How to install a wood stove chimney through a wall or roof

(Non-chimney installs)

Quick Step Guide to Non-Chimney Installations

1) Start your system with a length of Single Wall, Vitreous Enamel Stove Pipe in the same diameter as the outlet on the stove.

2) Connect a Single to Twin Wall Adapter to convert from this Single Wall Pipe to insulated Twin Wall Pipe a minimum of 150mm before reaching any surface (ceiling or wall).

3) The remainder of the flue system must be in insulated Twin Wall Flue Pipes only from this point onwards.

4) For internal systems passing up through the property, you shall require Joist Supports and Ventilated Fire Stop Plates for every ceiling the system passes through.

5) For external systems rising up the outside of the property, this must pass through the wall at no greater than 45° with a Wall Sleeve lining the passage through the wall itself. Another 45° Elbow or Tee Piece can be connected once through the wall to turn the system vertically.

6) Joist Supports are sufficient for supporting an internal system with Adjustable Wall Brackets providing the support for an external system every 2m maximum.

7) For internal systems, a Roof Support, Silicone Flashing and Storm Collar are necessary for safely passing through any roof type.

8) Once through the roof Surface (internal) or past the roof/gutter line (external), Twin Wall systems must attain a minimum vertical height of 1m to create a minimum horizontal clearance of 2.3m.

9) Finish off any system with a choice of Rain Caps or Anti-Wind Cowls.

What Is a Non-Chimney Installation?

Planning a brand new flue system may seem daunting at first but with this guide we hope to remove the mystery of creating a twin wall installation to suit your home, avoid the common pitfalls and understand Approved Document J of the building regulations in language we can all understand (highlighted in bold).

If you do not have an existing chimney in your home to install a wood burning stove into, a new class 1 chimney system needs to be created using Twin Wall (or Double Skin) insulated flue pipes. This Twin Wall flue system will either run internally (up through the floors of the property and exiting through the roof surface) or externally (passes out through an external wall and rising up the outside of the building, clearing the gutter line), depending on your preference and the room in which you wish to locate your new stove.

Why Do I Need To Use Twin Wall Flue Pipes?

The three main benefits of starting a flue system with single wall pipes are they tie in with the traditional aesthetic of a log burner, can withstand the temperatures produced in the outlet collar due to the enamel and they transfer a lot of heat to the outside of the pipe, maximising the heat output produced by the stove. However, it is for this very reason that it is unsafe and even illegal to pass a single wall pipe through a wall, ceiling or roof as the outer surface will become far too hot and may transfer that heat into nearby combustible materials such as joists and furnishings.

This is where Twin Wall flue steps in. As the name suggests, these pipes feature separate inner and outer skins with a layer of insulation between to prevent heat transfer to the outer edge of the pipe, making them safe to run through any surface type and compliant with Approved Document J of the current Building Regulations. By keeping the gases within the flue warm, this encourages the draw to continue rising and prevents cooler air outside from negatively affecting this

How to start your insulated flue system

No matter the flue system you are going to create, they should all begin with a length of Vitreous Enamelled, Single-Wall Stove Pipe. This will measure the same internal diameter as that of the outlet collar of your stove (5” or 6” are standard but it may be 7” or 8”) and will slot inside the collar via the male spigot at the bottom end of the pipe. And the male, narrow spigot must only be at the bottom of the pipe and not the other way around, no matter if it seems to fit better upside down as you will not be able to connect your Single to Twin Wall Adapter to the wrong end. The diameter of the outlet collar is the minimum diameter for the entire flue system and you can never reduce this. Simply seal this connection with at least 1200°C heat resistant cement or silicone sealant. We supply industry leading brands such as Vitcas, Kos and Envirograf for this very job.

It is possible to skip this step and connect the Twin Wall flue directly to the outlet collar with an Adapter however, this may over time tarnish the finish of a stainless Twin Wall pipe or remove the coating entirely from a black Twin Wall pipe.

Also important to bear in mind; hot gases want to rise and therefore a straight vertical length at the start of the system encourages this. The sooner your gases hit a bend in the flue, the less able they will be to negotiate through it without depositing soot and possibly slumping back down the chimney so exiting the top outlet of the stove is ideal but you are allowed to exit the rear outlet via a Single Wall 90° Tee Piece if necessary.

Which Twin Wall Adapter Do You Require?

As much Single Wall pipe can be used from the stove as required (but should be kept to a minimum) but you must convert from this to Twin Wall insulated flue a minimum of 6” (150mm) prior to reaching the underside of your ceiling / roof or inside of your wall.

The crucial building regulation to consider at this point regards the internal diameter of your flue system. The minimum internal diameter for a flue system when you reach the Twin Wall section is 6” (150mm) and this is easily attained by selecting the correct Single to Twin Wall Adapter. It is a common misconception that a system increases when it converts from Single Wall to Twin Wall flue simply due to the change in the overall size of the pipe but this is incorrect. We are only concerned with the internal diameter of the system and so to maintain the same diameter throughout (i.e. 5” to 5”) you require a Single to Twin Wall Adapter and to increase the diameter (i.e. 4” to 5”, 5” to 6” etc) only then do you require an Increasing Single to Twin Wall Adapter.

The only exception to this rule is for DEFRA approved stoves. Due to the cleaner burning nature of these models, they alone are permitted to remain at 5” diameter for the entire flue system and still comply with Approved Document J of the Building Regulations.

Now your system has begun correctly and you have successfully made the conversion from Single Wall pipe to Twin Wall insulated, you must plan the route your flue will take; internal, external or a mixture of both.

