall flue comes to about £2,600 to £4,800 with a mid-range stove.

Flue supplied and fitted about £1,900 to £3,300

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Typical UK prices including VAT, checked November 2026.

When twin-wall is the answer

The house was built without a chimney. Most homes built since the 1970s, and many new builds, have no flue at all.
The stove is going in an extension, garden room or barn. Twin-wall lets the stove sit where you want it, not where a chimney happens to be.
The old chimney has been taken down or is beyond repair. Sometimes a new flue costs less than rebuilding a stack.
You want the stove in the middle of a room. An internal run through the ceilings keeps the flue warm and draws better than an external one.

What twin-wall costs

Item	What it covers	Typical cost
Twin-wall system, fitted	Flue sections, supports, fire stops, flashing, cowl and fitting the stove	£1,900 to £3,300
Stove and twin-wall together	With a mid-range stove	£2,600 to £4,800
Hearth	A ready-made plate, or a built hearth with wall protection	£150 to £1,000
Scaffold	Usually needed for an external run or a high roof	£300 to £600

Typical UK ranges including VAT, from national price guides read November 2026. Estimate your own job.

No chimney? Tell us where you would like the stove and a fitter can plan the flue route.

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Planning a twin-wall flue

A twin-wall flue is built from short sections that lock together. Inside the room the stove usually connects to a length of single-wall flue pipe, which then joins the twin-wall system before it passes through the ceiling. From there the flue runs up through each floor and the loft, inside fire stops and supports, and out through a roof flashing with a cowl on top. The alternative is a short run out through the back wall and up the outside of the house, fixed with wall brackets.

Inside or outside?

An internal run is warmer, so it draws better and condenses less, and it hides the pipe in cupboards or boxing on the upper floors. It costs more in carpentry and making good. An external run is quicker and keeps the upstairs untouched, but the flue is colder, it is on show, and the extra bends at the wall can hurt the draw. Fitters usually aim for no more than two bends of 45 degrees on a run.

How high the flue must go

Approved Document J sets where a solid fuel flue may come out of a roof. In short: within 600 mm of the ridge it must finish at least 600 mm above the ridge; elsewhere on a pitched roof it must be at least 1 metre above where it leaves the roof, or as high as the ridge, measured with a 2.3 metre rule; and it must be at least 1 metre above any opening window or rooflight within 2.3 metres. A flue of at least 4.5 metres from the stove is the usual guide for a good draw. Thatched roofs need much greater distances.

Clearances and fire stops

Each twin-wall maker states a minimum distance to anything combustible, often around 50 to 60 mm, and that distance has to be kept at every joist, rafter and stud. Where the flue passes through a floor or ceiling it goes through a fire stop plate, and through the loft it should be guarded so nothing can be stored against it. A notice plate records what was fitted.

Planning permission

For a house in England, a new flue is normally permitted development as long as it does not rise more than 1 metre above the highest part of the roof. In a conservation area, a flue on the front of the house or a side wall facing a road usually needs permission, and a listed building always needs listed building consent. Flats do not have permitted development rights. Check with your council if any of these apply, before buying the stove.

Building Regulations

A new flue and stove are notifiable under Part J. A HETAS-registered installer certifies the work; otherwise a building notice goes to the council before work starts.

Sources we used

Prices are typical ranges from national UK price guides for homeowners, read November 2026, including VAT. Rules are summarised in our own words as general information.

How it gets done

Most twin-wall jobs take two to three days, longer where ceilings need opening up and making good.

Plan the route
Stove position, joists, loft, roof covering and the exit height are checked.
Cut and support
Openings, fire stops and supports go in; the roof is flashed.
Build the flue
Sections are locked together up to a cowl at the right height.
Connect and certify
The stove is connected and tested, then certified and notified.

Common questions about stoves

How much does a twin-wall flue cost to install?: Typically £1,900 to £3,300 supplied and fitted, depending on the height, the number of floors and whether it runs inside or out. With a mid-range stove the whole job is around £2,600 to £4,800.
Can a twin-wall flue go up the outside of a house?: Yes. It leaves through the back wall at the stove and climbs the outside on brackets to above the roof line. It is quicker to fit but draws less well than an internal run.
Do I need planning permission for a twin-wall flue?: Usually not on a house, if it stays within 1 metre above the highest part of the roof. Conservation areas (front or road-facing side walls), listed buildings and flats are the common exceptions.
How far must a twin-wall flue be from wood?: The distance the flue maker states, often around 50 to 60 mm for good-quality systems. It applies at every joist, rafter and stud.
Can twin-wall go through a flat roof?: Yes, with a flat roof flashing. The height rules still apply, and on a flat roof the flue usually has to be taller to clear nearby walls and windows.

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