Flue Liner Length Calculator
Ordering too little flue liner means a delayed installation while you wait for more, while ordering far too much wastes money on materials you will not use. Enter the height from your stove or appliance outlet to the chimney pot or terminal below to get a sensible length to order.
Work out how much flue liner you need
Enter the height from the stove or appliance flue outlet to the chimney pot or terminal.
Allowing 10% extra for bends, offsets and connections, you should order approximately:
7m of flue liner
That covers a working length of around 6.6m, rounded up to the nearest whole metre since liner is typically sold by the metre or in rolls.
Recommended products
A few well-reviewed chimney and stove accessories to consider.
£25.26
Pros
- Heat-powered — no batteries or electricity needed to run
- Circulates warm air further into the room from a wood burner
- Includes a clip-on thermometer to monitor safe operating temperature
Cons
- Only starts spinning once the stove top reaches operating heat
- Sits directly on the stove top so placement can be fiddly
£26.99
Pros
- 18 flexible nylon rods extend to 24ft for tall chimney flues
- Two brush head sizes included for different flue diameters
- Hex shank drill adapter speeds up power sweeping
Cons
- Manual sweeping still needed to dislodge stubborn creosote build-up
- Best used with dust sheets to protect the room below
£19.99
Pros
- Toughened iron poker, brush, shovel and tongs on a sturdy stand
- Matte black finish suits both traditional and modern hearths
- Keeps all the everyday stove tools together and off the floor
Cons
- Stand footprint needs enough hearth space alongside the stove
Frequently asked questions
Why do I need extra flue liner beyond the straight-line height?
Chimneys are rarely perfectly straight, and bends, offsets and the connections at each end all use up extra liner, so it is sensible to allow a margin above the raw vertical height when ordering.
What flue liner diameter should I use with my stove?
The correct diameter depends on your stove's flue outlet size and the appliance manufacturer's instructions, so check these carefully before ordering as using an undersized liner can affect performance and safety.
Should I round up or down when ordering flue liner?
Always round up to the nearest whole metre, since liner is typically sold by the metre or in fixed-length rolls and running short partway through installation means an awkward extra joint or a second delivery.
Do I need a professional to fit a new flue liner?
Fitting a flue liner and connecting it to a stove or fire is safety-critical work, so it should be carried out or checked by a competent, registered installer such as a HETAS engineer.
How this calculator works
The calculator uses a simplified formula based on the ‘rise and fall’ principle required for optimal chimney draft. It takes into account the vertical distance (rise) between your stove throat and the chimney pot, plus an additional length to accommodate the necessary fall – typically around 10-15% of the rise, depending on chimney design and obstructions. This fall allows smoke to flow freely upwards without creating a stagnant pocket.
The calculator assumes a standard ‘square’ flue liner (100mm x 100mm) and calculates the linear length required. It doesn't account for specific stove types or complex chimney configurations, so always consult with a qualified HETAS registered installer for detailed advice before purchasing your flue liner.
Flue Liner Dimensions & Performance - A UK Guide
- **Internal Chimney Diameter:** Most standard wood-burning stoves require a minimum internal chimney diameter of 100mm (4 inches). Larger diameters may be needed for higher output stoves or if your existing chimney is significantly larger.
- **Flue Liner Type:** Consider the type of liner. Single wall liners are more affordable but offer less protection against heat and corrosive gases. Double wall liners, costing around £80-£150 on Amazon UK, provide superior insulation and are recommended for modern, high-efficiency stoves.
- **Rise & Fall Angle:** Aim for a rise/fall ratio of 1:8 to 1:10 – this means for every 1 metre of rise, you’ll need approximately 8-10 metres of fall. Too much rise without sufficient fall creates a ‘dead leg’ and hinders draft.
- **Chimney Pot Height:** The taller your chimney pot, the greater the linear length of liner required. Ensure accurate measurement of the pot height – even small discrepancies can impact performance.
- **Stove Throat Dimensions:** Measure the internal diameter of your stove’s throat accurately. This is where the flue liner connects and needs to be a precise fit. Typical diameters range from 80mm to 125mm.
- **Obstructions:** Any obstructions within the chimney, such as bird nests or debris, will increase the required liner length. Consider a chimney sweep before installation.
- **Fuel Type:** Solid fuel stoves typically require steeper fall angles than smokeless stove designs. Confirm your fuel type’s requirements.
- **HETAS Regulations:** All wood-burning stove installations must comply with HETAS regulations. Consult the HETAS code of practice for detailed guidance and to ensure a safe installation – available online or via their helpline.
- **Flue Liner Length Ranges (Approx):** For chimneys up to 10m, expect liner lengths between 2.5m and 4m. For chimneys exceeding 10m, significantly longer liners (4m - 6m+) will be needed.
- **Cost Comparison:** A single-wall flue liner can cost around £40 - £80 on Amazon UK, while a double-wall liner typically ranges from £80 - £150. Factor in the price of professional installation if required.
Worked example: Measuring for a Traditional Stove
Let’s calculate the flue liner length needed for a traditional wood-burning stove with a chimney height of 12 metres. The stove throat diameter is 100mm (4 inches). Using the calculator, we input these figures and obtain a calculated liner length of approximately 3.75m. This figure includes a 15% fall on the 12m rise.
The resulting 3.75m flue liner would be purchased from Amazon UK – expect to pay around £65 for a single-wall liner in this length. It’s crucial to allow for minor variations and consider ordering an extra 300mm (0.3m) to account for bends and connections. Remember that this example is simplified; always seek professional advice before installation, particularly if your chimney has unusual features or complexities.
More questions answered
What happens if I measure the rise incorrectly?
Incorrectly measuring the rise will lead to an inaccurate liner length. If you overestimate, you’ll have excess liner; if you underestimate, it won't fit properly. Double-check your measurements and use a reliable tape measure.
Does this calculator account for complex chimney designs?
No, this calculator assumes a simple ‘square’ flue configuration. Complex chimneys with multiple branches or unusual angles will require a professional assessment to determine the correct liner length.
What is the ‘dead leg’ and why does it matter?
A ‘dead leg’ occurs when there isn't enough fall in your chimney, creating a stagnant pocket where smoke can accumulate. This can lead to dangerous carbon monoxide build-up. The calculator helps avoid this by ensuring sufficient fall.
Should I always buy the longest liner?
No, buying an excessively long liner is wasteful and increases installation costs. Use the calculator to determine the precise length needed for your specific chimney configuration.
Can I use a different type of flue liner?
While this calculator is designed for standard square liners, you can technically use other types (round, oval) but it’s crucial to consult with a HETAS registered installer who can advise on the correct dimensions and installation method.
What if my chimney pot isn't perfectly vertical?
Even slight deviations from a perfectly vertical chimney pot will affect the liner length. Measure accurately, considering the angle of the pot when calculating the rise.
Do I need to insulate the flue liner?
Insulating your flue liner is generally not required with modern single-wall liners but is crucial if using older designs or in colder climates. Double-wall liners provide inherent insulation.
What tools do I need for accurate measurement?
You’ll need a reliable tape measure (at least 10m long), a level, and ideally a laser distance measurer for greater accuracy – these are readily available on Amazon UK from around £25.
Is it okay to slightly reduce the fall angle?
While technically possible, significantly reducing the fall angle can negatively impact draft performance. Aim for the recommended 1:8 to 1:10 ratio for optimal operation.
What if I’m unsure about any aspect of the installation?
Always consult a qualified HETAS registered installer – they have the expertise and knowledge to ensure your wood-burning stove is installed safely and efficiently. You can find installers through the HETAS website or via Amazon’s service providers.