Flue Heights

As one of the main purposes of a flue system is to remove the products of combustion from your home, it stands to reason that your chimney must be of a certain length and height to safely distribute these fumes up into the atmosphere and not into your neighbour’s upstairs window.

Building Regulations stipulate a minimum system length (stove collar to base of terminal) of 4.5m but that is the bare minimum to ensure a sufficient change in pressure for a draw to get started and the stove to even operate. Many environments, situations and stoves will require longer systems than this to perform at their optimum efficiency and heat output.

An added benefit of attaining a certain height with your flue system is the improved draw this will create. As you extend your flue you are extending the pressure difference which can only improve the draw and performance of the chimney and stove. This also ensures the draw is not impeded in any way by adjacent buildings and trees which will affect the direction of air across the top of your flue.

Approved Document J of the Building Regulations for England & Wales illustrates the heights you must achieve with your system however, if you find it hard to get your head around the jargon they use - and you are not alone! - then hopefully our illustrations below will help out.

2300mm is the magic number when it comes to flue heights as it doesn’t only apply to the horizontal distance between the system and the roof surface (pictured above). If there are any obstacles to the flue within 2300mm of it, such as windows in the roof or neighbouring buildings or structures, these need to be taken into consideration when determining how high to run your flue system:

• If you have an openable window in your roof and the flue will be within 2300mm either side of it or anywhere below it, then your flue system must rise above the window by 1000mm
• If a neighbouring building is so close that any part of it comes within 2300mm of your chimney system, your flue must rise above that part of the adjacent building by 600mm

We can even go one further and calculate just how high your flue will extend once through the roof surface, depending on the pitch:

• 25 Degree Pitch = 1070mm high.
• 30 Degree Pitch = 1330mm high.
• 35 Degree Pitch = 1610mm high.
• 40 Degree Pitch = 1930mm high.
• 45 Degree Pitch = 2300mm high.
• 50 Degree Pitch = 2740mm high.

For flue systems installed in single storey extensions and conservatories, 2300mm again comes into play. If the flue passes through the extension or conservatory roof within 2300mm of the house, then the full height of the house must be cleared by at least 1000mm (see first image above). However, if the flue is sited further away from the house, then only the minimum 4.5m flue system rule applies.

Should your roof be thatched or made of any other combustible material, then as you can imagine these distances must increase. As illustrated below, if your flue exits through the roof within Section A then you are required to rise at least 1800mm vertically above the roof surface AND at least 600mm above the ridge. Alternatively, if your flue exits within Section B then your vertical distance remains at least 1800mm and at least 2300mm horizontally from the roof surface:

It is worth noting that the distances highlighted above are minimum distances only and your system may be required to extend beyond these to create a sufficient draw.

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Comments

David Wantling says:
21st August 2019 at 1:04 pm
I think that something is wrong here because 2300mm above the ridge of the roof is completely impractical, and apart from requiring a properly engineered support bracket it will look really strange above a bungalow roof.

Andrew Shuttleworth says:
31st January 2020 at 10:45 am
It’s 2300mm horizontally back to the roof surface from the top of the flue. Not 2300mm above the ridge.

Justin Langford says:
13th August 2020 at 7:49 am
Why does it say 2300 above ridge in last diagram. This diagram and writing underneath needs rewriting correctly

Andrew Shuttleworth says:
13th August 2020 at 9:24 am
Apologies for any confusion, this has been amended to read ‘horizontally’ rather than ‘vertically’.

Adam Bird says:
8th November 2020 at 11:14 am
Hello, I have a side extension (to just below you upstairs window sill on your picture) does the flue in my extension have to go above main roof height? 600mm? Adam Bird

Andrew Shuttleworth says:
9th November 2020 at 8:41 am
That depends on where you are siting your stove and running the flue system. If the flue is within 2.3m of the main body of your house, then you do have to take into consideration the full height of the house, running the flue up past the roof line and adhering then to the rules within the image with regards to height.

Vicky says:
14th July 2021 at 4:30 pm
Hi if my neighbor has installed a flue on the side extension next to house where do I measure the 2300mm from please?