How To Install a Wood Burning Stove Chimney Through a Wall (External)

The first common error made when installing a wood burning stove chimney through a wall is that you can exit out from the rear of the stove and run horizontally, directly through the wall to the outside. This is incorrect as there must be no horizontal runs totalling greater than 150mm in length in a flue system or 90° (right angle) turns. Again, this is due to hot gases needing to rise and if forced to travel horizontally, they shall lose their heat, deposit soot in the pipe and hit the right angle turn like a barrier and slump back down the system.

To comply with the building regulations, a 90° Tee Piece (or elbow) can only be used directly in the rear outlet of the stove and absolutely nowhere else in the system. All bends can be no greater than 45° to allow the gases to continue rising freely and use these sparingly as you are limited to a maximum of 4 turns per system.

There are 4 Twin Wall items necessary to safely pass your system through an external wall; 45° Wall Sleeve, two Finish Plates and a Fixed or Adjustable length of Twin Wall pipe, long enough to pass clear through the wall whilst rising at that crucial 45° angle. The Sleeve protects both the pipe and the material of the wall from the thermal expansion of the pipe and the Plates tidy everything up inside and out. This is only applicable for passing through standard, non-combustible cavity walls. Should the wall consist of combustible materials (i.e. a wooden structure, you must allow for a safe clearance all the way around the flue of 60mm although this does vary depending on the brand of Twin Wall used).

Now your Twin Wall system has successfully exited the property, we need to turn the system vertically which is easily achieved with (ideally) a 135° Tee Piece & removeable Cap or a 45° Elbow. The benefit of the Tee Piece & Cap is it allows essential access to the external run of flue for cleaning and draining of condensates and rain water. The 45° Elbow does not offer this access.

For the optimum draw on your stove and compliance with the building regulations, the overall length of your flue system must attain a minimum length of 4.5m from stove outlet to Rain Cap. This does not pose an issue for chimneys on two storey homes but must be considered for shorter installs such as conservatories and summer houses. Depending on the length of flue selected for running through the wall dictates how far outside the system will sit from the outer surface. Quite often, this is only 50-80mm between outer wall surface and the pipe for aesthetic purposes and use with the shortest (and cheapest) Wall Brackets.

There are two important points to consider when calculating the lengths of Twin Wall flue required to successfully (and legally) run the system up the outside of your property wall; 1) the overall height of the finished flue 2) do you need to negotiate around any obstacles such as windows or overhanging soffits? Remember building regulations only allow for a maximum of 4 turns in the entire chimney and 2 have been occupied already (before and after passing through the wall), therefore you can only use 2 more elbows to create an offset around an obstacle, usually the gutters / soffits. Should you find you have other obstructions then the chimney will need to be re-sited unfortunately.

The only form of support typically required for an external Twin Wall system are Adjustable or Fixed Wall Brackets secured to the outside wall of the property, securing the flue system every 2m at very most. These brackets can be either fixed at 50mm or adjustable such as 50-80mm, 80-130mm, 130-210mm (that’s distance from wall to pipe) or longer still but for long external runs of 4m or more, it is highly recommended to secure an Adjustable Base Support at the bottom of the system as an extra anchor for the long run of Twin Wall above in addition to the Brackets. For supporting a flue past the roof line, there is a selection of Guy Wires, Stays and Structural Locking bands.

How High Must a Flue System Rise?

The final aspect of your flue system is ensuring you attain the necessary overall height and choice of suitable terminal…

For an external Twin Wall system rising up any wall other than a gable end, you must consider two building regulation requirements:

  • The flue must rise high enough to create a 2.3m horizontal clearance between the top of the last length of pipe and the surface of the roof


  • It must rise at least 1000mm once passed the roof line / soffits / gutter (basically, the lowest section of the roof surface) OR as high as the ridge

If rising up a gable end, the above still applies but with one caveat:

  • If the system passes the edge of the roof within 600mm of the ridge itself, then the system must rise at least 600mm above that ridge

A couple of additional points that often occur concern adjacent buildings and dormer windows:

a) If the system looks due to terminate below a window in a pitched roof or within 2.3m horizontally of any openable window, sun light or dormer, then you must extend the system 1000mm above the window

b) Any adjacent buildings within 2.3m of your flue system must unfortunately also be cleared. The flue will have to rise at least 600mm above the highest point on the adjacent building

And finally, simply secure a Rain Cap, Anti-Wind Cowl or any choice of Twin Wall terminal available in your range of Twin Wall. These are fairly straight forward to understand but please bear in mind, no Rain Cap is water tight and Anti-Wind Cowls are only advised for longer systems that create a sufficient draw and are located in open or exposed areas such as hillsides, by open land or waterfronts.

How To Install a Wood Burning Stove Chimney Through a Roof (Internal)

A typical internal Twin Wall flue system starts identically to that of an external system from the stove collar to the Twin Wall Adapter, as outlined above. From this point however, we are not heading through a wall but rather travelling up through the floors of a building to eventually exit through the roof surface.

For each ceiling / joist you are to pass through, there are 3 essential components to purchase; 2 Ventilated Fire Stop Plates and a Joist Support. Sometimes sold as a ‘Fire Stop Spacer’, Ventilated Fire Stop Plates must be secured into the ceiling or the floor whenever the system exits and/or enters a habited space. Basically, this boils down to requiring these plates everywhere except for the floor of the attic but even there it is recommended. And why ventilated plates? This is to ensure cool air can pass between the floors keeping the outer edges of the flue as cool as possible but still delaying the potential spread of fire. Solid Fire Stop Plates are for gas systems only. And as the name suggests, the Joist Support screws to each joist and forms a bracket for the system roughly every 2.5m. Therefore, in a typical two storey home, you shall require 4 Ventilated Fire Stop Plates and 2 Joist Supports.

