Chimney Liner Calculator
Size a chimney liner from appliance output and flue height.
About Chimney Liner Calculator
Appliance flues follow the outlet size rather than being calculated, while open fires need around a tenth of the opening area. Each bend reduces effective height and therefore draught. Oversizing a liner cools the flue gases, which reduces draught and increases condensation, so bigger is not safer with chimneys.
Formula
Chimney Liner
Open fires need a flue about a tenth of the opening area; appliances follow their outlet size
- one tenth rule
- Open fireplace flue area of roughly 10 per cent of the opening
- draught
- Stack effect, which grows with effective chimney height
Worked example
With the default values below, Chimney Liner Calculator returns Liner Diameter Required of 150. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Appliance outputminimum 0.1 kW
- 8 kW
- Chimney heightminimum 1 m
- 7 m
- Appliance typeone of Wood stove, Gas appliance, Pellet stove, Open fireplace
- Wood stove
- Fireplace opening areaminimum 0 m2
- 0.5 m2
- Number of bendsminimum 0
- 2
Results
- Liner Diameter Required
- 150 mm
- Flue Cross-Sectional Area
- 17,671 mm2
- Liner Length Required
- 7.95 m
- Draught Rating
- Adequate natural draught
- Insulation Backfill Volume
- 84.0 L
Step by step
- 1Values used
- 2Chimney Liner
- 3Liner Diameter Required= 150 mm
- 4Flue Cross-Sectional Area= 17,671 mm2
- 5Liner Length Required= 7.95 m
- 6Draught Rating= Adequate natural draught
- 7Insulation Backfill Volume= 84.0 L
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Chimney Liner calculated?
Open fires need a flue about a tenth of the opening area; appliances follow their outlet size Appliance flues follow the outlet size rather than being calculated, while open fires need around a tenth of the opening area. Each bend reduces effective height and therefore draught.
Why does Chimney Liner matter?
Oversizing a liner cools the flue gases, which reduces draught and increases condensation, so bigger is not safer with chimneys.
What values do I need to enter?
This calculator takes 5 inputs: Appliance output, Chimney height, Appliance type, Fireplace opening area, Number of bends. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.