Category Archives: Flues

Flues, Stove Installation

How to install a wood stove chimney through a wall (Non-chimney installs)

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1) Start your insulated system with a length of single wall vitreous enamelled pipe.
2) Convert to twin wall flue pipe using a Converter from Single Wall Adaptor.
3) To build your insulated flue pipe system, you have to plan your route and measure out what components, pipe lengths and bends you will need.
4) To go through a wall, you will need a wall sleeve to protect the wall and a finishing plate to cover the hole, which must be larger than the outer diameter of the pipe.
5) If you decide to continue internally, then you can pass through a ceiling using a firestop plate.
6) Pass your insulated pipe through the roof again be sure that no part of the roof touches the pipe.
7) Finish off with a chimney cowl or rain cap.

Twin Wall Flue Installations

If you do not have an existing chimney in your home and you want to install a wood burning stove, or if you want to install a free standing modern wood burning stove, you will need to use Twin Wall, Insulated Flue Pipe. We have a complete range of Double Wall Flue pipe from Shield Master, Convessa and Dinak DW along with three brands of accompanying single wall enamelled stove pipe.

 

No Two Twin Wall Flue Installations are the same

Because no two installations of twin wall flue pipe are exactly the same we cannot supply kits, as we can with the flexible flue liner kits. You have to decide where you want the flue to run through the house. You need to either go through a wall and then out and all the way up an external wall to above your roof or you need to go up internally, through your floors and through the roof itself. The path the flue will take to do this will depend upon the configuration of your home and how you want to route the flue pipe.

Accordingly you will have to plan and measure out your twin wall flue system. If you do not feel comfortable doing this then you can get in touch with a local builder or HETAS installer, who will be able to help you. Either way you should make yourself familiar with the building regulations as wood burning stoves do fall under these regulations – more information can be found here. This page is designed to help you understand how to put your system together and take some of the mystery out of planning an installation – however, it is not a complete guide. If you would prefer, telephone us to discuss your installation with one of our team before committing yourself to anything.

 

1) How to start your insulated flue system

You should start your system with a length of single wall vitreous enamelled pipe as this is both cheaper and harder wearing, so is more suitable for use with the high temperatures experienced directly from the stove. However for asthetic purposes etc, you can begin your run by using the adaptor to twin wall and cementing this directly into your stoves’ flue collar.

If you start your run with single wall pipe you can run internally with this but you cannot pass through walls, ceilings or roofs with it and it can only be used internally. If you have a larger internal wall to scale before going through any obstacles then by all mean use the Enameled Stove Pipe all the way up internally, as this is more economical. You must just convert to twin wall pipe at least 4 inches before passing through a wall, ceiling or roof.

2) Converting from Single Wall Stove Pipe to Twin Walled Flue Pipe

Before passing through a wall, ceiling or roof, you will need to convert to twin wall flue pipe using a Converter from Single Wall Adaptor, found here. This slides into the top of your single walled pipe and allows twin walled flue pipe to be attached to the other end. This plus all other joins between pipes in a twin wall flue system require a locking band to seal the join, which is included free with our Shield Master and Convessa range of pipe but must be purchased seperately in the Dinak range. Alternatively some of our wall brackets include a locking band, so you can strategically place your wall mounts at the joins of the pipe to save on components.

3) Building your Insulated Flue Pipe System

Now you have converted to Twin Walled Flue Pipe you just have to plan your route and measure out what components, pipe lengths and bends you will need.

4) Passing your twin wall flue pipe through a wall

If you decide to go through a wall, you will need a wall sleeve to protect the wall and a finishing plate to cover the hole, which must be larger than the outer diameter of the pipe to avoid it touching the wall. These two components allow your twin wall pipe to safely pass through a wall. Once outside you can just attach a 45 degree elbow and continue directly up the external wall.

5) Passing your double wall pipe through a ceiling

If you decide to continue internally, then you can pass through a ceiling using a firestop plate, which ensures that you cut back the ceiling far enough away from the pipe and covers and finishes the holes. Please note: you must use a ventillated firestop plate for wood burning stove installations, the plain firestop plates are for gas installations only. You need to use one either side of your floor (i.e. one on the ceiling and one on the floor above).

6) Passing your insulated pipe through a roof

To pass through a roof again be sure that no part of the roof touches the pipe. Use a firestop plate on the underside of the roof to cover the hole and flashing on the top of the roof to seal it. You will need the high temperature flashing if your insulated pipe passes through the roof less then 5 meters away from your stove, otherwise the low temperature flashing should be fine. If you have a corrugated or uneven roof you will need the EPDM masterflash which molds to the shape of your roof. A fixing kit is available for the flashing which gives you everything you need to create a weather proof seal.

You will need a storm collar to clamp the top of the flashing tight around the twin wall flue pipe to create a weather proof seal.

7) Insulated flue pipe chimney cowls

You need to ensure that your twin wall flue pipe is at least 600mm higher than the pitch of your roof or the top of your flue pipe should be at least 2.3m horizontally away from the roof as it slopes away, whichever comes first. On top of your pipe you will want to finish off with a chimney cowl or rain cap, available here.

Flues, Stove Installation

Chimney installations

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ABOVE: Lining a chimney using a multi fuel flexible liner for wood burning stoves.
 
Reasons for lining a chimney when installing wood burning stoves
 
For a wood burning stove to work correctly it must be connected to a sound chimney and correctly sized flue, therefore it is always recommended fitting a chimney liner when installing a new multi-fuel stove.