No matter which type of system is being installed, any joints between pipes must be accessible and not buried within walls or joists and the Twin Wall must be boxed or caged in on the upper floors.

The most effective form of flue system is a vertical, internal chimney however, you do have up to 4 bends or turns allowed within the system should you need to negotiate around an obstacle along the way in the form of 45° Elbows (never 90°) and a Roof Support should be used on the rafters as a final form of support.

It is now time to pass the Twin Wall flue through the roof surface itself and there are three important stages to this:

Firstly, remember there is a safe clearance to combustible materials that must be maintained around all twin wall flue and so a 6” Twin Wall pipe will require a hole measuring approx. 320mm across (60mm clearance + 200mm outer diameter of pipe + 60mm clearance).

Secondly, selecting the correct Flashing for your roof is critical. The Flashing itself is a silicone or EPDM rubber cone that sits atop a base (traditionally lead but more likely aluminium these days) and can be cut back to tightly grip around the flue to provide a weather proof seal on the roof. However, Flashings do not need to be confusing as they basically fall into one of only two categories; either suitable for a tiled/slate roof or not. Flashings for tiled roofs have a large base which needs to be secured underneath the tiles whereas Flashings for every other roof type (flat, corrugated, wooden etc.) has a small base designed to be secured on top of the roof surface.

Thirdly, combine your Flashing with a Twin Wall Storm Collar to sit approx. 100mm above the Flashing as an extra layer of protection against the elements.

How High Must a Flue System Rise?

And the final aspect of your flue system is ensuring you attain the necessary overall height and choice of suitable terminal…

For an internal Twin Wall system rising up through the roof surface, you must consider all four of the following building regulation requirements:

  • The flue must rise high enough to create a 2.3m horizontal clearance between the top of the last length of pipe and the surface of the roof


  • It must rise at least 1000mm once through the surface of the roof


  • If the system passes through the roof surface within 600mm of the ridge itself, then the system must rise at least 600mm above that ridge
  • If the system looks due to terminate below a window in a pitched roof or within 2.3m horizontally of any openable window, sun light or dormer, then you must extend the system 1000mm above the window

And finally, simply secure a Rain Cap, Anti-Wind Cowl or any choice of Twin Wall terminal available in your range of Twin Wall. These are fairly straight forward to understand but please bear in mind, no Rain Cap is water tight and Anti-Wind Cowls are only advised for longer systems that create a sufficient draw and are located in open or exposed areas such as hillsides, by open land or water fronts.

18th February 2015



24th September 2016 at 1:00 pm
what about roofelt how do you seal it to pipe

Richard Fewings says:
24th September 2016 at 2:48 pm
Thanks very much for your enquiry. I have passed this on to our Customer Services Team who will respond to you directly and provide you with the advice needed.

David Wakeling says:
14th November 2016 at 7:55 pm
Im costing to install a Hwam 2360 in my bungalow with a top mounted flue direct up (no bends). I cannot find any information telling me if I should purchase a 5? or 6? flue system. Which one should I be costing?

Richard Fewings says:
15th November 2016 at 10:49 am
Thanks very much for your enquiry. I have passed this on to our Customer Services Team who will respond to you directly.

Mike Blake says:
31st December 2016 at 1:47 pm
My ‘Orangery’ type conservatory will have a 500mm (external) brick pillar in the corners, including where the log-burner will sit. This is obviously a twin-course plus insulation space pillar, rising up from the dwarf-wall that goes all around the base of the conservatory. The roof is complex (all glass, double-hipped i.e. pyramid design) so, I want to take the single-wall pipe vertically from the stove-top, then kink 135 degrees, go through the small area of wall that it the brick pillar and kink 135 outside, back to vertical and go 1m above the Consersatory roof (this will be happening 4m from the house). I know from your site that I need to use a converter to connect twin-wall to my vertical pipe 4? before I enter the wall. So, my question is, will the pillar be thick (wide) enough ? I could I ‘move the window-frames along’ and have another brick-width on the side on the pillar that I will put the twin-walled pipe through and 1 brick-width less on the pillar by the house wall (which is already 1.5m wide). Any other thoughts ? Thanks.

Peter Harris says:
19th January 2021 at 10:28 am
Hi. I am experiencing poor burning and fumes into the room. And glass blacking up. My Woodburner was installed with a Horizontal flue from the rear, through the wall, and then a 90 degree bend. Well over 150 mm in Length. Is this an illegal installation. Many Thanks

Andrew Shuttleworth says:
23rd June 2021 at 3:51 pm
I’m afraid that is an illigal installation unless your installer performed a draw test and received confirmation from the flue manufacturer that what they wished to do was acceptable (sadly, I suspect neither of these happened). There should be no horizontal runs in a flue system and no 90 degree turns. Both of these are hinderences to the draw which is resulting in your poor burning, fumes leaking into the room and blackening glass. The stove and draw are simply not getting up to temp.

J P Rose says:
29th August 2017 at 6:48 am
Hi I think that I understand the installation of the flue and wood burning stove , what I am unsure about is the type of house that we have got was built in 1986 app it has a open fire ,I believe it is called a fire box as it has got a damper there is a flue that appears to sit on on top of it .this I am told is a Parker flue system ,it looks like they are in metal sections,I have been told these are filled up with clay balls it also sounds very heavy at the top there is what looks like a square chimney stack I have not got a clue about this . How do I remove it ? Thanks for any suggestions. J P Rose

Andrew Shuttleworth says:
3rd January 2019 at 2:27 pm
Our advice in these situations would always be to contact a local HETAS registered installer to visit your property and advise on how best to remove the existing system

17th November 2017 at 7:14 am
Can your H pot 150mm/200mm be used onto an existing Dinak system of the same diameters?