Andrew Shuttleworth says:
15th July 2021 at 8:01 am
You are taking the measurement from the point the flue passes through the roof of that side extension (internal system) or passes the roof line of the extension (external system). If that point is within 2300mm of any structure, the flue system must rise high enough to clear it.

Richard Hillman says:
5th August 2021 at 2:38 pm
Is there a maximum height for a flue liner? We have a very tall house and want to install a wood pellet burner in the basement which would mean a flue height of about 14m. Your article gives a minimum and says that more height = more draw but is there a maximum please?

Andrew Shuttleworth says:
6th October 2021 at 1:50 pm
Our Helix Premium Flue liner is certified to be installed to a maximum of 20m.

Bob Stevens says:
15th November 2021 at 5:28 pm
I have a glass single storey pitched roof structure fixed on to our orangery (1? higher). 3m away is a second storey window. How high does the flue have to be above the glass roof

Andrew Shuttleworth says:
16th November 2021 at 12:43 pm
This depends on how far from the main body of the house (and that window) your flue systems exits through the glass roof. If you are within 2300mm of the house, then you must run the flue system the entire length of the property and up above the roof line. However, if your flue system is further than 2.3m from the house, you can technically disregard the building and that window but practically speaking, you will experience an issue with smoke and so I should seek the advice of a HETAS registered installer to advise further on this install!

Pete Smith says:
16th November 2021 at 4:58 pm
May I ask, are there any explicit regs regarding trees? A neighbour is building a new house with a fireplace chimney that will terminate approx 600mm from our boundary (horizontally). We have a large tree – about 10 metres tall – that is 600mm into our side of the boundary, but slightly offset to the north – so the distance from trunk to flue centres will be about 1500-1800mm, but any branches could well grow to within 600mm of the flue horizontally & be taller than it & will still be on out side of the boundary, so the neighbour can’t legally prune them back any further. I would think that it’s a crazy place to put a chimney, but profit usually trumps common sense, so are there any hard & fast rules they should obey – either building regs or fire regs? The roof will be tiled & pitched, the chimney is on a brick-built external cavity wall. Thanks, Pete.

Andrew Shuttleworth says:
25th November 2021 at 5:06 pm
Anything within 2300mm of a flue system should be taken into consideration and if that was a building rather than a tree, then your neighbour would have to be clearing the height of it with their installation. The close proximity of those trees will also have an impact on the draw/operation of their stove and flue as it impacts wind patterns and pressure across the top of the chimnney. Their installer should definately be taking this into consideration with the build.

marion Murphy says:
23rd November 2021 at 2:52 pm
How high can the flu be above the gutter line as my neighbour is complaining that smoke is going into her conservatory that’s 3 meters away. At the moment it’s about 2 meters above.

Andrew Shuttleworth says:
25th November 2021 at 4:58 pm
A flue system can be as high as you desire as long as you use sufficient brackets and supports (recommended approx. every 2m). You can use Guy Wires and Brackets in conjunction with Structural Locking Bands on every joint above the roof line for extra stability.

Tom says:
11th December 2021 at 5:40 pm
Hi, we’ve got a single storey flat roof, the installer went for min flue height of 4.5m, I’ve never seen a flue that far above the roof, it looks like we’re on a ship! It mentions above that the building regs suggest 4.5m, but i can’t see it anywhere in Part J, is there any room for manoevre? I’ve read elsewhere that 3.5 or even 3m min length is possible for eg a shed. The flue twin lined 5?, any advice greatly appreciated.

Andrew Shuttleworth says:
13th December 2021 at 11:00 am
The 4.5m minimum flue length is a building regulation requirement to ensure sufficient draw can be established to power the stuff as efficiently and effectively as possible however, if an installation doesn’t allow for this, it can come down to the discretion of the HETAS approved installer as they are responsible for testing and certifying the system. It may be the case here that less than 4.5m would not have been sufficient for your stove to operate cleanly and your installer was only happy at 4.5m.

