Any work that affects an existing chimney (including installation of a stove or flue liner) or creates a new chimney is considered building work and so falls withing the remit of the building regulations department of the local authority.Document J

The government issue an approved document, which contains practical guidance on ways of complying with the requirements of the building regulations, which deal with combustion appliances. In the UK, Document J of the building regulations applies to flues and chimneys. These must be adhered to for safety and legality.

If you want to get a twin wall flue pipe fitted in the UK, then no, you don’t usually need planning permission under normal circumstances. The main exception here is if you have a listed property. Listed properties in the UK have a few different types (grades). For all listed properties, you’ll need permission for new flue pipework of any kind.

If you want to fit the twin wall flue yourself in England and Wales, then you need to contact the local council planning department or building control and check the building regs. You need to tell them when you have completed the work so that they can come and inspect it.

We recommend that you communicate heavily with the local council before you make all your decisions on your stove installation and double or even triple-check all the details. You really do not want to be getting headaches late on in the process of this. That will be expensive and time-consuming for you - much better to deal with details early in the planning stages when it is not stressful.


Important note: HETAS engineers 

If you choose to hire a HETAS engineer to fit your, they are certified to handle all the necessary regulations for twin wall flues on your behalf. However, if you require planning permission for the installation, it is important to consult with your local council. The council will be able to provide guidance on the specific planning requirements for your area and ensure that you comply with any regulations or restrictions that may apply.


How far do I need the flue above the roof?Height of flue above the roof

One of the main regulations regarding how far your flue should be above your roof is the ‘2.3-metre’ rule.

The magic number here is “2.3”. You need your flue to be 2.3 metres directly above the roof. If you want to install it on the ground floor, in a conservatory, or in an extension, then you need to keep the cowl 2.3 metres from any buildings that are close by. 


How Tall Should My Twin Wall Flue Be?

Your twin wall flue should be a total of 4.5 metres or more. You need this much to maximise the draw you get from your flue system. The good news is that there is no legal requirement for the chimney's height, so this part is up to you - yes, this means you can choose. This number is just a guide for you...

You get really good insulation with twin wall flues. This means that you often don’t need the full height and that 3.5 metres mostly works well, if you have an installation for less-standard constructions like a cabin, boat, yurt or some kind of ground-floor barn.

For installations in buildings such as cabins, yurts and boats, a 4.5-metre flue isn’t possible, as it would become too high to be properly supported. So in some cases, a shorter flue is preferable.


Twin wall flue system: How much vertical pipe?

If you want the perfect twin wall flue system then you ideally want it 100% vertical. But, we live in the real world, so of course, you sometimes need to adapt.

You can cut the pipes and make angles for them - no problem. This can get you around most things in your way. So, it is ok to use pipes cut at an angle to allow you to bend around any obstructions. In general, for your combustibles to be safely rising out of your home, you want 80% of the piping to be vertical for it to run without any problems. This is generally safe, but there is no official standard on this.


UK Twin Wall Flue System: How many bends?bends in a flue

UK building regulations limit you to four bends in your twin wall flue system.
The angle of these bends can’t exceed 45 degrees. If you do have four bends, you must have a soot door in your flue pipe somewhere in between them to give you access.

Okay, this is where it gets a bit more complicated, but only slightly. Your bends can be a maximum of 45 degrees on each one. If you have 4 bends, then you need a soot dour for access.


Some Extra Things To Consider…

While these aren’t strict regulations, we do think these are a few important things you need to know as part of your flue-pipes research:


What is a Soot Door?

A soot door, also known as an access door or cleanout door, is a small door or panel located on a chimney or stovepipe that provides access for cleaning and removing accumulated soot and debris. It is typically installed near the base of the chimney or stovepipe where the greatest buildup of soot and creosote occurs.

Soot doors can be made from a variety of materials such as cast iron, stainless steel, or ceramic, and can be either hinged or removable. Regular cleaning of the soot door is also important and Soot doors should only be opened by trained professionals who have the proper equipment and expertise to safely remove the accumulated soot and debris.


What is a chimney cowl? 

A chimney cowl is a device that is attached to the top of a chimney to improve its performance and protect it from external elements. It can be made from various materials such as stainless steel or galvanized steel.
The main purpose of a chimney cowl is to prevent wind from blowing down the chimney, which can cause poor draft and backflow of smoke into the room. It can also prevent rain, snow, and debris from entering the chimney, which can cause blockages and reduce efficiency.


What is single skin vitreous pipe?

Single-skin vitreous pipe is a type of stove pipe that consists of a single layer of steel coated with a layer of vitreous enamel. It is typically used in flue pipework for use in situations where the pipe does not need to be insulated.

It is used frequently in most solid fuel appliances for the first section of flue from the stove to the chimney, where it is exposed to the highest temperatures. It is available in various diameters to suit different stove models and is typically used in conjunction with other types of flue systems such as flexible liners or rigid insulated flue systems.

