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If you are considering fitting home heating systems yourself, it helps to be mindful of the safety and productivity regulations while installing them. An important aspect of safety lies with adhering to twin wall flue regulations, which are designed to guide homeowners and installers in the proper installation and maintenance of twin wall flue systems. 

Twin wall flue systems, known for their dual-layer construction, provide a secure and insulated channel for directing exhaust gases from heating appliances out of a property. Adhering to these regulations not only ensures compliance with the complex building standards but also provides peace of mind by greatly increasing the safety and effectiveness of your heating systems. 

While it is not the most gripping of subjects, it is something you should be aware of for any installation of twin wall flue systems, either for new constructions or renovations.

What Is a Twin Wall Flue System?

If you are making the effort to research regulations, you almost certainly know what a twin wall flue system actually is. That said, for anyone who might be unfamiliar, let’s just quickly cover the basics before moving on to a breakdown of the regulations.

A twin wall flue system is a specialized chimney solution ensuring the safe venting of exhaust gases. This system is most commonly recognized by its double-layered structure, which includes an internal pipe that allows the passage of exhaust gases and an external pipe that encases insulation material between the two layers. 

This clever design ensures the maintenance of safe operational temperatures and prevents heat damage to any adjacent building structures by effectively containing the insulation material.

Systems like this are adaptable to various building types, both residential and commercial, making them ideal for properties without traditional chimneys or where internal routing is more challenging. Their versatility also extends to general compatibility with different fuel types, and because of that, there is a broad application range.

What Is the Purpose of This Guide?

Our intention here isn't to go into the small details - the current regulations are broad, highly detailed, and frankly cover intricacies that you will probably never need to be aware of. 

With that in mind, this guide looks at the core aspects of the UK Building Regulations (pertaining to twin wall flue systems) as more of an overview than anything else: the main things that you need to be aware of when installing twin wall flue pipes, encompassing the important elements. If you do not feel able to follow the building regulations, we always suggest getting a professional fitter to do the work for you.

Adherence to these basic regulations is not only a legal obligation but also a worthwhile measure to ensure the long-term safety and productivity of heating systems in homes and commercial properties. If you need the small details, you can find the current set of regulations here

That aside, the basics should be enough for most people, so let’s take a look.

Do You Need Planning Permission for Twin Wall Flue Pipes?

Typically, planning permission isn't required for installing a twin wall flue in the UK, except for listed buildings where altering the exterior appearance might need approval. For self-installed flues, notifying the local building control authority is mandatory. This is a subject we have covered quite extensively through this guide, please take a look if you would like to explore more information in greater detail. 

How Far From the Roof Must the Flue Be?

The regulation for flue height above a roof is guided by the '2.3-metre rule', stating the cowl should be horizontally distanced at least 2.3 metres from the roof. For ground-floor extensions (such as conservatories), the cowl should maintain this distance from nearby structures. 

While a total flue height of 4.5 metres is recommended for an optimal draw, there is no legal minimum height if the flue functions properly. In smaller structures like cabins or boats, shorter flues may be necessary due to support and height limitations, with well-insulated twin wall flues often functioning effectively at 3.5 metres.

Bend Limitations

In a twin wall flue system, the ideal setup is completely vertical, but adjustments may be needed for obstructions. At least 80% verticality is recommended for optimal performance. UK building regulations allow a maximum of four bends, each not exceeding a 45-degree angle. If four bends are used, a soot door is required for access. A 90-degree bend is permissible only in a rear connection to the stove, using a 'T' connection, and counts as two bends. This type of setup meets the safety standards perfectly.

Clearance for Twin Wall Flues

For a twin wall flue system, the required clearance from combustibles is usually specified by the manufacturer, although we might recommend a 70mm clearance in enclosed spaces and 50mm outdoors (approximately), depending on your system - our installation guides cover this in more detail.

This also differs from single-wall stove pipes, however. Due to lower insulation and higher temperatures, they typically require a distance of at least three times the pipe's diameter, as per building regulations. These clearances are important for safety reasons in twin wall flue installations, so please ensure you pay attention to them. 

A flue needs to be minimum of 600mm (60cm) away from any openable windows, doors and air vents,

Boxing in Twin Wall Flues

According to building regulations, a twin wall flue must be boxed in when passing through areas like cupboards, storage spaces, or roof spaces. This boxing ensures adherence to the required clearance from combustibles. This safety measure is integral to twin wall flue installations, aligning with regulatory standards for building safety.

Bottom Line

Again, the whole point of this article is to provide a concise overview of twin wall flue regulations in the UK, covering key aspects such as clearance to combustibles, boxing-in requirements, and the permitted number of bends. These are the most common aspects that you need to be aware of. More detailed information can be found in the Combustion Appliances and Fuel Storage Systems regulations.

If you need expert advice or high-quality twin wall flue kits, contact today. Our experienced team is ready to assist you daily from 8 am to 8 pm at 0800 279 02 74 or