Lee Catlin says:
19th January 2022 at 10:31 am
I live in a detached bungalow and have no buildings and neighbours within 150 meters of the property and the property backs on to a field do I still have to adhere to the 4.5 meter rule

Andrew Shuttleworth says:
19th January 2022 at 10:58 am
The 4.5m rule is an advised length of flue system required to sufficiently (and efficiently) operate a solid fuel appliance and has no correlation to the proximity of neighbouring buildings. Below 4.5m and a sufficient draw may be created by the flue system to power the burner. Your HETAS registered installer will advise and sign-off on the length of flue system required for your installation. Neighbouring properties or buildings within 2.3m of the flue terminal affect the height your system must travel (because you would need to clear the height of anything within this distance) but as you say, this is not an issue for your installation.

Neil Ingram says:
28th January 2022 at 10:57 pm
Hi, I have a single story extension and am thinking of installing a burner in the far corner which will be 3.5m away from the body of the main house. The internal height to the ceiling there will be approx. 2.5m or 1.5m from the top of the burner, so does this mean that my flue will have to extend 4.5m from there or 3m above the extension roof? Many thanks in advance

Andrew Shuttleworth says:
31st January 2022 at 9:37 am
The 4.5m minimum flue length rule-of-thumb is from stove top to terminal and so in your instance, you will require at least 3m above the extension roof (to attain an overall flue length of 4.5m). Please bear in mind however, 4.5m may still not be long enough to create the required draw for your chosen burner or the environment in which you are installing but this will all be discussed with and tested by your HETAS approved installer.

Matthew Hennessey says:
18th February 2022 at 2:26 pm
Hi, I have a question regarding boxing in or shielding of twin wall as it passes through an upstairs bedroom. Does this require boxing in, as the reg suggests it should only be in storage areas?

Andrew Shuttleworth says:
21st February 2022 at 12:53 pm
Boxing in of Twin Wall flue systems as they pass up through a property is only required in storage areas as you say, typically the loft. This is to prevent combustible materials and objects from resting against the hot sides of the flue system when put (or ‘tossed’) into the loft. It is advisory to cage or box a system in the upstairs also however as a safety measure for similar reasons.

Justin says:
5th April 2022 at 6:33 pm
Hi, My neighbour has recently had a wood burner installed in their single storey extension with a pitched roof. The flue comes up through the roof at a height of approximately 1200mm and our property is approximately 1000mm from the flue. We have a velux in our extension pitched roof which is 1700mm from the flue which I’m sure isn’t within regs? The flue height is also approximately the same height as the top of our second floor bedroom window which is around 3000mm which again I’m sure isn’t right? Surely the flue would have to be taken above the main roof of the house so fumes would hopefully not be a problem as we can smell fumes within our kitchen (velux) and bedroom when they have it on. Could provide photo if needed? Look forward to your reply.

Andrew Shuttleworth says:
6th April 2022 at 4:14 pm
Under Approved Document J of the Building Regulations (England & Wales), a flue system is required to clear the height of any structure that is within 2.3m of it. Therefore, if your neighbour’s flue system runs closer to your home than 2.3m, then they are required by law to increase the height of the system until it clears your roof line by at least 1000mm to avoid the very situation you describe; smoke pouring into adjacent windows etc.

Bruce says:
24th April 2022 at 9:52 am
Hi having a two story extension done,am wanting to run the flue on the gable end straight up the middle to the roofline,my new gable end sits 3.5m away from the original roof line of the house (new extension slightly lower in roof height) so am I right in thinking the flue only has to go 600mm above the apex of the roof line on my new gable end? Many thanks

Andrew Shuttleworth says:
25th April 2022 at 4:15 pm
Yes, as you are within 600mm of the ridge/apex, you are only required to clear this by 600mm (plus you are over 2.3 from the original roof line). However, always double check this with your HETAS installer as they will be the responsible person signing off the work. If you do not already have an installer, you can find one through the link below. https://www.hetas.co.uk/find-installer/

Kathryn says:
22nd July 2022 at 12:08 am
Someone else already asked about woodburners and neighbours trees. We have just moved into a property built in 2016. The next door neighbour has a large beech tree which even if cut back to their boundary will be within 4 foot of the flue. The woodburner has never been used we now realise this is probably because the fire can’t be lit without risking burning the house down. The woodburner was fitted by a HETAS registered fitter and passed by building control VERY frustrating .