Regular cleaning and maintenance of the single-skin vitreous pipe is necessary to prevent the buildup of soot and other combustion byproducts that can reduce its efficiency and increase the risk of chimney fires.


Okay, Your Twin Wall Flue System Can Actually Have a 90-Degree bend...
So the four bends rule isn't strictly a four bends rule

If your stove is connected at the rear then you are actually allowed a 90-degree bend, but it counts as two 45-degree bends in your planning.


What is the distance to combustibles for a twin wall flue?

In plain English, "distance to combustible" is how close your system is to things that can catch fire (combustible materials). The distance to combustibles required for a twin wall system varies depending on the specific manufacturer's installation instructions and local building codes. However, as a general guideline, you need a minimum clearance of 50mm to combustibles.

This means that your twin wall flue needs to be installed at least 50mm away from any combustible materials such as wood, insulation, or plasterboard.
In some cases, a greater clearance may be required depending on the type and thickness of the combustible material, the temperature of the flue gases, and the specific installation requirements.

You really need to pay attention to the manufacturer's installation instructions and local building regulations to determine the specific distance to combustibles required for your twin wall flue system. Failure to comply with these requirements can result in a fire hazard and may void any warranty or insurance coverage.


Twin Wall Flue Pipes: Do I Need To Box Them In?Boxed in twin wall flue

As per the building regulations, a suitable guard is required to be installed when a chimney passes through a cupboard, storage space or roof space. This implies that during the installation of a twin wall flue system, it is necessary to properly encase it when passing through any of these areas while ensuring a safe distance is maintained from combustible materials.

It should be noted that these regulations represent only a few of the essential requirements for the installation of a twin wall flue system, and it is advisable to refer to the complete Document J Building Regulations document to ensure full compliance with all regulations.


Any work that affects an existing chimney (including installation of a stove or flue liner) or creates a new chimney is considered building work and is within the remit of the building regulations department of the local authority.

If you are going to do any work on an existing chimney by installing any kind of flue liner, stove, wood burning stove, then you are doing building work, according to the UK government. This means you need to contact your local council to check that you are complying with local regulations. Along with all the usual things you would expect, there are now an increasing number of smoke-free zones in the UK and so it is not always automatic that wood burners and certain combustion gases are permitted, from an environmental point of view.

Your go-to document on this topic is called "Document J". This is a guide from the UK government that helps you to understand the ways you need to comply with all the building regulations with regard to the use of combustion appliances in the home. This has specific attention to chimneys, flues, and combustible materials. It is really important that you make sure you understand all these (sometimes slightly odd) building regulations. As we mentioned before, it really is advisable to double-check that you understand all the relevant details to whichever flue pipe solution you are planning on using, as fixing these issues after implementation can lead to expensive fixes!



Do I need to line my existing chimney?Lining of a chimney

If your house was built after 1964, it is likely to have a concrete or clay inner liner for your chimney, which means that you may not need to reline it unless there are issues with your existing system. However, for older houses with exposed brick chimneys, there is no legal requirement to line them unless they are leaking, but there are benefits to lining them such as improved draw, reduced risk of chimney fires, and peace of mind from having a sealed system.

Before installing a stove, it is important to have the existing chimney/flue swept clean and checked for any damage or blockages. You can use a smoke pellet to check for leaks or blockages or consult a local chimney sweep for expert advice on the condition of your chimney.

We recommend that chimneys in older properties be lined as an extra precaution. It is important to notify building control before installing any chimney unless you are a certified HETAS engineer who can self-certify the installation. This will ensure that your installation meets all necessary building regulations and is safe for use.


Flue sizes

If you are in the UK and have a stove, the flue outlet will typically be located at the top or rear of the stove and measure either 5" (130mm) or 6" (150mm) in diameter. The first section of flue from the stove to the chimney usually requires a corresponding sized vitreous enamel flue pipe. However, for the rest of the flue system, a minimum of 6" (150mm) flexible chimney liner or rigid insulated flue system is typically required.

If you decide to purchase a flexible liner kit or a full twin wall flue system from, it will come equipped with the necessary adapter to connect to the 5" or 6" enamel pipe. This arrangement applies to most solid fuel appliances except for DEFRA Approved stoves, which have a 5" (130 mm) flue outlet. DEFRA Approved stoves produce fewer smoke particles than other stoves and, as a result, can be legally used with a 5" (130 mm) chimney liner or full flue system.


Did We Miss Anything? 

Hopefully, you just got all the answers you need, but maybe you still have a question. If you want to know about this or any other topic relating to domestic burners and flue pipes, then please check out our FAQ page.

Here is our guide to UK regulations or our installation guide.

If you have a more specific problem, or you need your purchase sorted out quickly, then take advantage of our years of experience and head to head to our contact page.