Andrew Shuttleworth says:
3rd January 2019 at 2:28 pm
When it comes to the compatibility of Twin Wall, you must stay within the same brand I am afraid and so this Convesa H-Cowl will not connect to a Dinak flue system.

John Hole says:
26th November 2017 at 6:43 pm
Do you do anything suitable for a summer house a complete kit is what we are looking for

Andrew Shuttleworth says:
3rd January 2019 at 2:23 pm
We offer an extensive range of stoves perfectly sized for a summer house and can advise on a safe and effective twin wall flue system

C chewter says:
17th December 2017 at 9:22 am
The outside of my wall where the pipe passes through is cemented round the flue i hear bangs when it is cooling down is this ok

Andrew Shuttleworth says:
3rd January 2019 at 2:21 pm
Banging is not typical and I would advise you seek the assistance of a HETAS registered engineer. It may be that the incorrect plaster has been used and you are not allowing for the thermal expansion and contraction of that pipe.

Greg L Robertson says:
14th October 2018 at 6:37 am
After my flue passes thru the wal does the chimney have to go staright up? or can it angle off for a few feet? Instead of going thru my roof overhang can I angle out to the edge of the overhang then up the rest of the way?

Andrew Shuttleworth says:
3rd January 2019 at 2:20 pm
You are permitted a maximum of 4 turns in any one flue system and typically as far as an external Twin Wall flue system is concerned, these would be used 1 inside and 3 outside; 1 to turn the sytem vertically and 2 to negotiate around guttering or soffits etc.

Kate SCOTT says:
19th October 2018 at 10:00 am
Do you recommend using/ installing the ‘optional’ external air intake at the back of the stove, or is this not really necessary? I’m struggling to find out much info for this.

Andrew Shuttleworth says:
3rd January 2019 at 2:18 pm
It really depends on which stove you are interested in and where you are installing. External or Direct Air allows for a constant supply of fresh air for your fuel but not utilising it wil mot impact on the performance of your stove necessarily.

Gaby says:
20th January 2019 at 11:55 pm
My twinwall flue is going through a wall. When using a 45 degree wall sleeve, should I pack it with Rockwool between the sleeve and the flue pipe, and leave a 60mm airgap around the outside of the sleeve. Or should I leave an airgap between the sleeve and flue pipe and pack Rockwool around the outside of the sleeve?

Andrew Shuttleworth says:
26th July 2019 at 3:43 pm
You can fill the gap between the Twin Wall Pipe and the Wall Sleeve with rockwool but most keep this gap clear.

Tom says:
21st October 2022 at 3:37 pm
Can you clarify, is 60mm clearance required on the outside of the wall sleeve?

Andrew Shuttleworth says:
21st October 2022 at 4:07 pm
No, not the wall sleeve. That can sit flush to the wall and allows the pipe passing through to expand without damaging the fabric of the wall. The 60mm clearance to combustibles applies to pipe work only.

Roy Stokes says:
9th September 2019 at 5:45 am
Hi My question is – My Hetas engineer states that the maximum sideways distance I can move from the vertical is 20% of the total height. i.e. for my 6.2 metre chimney I can only travel 1.4 metres sideways. This measurement is along the 45 degree line? (not horizontally)? To exit the room & travel through the wall at 45 degrees takes about a metre so he is saying I can only move the flue about 0.4 metres in sideways direction. I see many flues outside at 2 metres with similar height.

Andrew Shuttleworth says:
31st January 2020 at 10:44 am
Your installer is absolutely correct. The building regulations concerning offsets and turns in a system states the distance travelling in the offset must not exceed 20% of the overall length of the system. This is because hot gases only want to rise and every turn or not vertical section of the flue is a hinderence or obstruction to that. And if gases are not rising, they are colling, losing their power and depositing soot etc within the system. That measurement is indeed along the 45 degree line (NO horizontals are permitted) and just because you see other flues like that, does not mean they are safe, legal or working well.

nick says:
20th September 2019 at 3:23 pm
I want to go from 7? vitreous to 7? twin wall as high up before the ceiling as possible (it goes into loft space) – any idea how I can do it? Would it make it different if I use skimmed fireboard rather than plasterboard (timberjoists) for the ceiling?

Andrew Shuttleworth says:
31st January 2020 at 10:41 am
You must convert from Single Wall Pipe to your Twin Wall a minimum of 150mm from the underside of that ceiling.

