1. What Is a Flexible Flue Liner?
A flexible flue liner is a corrugated stainless steel tube designed to be inserted down an existing chimney to safely carry away smoke and combustion gases from appliances like:
- Wood-burning stoves
- Multi-fuel stoves
- Open fires
- Gas or oil appliances (in specific versions)
It essentially turns an old or damaged chimney into a safe, properly sized flue system.
2. Why Use a Flexible Flue Liner?
-
Safety
Stops gases, smoke, and carbon monoxide from leaking into the house through cracks in old chimneys.
-
Efficiency
Improves draught and helps your stove burn more efficiently. Helps flue gases stay warm and rise quickly — less smoke, more heat.
-
Compliance
Required by building regulations in many countries when installing a stove. Necessary for chimney systems that aren’t already lined or are in poor condition.
3. When Do You Need a Flexible Flue Liner?
- You’re installing a wood burner, multi-fuel stove, or gas appliance into an existing masonry chimney
- The chimney is old, cracked, smoking into room, or unlined
- You want to improve draw/draught and reduce soot or tar buildup
- You need to meet local regulations (e.g., UK Building Regs Part J)
4. Choosing the Right Liner
1. Liner Diameter
- Match the stove outlet — typically 5" (125mm) or 6" (150mm)
- UK regs: 6" required for most wood stoves, unless it's DEFRA-exempt (then 5" is allowed)
- Never reduce diameter — can affect draft and void warranties
2. Liner Grade
Flexible Flue Liner is manufactured from Grade from 316L or 904L grade stainless steel.
- Can bend to fit narrow, uneven chimneys
- Usually installed with top plates, terminals, adaptors, and optionally, insulation
| Material Grade | Use For | Lifespan |
|---|---|---|
| 316L Stainless | Wood, multi-fuel (occasional use) | 10–15 years typical |
| 904L Stainless | Coal, wet wood, long daily use | 20+ years; more resistant to corrosion |
3. Liner Construction
- Twin-skin, corrugated stainless steel — flexible to fit old chimneys
- Inner wall is smooth to reduce tar/soot buildup
- Make sure it’s CE marked or HETAS-approved (UK) / UL-listed (US)
5. What’s in a Typical Flue Liner Kit?
A full kit will usually include:
- Flexible flue liner (cut to length)
- Top plate & clamp – holds the liner at chimney top
- Rain cap / terminal – stops rain and birds entering
- Adaptor – connects stove pipe to liner
- Register plate – seals bottom of chimney (optional but recommended)
- Bird guard – built into terminal or separate
6. Installation Basics
- Liner is fed down from the top down the chimney from the chimney pot
- Always install with arrow pointing UP (indicates smoke direction)
- Use vermiculite insulation or backfill if required
- Register plate at the bottom seals the chimney and supports soot cleanout
- Must comply with Building Regs (Part J in the UK) or local codes
7. Cost Estimate (UK Pricing)
| Item | Cost (Approx) |
|---|---|
| 316L liner (10m) | £280-£330 |
| 904L liner (10m) | £350–£450 |
| Full kit (5"–6") | £350–£600 |
| Installation (pro) | *£800 |
8. Benefits of a Flexible Flue Liner
- Safer and more efficient stove operation
- Reduces condensation, tar, and soot buildup
- Improves chimney draft
- Meets building and insurance requirements
- Extends life of your chimney
9. Common Mistakes to Avoid
- Using the wrong diameter
- Not insulating where required
- Incorrect installation direction (arrows should face up)
- Cutting the liner too short
- Not getting it signed off (required for compliance)
