1. What is a Twin Wall Flue System?
A twin wall flue is a prefabricated chimney system designed for appliances like wood-burning stoves. It consists of two layers of stainless steel with insulation (usually ceramic wool or mineral wool) sandwiched between them.
This setup:
- Keeps external temperature low (safer to install near combustibles)
- Keeps internal flue gases hot (better draft and efficiency)
- Can be installed externally or internally, even where no chimney exists
- Quick to install compared to a clay flue built chimney
- Cost effect to build compared to a clay flue built chimney
- Ideal for room sealed installation + low energy homes
- Flexible installation, anywhere within the room
- Can be installed retrospectively
- Looks great – Stainless Steel or Powder Matt Black
2. Benefits of a Twin Wall Flue System
Absolutely — a twin wall flue system comes with a bunch of solid benefits, especially if you don’t have a traditional chimney or you’re doing a modern stove install. Here’s a breakdown of the key advantages:
1. No Existing Chimney Needed
- Perfect for homes without a brick chimney — you can install it internally or externally
- Gives you flexibility on stove placement (e.g. center of a room or in an extension)
2. Improved Efficiency
- The insulated design keeps flue gases hotter for longer
- A hotter flue = better draught = more efficient burning and less smoke backdraft
- Helps stoves reach operating temps faster, improving combustion and fuel economy
3. Safe for Use Near Combustibles
- The outer wall stays cooler, making it safe for use near walls, joists, and roofing
- Built-in insulation maintains a safe temperature on the outside of the pipe
4. Modular & Easy to Install
- Comes in pre-fabricated sections with twist-lock or clamp connections
- Can be assembled by a competent DIYer or professionally installed
- Easier and cheaper than constructing a new chimney
5. Minimal Downdraft & Condensation
- Maintains flue gas temperature, reducing the chance of downdrafts
- Insulation helps prevent condensation, which can cause corrosion over time
6. Versatile for Internal or External Install
- Can go up through ceilings and roofs or be run externally up an outside wall
- Ideal for retrofitting into older buildings or modern extensions
7. Low Maintenance
- With proper installation and regular sweeping, twin wall systems last for decades
- Stainless steel liners resist corrosion, soot buildup, and tar deposits
8. Highly Durable & Weatherproof
- Most systems are made of high-grade stainless steel (316L inner, 304 outer)
- External systems are designed to withstand harsh weather with proper flashing and terminals
9. Regulation Compliant
- Meets modern building regs and safety standards (e.g., UK Part J or CE/EN1856-1 compliant)
- Easy to get certified if installed by a HETAS or equivalent installer
10. Increases Property Value
- A properly installed stove with a twin wall flue can boost your home’s energy rating and resale value
- Adds a stylish, modern heating solution with a professional finish
If you're comparing it to other options like flexible liners, brick chimneys, or single-wall pipe, the twin wall is often the best all-rounder — especially when you're going for safety, efficiency, and flexibility.
Need help choosing the right size or planning a layout? Happy to help!
3. When to Use a Twin Wall Flue System
Great question — knowing when to use a twin wall flue system is key to getting a safe and efficient stove setup. Here's a breakdown of the situations where twin wall flue is the best (or required) option:
If your property doesn’t have a brick or masonry chimney, you’ll need a twin wall flue to create a safe, insulated chimney system from scratch.
Use case: New builds, extensions, garages, cabins, mancaves or homes with no chimney breast.
When running a flue outside the building (up an external wall), twin wall is essential.
- It’s insulated, so it prevents flue gases from cooling too quickly
- Maintains proper draft and prevents condensation
Use case: You want to install a stove near an external wall and vent straight out through it.
If your flue goes through upper floors or the roof, you must use a twin wall system to maintain safe clearances to combustibles.
- Safe around joists, plasterboard ceilings, and roof timbers
- Building regs require insulated flue in these cases
Use case: Stove is on the ground floor and the flue passes through the first floor and loft to the roof.
If your stove is freestanding in the middle of a room or not near an existing chimney, twin wall flue is used from the appliance upwards.
- Prevents excessive heat loss
- Looks clean and modern
Use case: Central island stoves, modern open-plan layouts, or glass garden rooms.
Twin wall flue pipes are designed to be installed with minimal clearance (usually 50mm) from combustible materials.
- Unlike single wall pipe, which needs far more clearance and cannot pass through walls or ceilings safely
Use case: You have limited space or are installing near timber studs or plasterboard.
Most local building codes require twin wall flue when:
- There's no existing chimney
- The flue runs through a wall, ceiling, or roof
- The installation is in a timber-framed or non-masonry building
Use case: Any stove install you want signed off legally and safely.
When NOT to Use Twin Wall Flue
- Inside an existing masonry chimney — here, you'd usually use a flexible flue liner
- Directly from stove to stove collar for short internal connections — you might use single wall stove pipe for the first 1–1.5 meters, then connect to twin wall
If you tell me a bit about your stove and setup (e.g., is there a chimney? Are you going through a roof or wall?), we can help you figure out exactly where and when to use twin wall in your system.
4. Key Twin Wall Components
Twin Wall Flue Pipe Sections
- Come in various lengths: 250mm, 300mm, 500mm, 1000mm, etc.
- Choose high-quality stainless steel (e.g., 316 inner, 304 outer)
- Ensure insulation is CE approved (usually 25-50mm)
Appliance Adaptor
- Connects stove collar to the first flue pipe
- Stove collars are usually 5", 6", or 7" — double-check your stove's outlet
Locking Bands
Secure pipe sections together; most systems use twist-lock or clamp bands
Elbows / Offsets
- For navigating around obstacles (usually 15°, 30°, or 45°)
- Minimize use where possible to maintain a good draft
Wall Brackets
Support the flue system every 1.5 to 2 meters on vertical runs
Support Plate / Ceiling Collar / Firestop
For internal installations through ceilings and floors
Flashing & Storm Collar
Seals roof penetration and prevents leaks
Terminal / Rain Cap / Cowl
Top cap to keep rain, birds, and debris out
5. Sizing Guide
Most domestic stoves use:
- 5” (125mm) flue pipe for appliances up to 5kW
- 6” (150mm) for larger stoves or when DEFRA/UK regs apply
Always follow manufacturer guidelines and local building codes.
6. Regulations & Safety – draw/draught & safety
The Twin Wall System does not always need to be higher than the apex of the roof. If coming up an external wall it generally needs to be between 600-1000mm above the guttering / fascia board. Check out stove manufacturers recommended flue height and comply with Building Regulations (UK Part J) or local code.
If coming through a roof, the top of the cowl needs to be 2.4m from the horizontal roof.
Safe distance from combustibles: usually 50mm.
Installation by heating engineer, HETAS installer or similar certified professional in your region is recommended.
7. Cost Estimate (UK Example)
| Item | Cost Estimate (GBP) |
|---|---|
| Flue pipe (1m section) | £90–£110 |
| Appliance adapter | £40–£90 |
| Elbows | £70-£90 |
| Roof flashing kit | £50–£100 |
| Terminal/rain cap | £75 |
| Full kit (average install) | £400–£1500 |
8. What to Look For When Buying
- CE or HETAS certified
- Reputable manufacturer (Duraflue, Poujoulat, Selkirk, Schiedel)
- Twist-lock or clamp-lock system for easy assembly
- Warranty (usually 10–25 years)
9. Installation Tips
- Dry-assemble everything before fixing
- Maintain vertical rise as much as possible
- Avoid too many bends or long horizontal runs
- Get professional advice for building penetrations
If you want, I can help you sketch a system layout or recommend parts based on your stove brand and house type. Just let me know your setup!