Mark Phillips says:
27th January 2020 at 4:07 pm
Hello I have a brick built fireplace where the log burner will be installed but i need to pass the vitreous pipe through the internal brick skin (behind the log burner) then a 100mm cavity and a 100mm dense concrete block at an angle of 45 degrees the vitreous pipe will then connect to a twin wall pipe in a new built chimney (this is where the register plate will be) . Do i need to use a liner to pass through this internal wall or can the hole be sealed to the vitreous pipe. Thanks Mark

Andrew Shuttleworth says:
31st January 2020 at 10:16 am
As long as you are only passing directly from a stove, through the wall of a chimney and into the cavity, then this is the only occassion you are permitted to use single wall pipe through a surface of any kind but we do not supply a wall sleeve for this, only the Twin Wall sleeves which will measure a minimum 7.5? diameter. Also, it is not advisable to seal the wall to the pipe as due to thermal expansion, this would then crack so you must leave a minimum clearance all the way around that pipe of 1.5 times its own diameter (125mm diameter pipe requires 187.5mm space all the way around for example). The hole created for that can then be tidied up with a Rosette Collar

Constantine Kambitsis says:
16th June 2020 at 4:30 pm
I and thinking about putting a woodburning stove into my new house which is currently being built. I would need to pass a twin-wall flue for the stove through a flat roof that covers a single storey section of the house. The structure of the flat roof is wood (combustible!) and the covering is single-ply PVC. I am aware there needs to be an air gap of 60mm from the flue pipe to any combiustibles. I am also aware that I need a vented ceiling piece on the underside of the ceiling. What I am not sure of is whether the hole that passes through the ceiling and the roof need to be vented at the top as well as the bottom? I would ideally like to use a flashing with a silicone ‘sock’ that can be cut to fit snugly around the flue pipe, because if a gap is left around the flue pipe, there is a strong possibility water will find its way in. Please can someone advise me on this matter.

Andrew Shuttleworth says:
17th June 2020 at 9:44 am
Ventilated Ceiling Plates (or Ventilated Fire Stop Plates) are only four use where a flue system is passing through a ceiling, exiting one living space and entering another above. The job of the Venitlated Plate is to release any warm air gathering in the wooden joists and delay the spread of fire/conduction of heat up the flue system and through the home. When passing through a single storey roof, you simply require a Finishing Plate on the underside and a Flashing on the roof surface as long as that safe clearance to combustibles all the way around the twin wall flue is being adhered to.

Anna says:
5th May 2021 at 6:05 am
We’d like a wood burning stove in the bedroom room that’s a loft. It has 7 windows and no doors just staircase leading to downstairs. It has a bathroom too. The previous builder stated it’s not possible to install the stove. Are there any situations where this is true?

Andrew Shuttleworth says:
23rd June 2021 at 3:14 pm
That certainly is a fairly unique set of circumstances to attempt to install a stove into however, I would not say it is necessarily impossible and I would be interested to know on what grounds your installer advised against this. Possibly you would be unable to achieve the minimum 4.5m run of flue required being the installation is in the loft?

James says:
13th July 2021 at 9:18 pm
Hello, I am looking to install a wood burning stove. I would prefer a top exit, but, if we decide to go out of the rear of the stove can you connect straight onto a 45 degree from the rear outlet to a 135 Tee through the wall? Thank you.

Andrew Shuttleworth says:
14th July 2021 at 8:19 am
Exiting a stove through the top outlet with a straight length of stove pipe is the best start you can give your flue system to allow the heat to rise and produce the all important draw. If however, you do decide to use the rear outlet, a 45 degree elbow can be used to take the flue through the wall to meet a 135 Tee Piece outside but ultimately, your HETAS approved installer will be able to calculate the performance of your intended system and will sign off on this design or not.

Sabrina Campbell says:
19th July 2021 at 7:44 pm
I’m looking to extend a pizza oven flue through a corrugated metal roof. Can you advise on the parts I need and the legalities of this. Eg. How high does the flue need to go and what the parts are sealed with.

Andrew Shuttleworth says:
6th October 2021 at 2:14 pm
Ideally, you would want to be using twin wall insulated flue for this system being that it is external but its hard to know how long a flue system would be required to sufficiently power your pizza oven. The twin wall components push fit together and are sealed with a supplied locking band and fire cement or equivelent sealnt can be used to seal the flue system into the collar of the oven.

Nat says:
7th October 2021 at 8:20 am
Hi there, Please can you help me? I want to install a twin wall flue through a static caravan aluminium roof. Using a rubber flashing kit. I understand there needs to be 60mm clearance to combustibles around the flue, so the hole measures 295mm in my case. But the flashing base plate will then be smaller than the hole? Is there a workaround please? Many thanks in advance

Andrew Shuttleworth says:
7th October 2021 at 10:39 am
The 60mm clearance for Shieldmaster Twin Wall flue (50mm for SFL Twin Wall) is a safe distance to combustible materials only (i.e. wood, felt etc). However, should you cut that diameter hole in your roof, you can select a larger Flashing with a larger base size to cover that.

david wilson says:
29th October 2021 at 4:05 pm
I have a firebelly double sided gas stove but have tried numerous cowls but still get alot of wind noise from my bungalow chimney am I able to disuse my chimney and take the liner from the middle of my chimney along the attic and out the gable wall. I previously had a multi fuel stove and had no issues with chimney noise

Andrew Shuttleworth says:
9th November 2021 at 3:08 pm
Even though gas burns at a lower temperature compared to solid fuels, I doubt you would be permitted to run a liner through the attic and out the wall. I would strongly advise consulting a local Gas Safe engineer on this matter!

Bob Horrocks says:
22nd November 2021 at 8:32 am
Hi, i’m going to flue my stove through the existing chimney stack which is mounted half way up the pitched roof but to get the correct height clearance the pipe will need to be at least 3m high – I was hoping to run a single wall pipe from the stack through the existing castellated chimney pot and up and out…. maybe with a support strut if required, can you tell me if it OK to use single wall flue for this – i’ve noticed most people use twin wall when creating a higher chimney flue…? Bob

Andrew Shuttleworth says:
22nd November 2021 at 12:56 pm
You will need to use Twin Wall insulated flue pipes to extend that chimney run and not single skin flue. You can run Helix Flexible Chimney Liner through the existing chimney and then using a Console Plate, adapt from the chimney liner to Twin Wall flue above the stack. For stability, you have a few options; Guy Wire Bracket and Guy Wire Kit, rigid Telescopic Roof Support and/or Structural Locking Bands.

