Choosing the Right Flue Diameter for Your Wood Burner

RHINO
Aug 26
2 min read

Introduction

When installing a wood burner, one of the most important decisions is choosing the right flue diameter. The size of your flue pipe directly affects draft, safety, and stove efficiency. Getting it wrong can lead to poor performance, smoky fires, and even dangerous carbon monoxide leaks.

Why Flue Diameter Matters

The flue pipe is responsible for removing combustion gases from your stove. If the pipe is too narrow, gases may not escape properly, causing smoke to back up into the room. If it’s too wide, the draft can weaken, leading to incomplete combustion and heat loss.

Standard Flue Size Requirements

Most stoves up to 20kW – Require a 150mm (6-inch) flue as standard.
DEFRA-approved stoves under 5kW – Often allow for a 125mm (5-inch) flue.
Open fires – Require a minimum of 200mm (8-inch).

5 Inch Single Skin Flue Pipe

6 Inch Twin Wall Flue Pipe

Always check your stove manufacturer’s instructions before installation.

Factors to Consider

Stove Output – Higher output stoves usually need wider flues.
Flue Length & Height – Taller chimneys may perform better with slightly smaller diameters due to stronger natural draft.
Insulation – Uninsulated flues lose heat faster, which can weaken draft. Twin wall systems help maintain heat.
Building Regulations – UK regulations (Document J) specify minimum flue diameters depending on stove type.

Expert Tip

If you’re retrofitting into an existing chimney, a flexible flue liner is often the best solution. It ensures the correct diameter is maintained throughout, improving efficiency and safety.

Conclusion

Choosing the right flue diameter is key to getting the best out of your wood burner. If in doubt, consult a HETAS-qualified installer to ensure compliance and maximum performance. At Rhino Flues, we stock a full range of flue pipes, liners, and twin wall systems to suit every installation.