Andrew Shuttleworth says:
26th July 2022 at 9:34 am
The brand of Twin Wall flue you have installed will have a certified safe clearance to combustible materials (i.e. the neighbour’s tree). This should be no more than 50mm-60mm typically so as long as the tree is further away from the systen than that, there shouldn’t be an issue. Also, that safe clearance to combustibles is more concerned with flue systems running through the home, passing close by to wooden joists, rafters and the like. An external system would be far cooler than this so again, shouldn’t be an issue.

Eddy says:
29th October 2022 at 5:05 am
Hi, I have a single story extension and am thinking of installing a burner in the far corner which will be 3.5m away from the body of the main house. But the neighbour next to me have a loft do I have to go all the way up on the loft or I can go 3m from my flat roof

Andrew Shuttleworth says:
29th October 2022 at 9:37 am
You need to clear anything within 2.3m of that flue, be it your property or a neighbours. If your neighbour’s loft is within this space, then you will have to rise above that but even if it is not, you would need to consider the proximity of that with regrads to your emissions blowing into their home.

Eddy says:
1st November 2022 at 8:57 pm
Thank you for replying to me My neighbour will be 15 feet away from my extension

Bill Clark says:
1st November 2022 at 8:37 pm
I am planning a 5KW wood burning stove with a 6 inch external TW flue which will run vertical in my 2-story house. The flue will joggle round my gutter using two 45 degree bends. The roof has a central ridge with each side being 30 degrees. The sketches in Part J would only appear to be applicable to flues passing through the roof. Can my flue terminate say 1 Meter above the gutter? Regards, Bill Clark

David Campbell says:
2nd November 2022 at 3:49 pm
Hi, I am considering having a wood burner stove in my single storey extension adjacent to my main house ,(floor to roof ridge 4m 200 mm high )and looking at possible places to site the stove, my preferred choice would result in the flue outlet going through my pitched 30degree tiled roof at a point 2 metres from the ridge but within 2,300 of my main house, roughly same as point B on document J plan for flues The flue would need to extend 600mm above the tiled roof weather surface , to make it level with my single storey ridge roof, but as my main house pitched roof eaves is another 700 mm higher up and falls within 2m300mm range , how high would my flue need to be in total to comply with the regs. Many thanks

Andrew Shuttleworth says:
3rd November 2022 at 4:22 pm
Because you are planning to exit the extension roof within 2.3metres of the main two storey house, the flue system will have to clear the full height of the house. If you wanted to send a rough sketch to [email protected] we could assist you with designing the full flue system.

Tracy Sane says:
20th December 2022 at 1:27 am
Hello, How does someone determine where to place a stove and flue within a room with a two story open cathedral ceiling, approx 45’ angle roof pitch. I’m wanting the back of the stove to be about 3 feet away from an outside wall, gable end. How do I determine where to place the flue, ie. near the ridge,, closer to the eaves, somewhere in between?

Andrew Shuttleworth says:
30th December 2022 at 1:12 pm
It really would come down partly to personal preference and also to location suitability for the flue system. We would advise visiting http://www.hetas.co.uk and searching via your postcode to bring up registered installers in your area. Contact a couple and request a site survey, they would then be able to advise you further on the most suitable location for your stove based on the property.

Peter Simpson says:
15th March 2023 at 8:01 am
If the flue is mounted externally on a gable wall (not near the ridge), so that its not penetrating the roof, does the min 2.3 m horizontal clearance rule still come into play, or is it only the 1 m clearance? (i.e. for a 45deg pitched roof would the min clearance above the gutter be 1 m or 2.3 m? Thanks.

Andrew Shuttleworth says:
16th March 2023 at 11:27 am
Both rules will apply for this however, whilst the top of the last length of flue pipe must have a horizonal clearance of 2.3 meters, this will also need to be at least 1000mm up OR as high as the ridge. From what you have described as you are far from the ridge, providing you are both 1000mm up and 2.3m away from the roof line, your clearance will comply with the current UK Building Regulation.