Simon W says:
24th November 2021 at 12:45 am
Hi Andrew, these W&As have been very helpful, so thank you! I’m looking to install a wood burner in the corner of my living room, with the twin wall flue passing through two floors above before going through the ceiling. I am concerned about acoustic and thermal insulation around the flue between floors. How is this insulation typically done? I have 100mm rockwool insulation in all my floors/ceiling, do we cut a snug hole for the flue? Or are there existing products to insulate the flue between floors and prevent sound passing through what would otherwise be a gap around the flue. Cheers!

Andrew Shuttleworth says:
24th November 2021 at 11:45 am
I’m afraid you do need to keep the required clear distance from the edge of the twin wall to any combustible materials (that’s 60mm for Shieldmaster and 50mm for SFL Twin Wall flue). It is then also a legal requirement to install Ventilated Fire Stop Plates on the top side and underside of the floor being passed through to allow the heat to escape from the joists. These Plates neaten the holes cut through the floors but they ensure you do maintain that required spacing around the flue system.

Simon W says:
24th November 2021 at 11:58 am
Hi Andrew, thank you, that’s what I thought re combustible materials nearby. But if there’s nothing combustible within 150mm, can you not insulate with rockwool/an appropriate material right up to the outer skin of the flue? Sure you would not pass building regs for sound transfer with 50/60mm air gap around the flue, ie nothing to stop noise between floors? Cheers

Andrew Shuttleworth says:
25th November 2021 at 4:54 pm
In theory this is safe to do as Rockwool is a non-combustible material but officially, we wouldn’t recommend filling this void at all.

Stuart says:
28th November 2021 at 3:54 pm
Hi, I live in a bungalow, wood burning stove with straight twin wall going through ceiling into loft then out via the roof, it was installed with a ventilated fire stop between living room and loft. The loft is empty apart from insulation between the joists, recently I have been feeling a draft from the loft in to the living room coming from the fire stop, is the fire stop ventilation required in this set up? Thank you

Andrew Shuttleworth says:
29th November 2021 at 10:08 am
A Ventilated Fire Stop Plate is a legal building regulation requirement I’m afraid for that passage through the ceiling into the roof spce. This serves two functions – 1) it allows heat to escape from around the combustible wooden joists and 2) it delays the spread of fire up the flue system itself into the loft and roof.

Ian Cornwall says:
14th December 2021 at 5:20 pm
Hi there Glowing embers people, …. Andrew? …. I don’t know if this is the right place to ask a question … but how do you put a stove pipe (double skinned ??) up through a steel box section roofing on a garage??… and how does the ‘rain proof’ flashing? fit onto a box section sheet to make it water tight?? Any pointers gratefully received, .. Thanks.

Andrew Shuttleworth says:
15th December 2021 at 11:40 am
This would be similiar to passing through any non-tiled roof, you will just need to select the correct Flashing for this; Firstly, you will need to create a space in the roof for the flue to pass through keeping a safe distance around the pipe to any combustible materials of 50mm for SFL Twin Wall or 60mm for Shieldmaster. You can support the pipe in this space with a roof support bracket. Secondly, you will require the Flat Roof Flashings (link below) which are maleable and can be shaped to the contours of the roof type (within reason). This can then be secured down with A Fixing Kit and made water-proof with silicone sealant. Links for these are below also for you. Flashing – Fixing Kit – Silicone –

Simon Hartley says:
6th January 2022 at 9:26 am
Hi, Can you advise if there is kit to pass/seal a flue through a rubber (epdm) roof? Many thanks

Andrew Shuttleworth says:
6th January 2022 at 11:41 am
The items displayed in the link I have attached below, specifically the flashing fixing kit used in conjunction with the master flash flashing (either high or low temperature), should be sufficient to seal around the flue as it passes through the roof. The silicone is used on the underside of the square base which you will then press down and fasten to the roof surface using the fixings provided –

Sean Davey says:
9th January 2022 at 10:39 am
Hi, can a twin lined flue be ran in an existing chimney breast (the upper stack has been removed).

Andrew Shuttleworth says:
10th January 2022 at 12:05 pm
Only if there is access to every single connection between the lengths of flue. It is this building regulation requirement that prevents people from this method of installation, plus the cost is far higher.

Ruth Rye says:
23rd January 2022 at 10:23 am
Morning We have twin wall going through our loft – how close can it be to the joist ? As it is very close – do we need to put a metal plate on the joist ? Thanks

Andrew Shuttleworth says:
24th January 2022 at 10:24 am
We supply two brands of Twin Wall insulated flue; Shieldmaster and SFL. Shieldmaster has a safe distance to combustibles of 60mm and SFL is 50mm – these are the distances you must keep clear between the outer edge of the pipe and your wooden joist.

Nigel Stovin-Bradford says:
8th April 2022 at 6:43 am
Hi I wish to install a woodburner on a gable end wall in my lounge. The gable end wall is first plasterboard and then rendered blocks. I propose 1m vertical 150mm to 45 deg inside then 45 deg to vertical outside with an adaptor to 180mm. What fireproofing must I use to go through the internal plasterboard and blocks?

Andrew Shuttleworth says:
8th April 2022 at 3:56 pm
Twin wall insulated flue pipe must have a clearance to any combustible materials of at least 60mm (6cm) around the pipe. When passing through a wall, you can use a wall sleeve along with finishing plates either side to allow for this clearance and to cover any remaining hole left after passing the pipe through. See links below for examples. Our sales team are more than happy to assist you in providing an estimate for all the flue material necessary and of course answer any technical questions you may have bye email or phone.

dave millen says:
10th May 2022 at 6:01 pm
Hi Andrew, I am going to route a twin wall flue through the ceiling of my bungalow into a loft space. I intended to copy the set up of our old bungalow .This had a solid plate with heat shield screwed to the underside of the ceiling joists at ceiling level , and a second plate with a heat shield which slots inside the other one, screwed to the top of the ceiling joists. The twin wall passed inside the heat shields and was secure by a support collar attached to the top plate. The plates also had lugs to indicate the safe distance to the joists . This seems a very sensible method. Having read most of your replies to similar queries I think this might not be the correct way. Do I now install a ventilated plate top and bottom of the joists and no heat shield? Thanks.

Andrew Shuttleworth says:
11th May 2022 at 7:06 am
Hi Dave, yes you should really be using Ventilated Fire Stop Plates there rather than the Solid Fire Stop Plates which are intended for gas systems only. The ventilated Plates allow cool air to pass between the floors, keeping the temp of the outer skin of twin wall as low as possible but more importantly, they allow any heat that builds up within those joists to escape and not transfer into the fabric of the home which would be a fire hazard. As the name suggests, they are also then tested to delay the spread of fire up through the home (worst case scenario, obviously). People do tend to prefer the look of a solid plate but building regulations and health and safety advice dictates these must be ventilated. Hope that helps.

kerry says:
27th June 2022 at 7:37 am
Hi I have had defra approved burner fitted on a gable end installer has used no plates. We have now hot water coming in through cement where flue exits wall plus water coming in through air intake pipe this is rain water as fire not being used. The pipe outside has mounds of cement. Should plates have been used especially externally

Andrew Shuttleworth says:
30th June 2022 at 10:05 am
We strongly advise the use of Finishing Plates both on the inside and the outside when passing through a wall, then to bead around the pipe passing through the plate with Envirograf High Temperature Silicone Sealant as this is waterproof therefore adding even more protection to the seal. Has the cement started to crack or move away from the flue pipe? As a temporary fix you could use the sealant but we would advise chipping back the cement and finishing the installation correctly with finishing plates.

Jakki stewart says:
1st September 2022 at 6:26 pm
Hi, we have a two story slate roofed house with a single story lean-to attached. If we put a stove in the lean to, vertical flue going through slates, how far up the wall of the main house must the flue go?

Andrew Shuttleworth says:
6th September 2022 at 8:46 am
This would depend entirely on how close the flue is going to sit externally to the main house. If the flue system is within 2.3 metres from the main house you would need to go up the full height of the house and then above the guttering/apex by a minimum of 1 metre.

Phillip says:
23rd September 2022 at 1:50 pm
I have a wood burning stove that I wish to fit externally to an existing chimney. I intend to put a flex liner in the chimney and then come through the chimney breast and then join to the wood burner via a single wall flue pipe. could you give me some advice on how to carry out the connect between the flex and the single wall.

Andrew Shuttleworth says:
25th September 2022 at 2:56 pm
This is the only occassion you are legally permitted to run single skin stove pipe through a surface; when passing through a chimney breast. To make that connection, you simply require our single to flex adapters (either push-fit or screw-fit). The male underside will slot inside your stove pipe below and requires sealing with fire sealant and the liner slots between the twin skins on top of the adapter, held in place with self-tapping screws

m owens says:
28th September 2022 at 9:07 am
good morning, i live in a new build property so no chimney. my question is, would the standard size twin wall tee 135 or 145 degree pass all the way through the cavity ie external 1 skin brick 100m cavity and standard breeze block so know joints in the cavity? TIA

Andrew Shuttleworth says:
11th October 2022 at 3:33 pm
When passing through an external wall at a 45° angle, you will need a 45° Adjustable Wall Sleeve, and fixed or adjustable length of Twin Wall pipe. Allowing for clearances to combustibles, and for the distance from the back of the stove to the wall the flue will be passing through, you can work out the horizontal distance needed (thickness of wall and amount of pipe inside and outside the wall) using the following: (Distance from start of offset to wall + thickness of wall + distance to end of offset) x 1.414 = Length of pipe needed. Example: (50mm+300mm+50mm) x 1.414 = 565.36mm

bruno says:
2nd October 2022 at 12:44 pm
Hi I am looking to get a wood burner stove. I currently have a chimney breast that stops at ceiling level. Can I run double skin liner from the stove inside the chimney then connect it outside to a rigid double skin flue up to Ridge height On the gable end. I presume I would have to cut a hole from the outside of chimney to then connect it at 45” to a connector plate and then 135” rigid to roof level. Thanks for any help or suggestions.

Andrew Shuttleworth says:
11th October 2022 at 3:32 pm
Thank you for your enquiry, yes this is correct however you would need to convert from the flexible liner to the Twinwall with a product called a Console Plate with Adaptor. Then as you mentioned travel through the wall diagonally at a 45° angle with the 135° tee piece on the outside. If you are travelling up some height I would also advise you purchase the Adjustable Base Support. If you can put together a rough sketch of the planned flue system you can email this to the team on [email protected] and we can send back a full quote and list of products.

Allan says:
11th October 2022 at 5:14 pm
I have a 2 storey house built in 2007. It has a brick outer wall, cavity wall insulation ‘bats’ with aluminium facing one side and ‘dry lining’ plasterboard internal walls. I believe I understand the requirements from the stove to outside for a lounge installation but it’s when I come to the facia/soffit/gutter line I have a question. The soffit is about 12? wide placing the facia outside this and the gutter outer edge another 4? further out from the house wall (total from wall to outer of gutter 18? approx.). To clear this I estimate a 20? extra ‘stand off’ would be required, not very elegant/mechanically sound. Also, I’m 300ft up a hill 1/2 mile from the North Wales coast and it can get quite windy/gusty. Is it possible to pass through the soffit (if so, parts required) inboard of the facia on which the gutter is mounted and then pass through the lower line of tiles on the roof using a suitable flashing plate? Thanks

Andrew Shuttleworth says:
20th October 2022 at 3:35 pm
You can do your installation this way, you would already be in the correct Twinwall flue. If you would be happy to send across a rough sketch to [email protected] and including dimension detains we could certainly provide you with a full quote for the entire system?

Ian says:
14th October 2022 at 6:24 am
I’m looking to install a stove into a bungalow type wood framed house that has vinyl siding on the external wall and a corrugated metal roof. Although I could go straight up through the ceiling and then the metal roof, I’d prefer to go through the wall using a 45 bend inside and a 135 outside, then straight up for the rest. However the external vinyl siding makes me nervous even when using a double wall flue & wall sleeve and keeping to recommended distances from combustibles. I dislike the idea of cutting a hole in the corrugated metal roof for the flue, which is why I’d prefer to go through the wall. Are there any issues with vinyl wall siding that mean I should just forget about going through it and go through the roof instead.

Andrew Shuttleworth says:
20th October 2022 at 3:34 pm
As long as you stick to the stated distance to combustibles you would be fine. Please note that all Twinwall brands will have a different specified distance, for example our SFL is 50mm and our Shieldmaster is 60mm.

Bill Clark says:
14th October 2022 at 4:56 pm
I am planning a Wood burning stove installation with an external flue. On this external wall my roof soffit and gutter overhangs 400mm. I order to reduce the number of bends and keep my Flur running vertical is it acceptable to pass it through the soffit and use a dectite fitted into my roof concrete tiling. On the soffit underside would a sealing plate ensuring 60mm clearance be sufficent>

Andrew Shuttleworth says:
15th October 2022 at 10:37 am
I would urge you seek the advice of the HETAS registered installer who will perform the installation to find out what they advise or are happy to do/sign off but in theory yes, you are able to pass straight through those soffits ensuring distances to combustibles are adhered to.

Josh says:
3rd November 2022 at 12:39 am
How would you finish the outside hole once the twin wall pipe had come through to prevent water entering as the stones on the house are uneven so finishing plates wouldn’t sit flat to the wall ? Can I just use fire cement around the flue to fill the cavity and give a neat finish ?

Andrew Shuttleworth says:
3rd November 2022 at 4:34 pm
I wouldn’t advise cement around the pipe as this would not allow breathing space for the pipe and can cause wall damage. Instead I would suggest that you render and smooth the surface of the wall with fire cement and then use the finishing plate on the smooth surface.

Rich Brown says:
11th November 2022 at 8:10 pm
Hi I am putting a twinwall flue through a fibre slate roof. Rafters are greater than 60mm from flue. I have an aluminium cone flashing to fit. I am happy slating around this. However not sure what to do about 1) Roofshield membrane! Do I need to cut a whole in it 60mm around flue pipe. (Seems like a gaping hole for potential leaks elsewhere in the roof!) 2) the 60mm gap around the pipe is it to be left empty within rafter space, or can rockwool be used as insulation safely. Many thanks in advance for your advice. Cheers Rich

Andrew Shuttleworth says:
17th November 2022 at 8:47 am
The 60mm clearance for Shieldmaster Twin Wall flue (50mm for SFL Twin Wall) is the minimum safe distance to combustible materials only (wooden rafters, felt etc). With this larger hole in the roof, you can simply select a larger flashing to cover that hole to prevent any potential of leaks. Don’t forget to incorporate the storm collar over the flashing to protect the seal and a finishing plate, to whichever degree, on the underside of the roof.

Frances says:
14th November 2022 at 4:33 pm
hi is it possible to fit a 45 degree elbow directly to the top of a log burner before it goes through the wall?

Andrew Shuttleworth says:
15th November 2022 at 3:12 pm
Yes you can, however you could potentially experience some draw issues. The most successful draws will have at least a 500mm/600mm vertical section of flue before introducing an elbow.

John Barton says:
20th November 2022 at 5:53 pm
Hi there, I am wanting to install a wood burner more or less centrally in an a room with an open vaulted ceiling measuring approx 3m from the top of the stove to the inside of the intended exit point. I note that when flue is mounted adjacent to a wall there is an expectation of wall brackets every 2.5metres. What would you suggest I do in this situation to result in a compliant installation? Many thanks john

Andrew Shuttleworth says:
9th December 2022 at 4:20 pm
We would advise consulting with a Hetas registered installer to seek advice. They would be able to do a site survey and advise on how best to support the flue. Having brackets that extend that far in to the room wouldn’t be suitable, so I would imagine it would be supported as it passes through the ceiling.

Stevie says:
27th December 2022 at 10:37 am
My twin wall flue will pass through the floor and will come through to the hall. Is it possible to avoid boxing it in? or is it required? we like the look of the flue and would like to keep it exposed.

Andrew Shuttleworth says:
30th December 2022 at 1:10 pm
It isn’t a building regulation requirement, most people box this in for aesthetic reasons but all connections must be accessible. Boxing in also offers a level of safety to prevent people touching, or anything coming into contact with, the hot flue pipes.