If a chimney liner is not installed there are a number of problems that you may experience.

1. Smoke and fumes from wood burning stoves leaking into other rooms or parts of the building.

2. Tar seeping through the chimney walls causing staining.

3. The old flue surface has deteriorated, resulting in poor up-draught.

4. The flue is much too large for the type of appliance being used resulting in poor up-draught.

5. The flue is cold and damp especially if it’s on the outside wall, reducing the heat of the smoke and gases resulting in poor up-draught.

 

Can I do the work myself?

Although lining a chimney for wood burning stoves now falls under building control it’s not a complicated job and can be done by a competent DIYer, however you must inform your local building control department who will inspect the work once the job has been completed. Please click here for Building Regulations that apply to stoves. Document J

If you would like your chimney liner to be installed for you, please see our HETAS installer page.

Tools required to install a flexible chimney liner

There are no specialist tools needed to fit a flexible chimney liner for wood burning stoves, however you will need access to the top of the chimney stack using roof ladders or preferably scaffolding, it is highly recommended to use harnesses when working at height, other safety equipment should include masks, goggles and gloves.

Installing the flexible flue line

1. Before you start the chimney must be swept and inspected for structural defects and the area around the stove should be protected from debris and dust.

2. If you are using our chimney pot hanging cowl, you can skip this step, otherwise you will need to remove the chimney pot and mortar on top of the chimney stack.

3. Cut the register plate to size and fix the angle iron in place.

4. You will need a piece of rope 5 meters longer than the liner. Tie a weight to it and lower it down the chimney.

5. Attach the nose cone to the bottom of the liner (the liner is directional, arrows pointing upwards) and if using Rockwool, Chimwrap or k-wrap secure this to the liner.

6. Tie the rope to the nose cone and lower the liner down the chimney, if there are bends in the chimney and the liner gets stuck it is possible to open up the chimney from inside the house to help the liner navigate the bend.

7. Once the chimney liner is in place, connect the chimney liner to the appropriate adaptor using stainless steel self-tapping screws then fit the stove pipe, now fit the register plate, put the stove in place and seal around the register plate and flue pipe with fire cement.

8. If you have pre insulated the flexible flue liner it is recommended that you put adequate vermiculite insulation above the register plate to stop the heat escaping in to the chimney void, this should be done before putting the top plate on.

9. If you haven’t pre insulated the flexible flue liner then it is recommended you fill the chimney void with vermiculite insulation.

10. If you are using a chimney pot hanging cowl cut the flexible flue liner to length and attach the chimney pot hanging cowl to the chimney liner using the provided fixing straps, insert the cowl into the chimney pot and attach using the straps provided.

11. If you are using the traditional method cut the liner to length and fit the top plate and insert and then the top clamp.

12. Re-fit the chimney pot and leave for 34 hours before performing a smoke test.

Wood burning stoves should always be treated with care, regularly maintained and well installed. A poorly installed or poorly cared for wood burning stove can cost lives. These instructions are designed as a guide only to help safe installation but if you are unsure on how to install your wood burning stove then please do contact a professional.

Building Regulations, Flues, Wood Burning Stoves

Distance To Combustibles

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Due to the high levels of heat emitted from flue pipes and stoves it is essential these are installed at a safe distance from any combustible material. The clearances required vary from Single to Twin Wall flue and are controlled by building regulations and despite some seeing them as a nuisance to their installation, they are designed to keep you safe and protect the construction of your property. For stoves, the safe distance is determined by the manufacturer and recorded on the data plate.

As these have no insulating material, Single skin pipes lose a lot of their heat and become very hot on the outer surface. It stands to reason that to be safe you must maintain quite a substantial distance between these and combustible materials. Building Regulations state this clearance must be at least 3 x the diameter of the flue pipe as illustrated below. If the surface is constructed from a non-combustible material or you have shielded it with fire proof boarding such as our Vermiculite Boards, then this distance can be reduced to 1.5 x the diameter of the flue pipe.

SW Distance to Combustibles

Due to the 30mm layer of compressed Rockwool insulation within these pipes, the heat emitted from a Twin Wall flue is greatly reduced and so is the safe clearance to combustibles. For our Convesa Twin Wall, this distance must be at least 60mm. This figure is included within the designation number applicable to your brand of Twin Wall pipes. There is no regulation for the distance of Twin Wall flue pipes to a non-combustible material.

  • STOVES

Stoves require the greatest clearance to any potentially combustible material but this does come down to the individual brand and model of appliance and is stated on the data plate. This measurement could be in the region of 600mm, 800mm or even greater and may be different for the sides and rear. There is no regulation for the distance of a stove to a non-combustible material, only clearances recommended by the manufacturer (usually in the region of 100mm to allow air to pass around the appliance).

Data Plate

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Building Regulations, Flues

Flue Diameters

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The diameter of flue pipe required for your system will initially be dictated by the size of the flue outlet on your particular stove. From this point onwards the Building Regulations are very clear on the size you must be in for the remainder of your flue installation.

The most common regulation that the majority of flue systems in the UK must adhere to is:

“Closed appliances of up to 30kW rated output burning any fuel 150mm diameter or square flues having the same cross sectional area”

This clearly states that you are required to install a minimum flue diameter of 6” (150mm) and this is the case whether you are using Twin Wall insulated flue pipes or Flexible Flue Liner. But what if the outlet on your stove is smaller than this? Not to worry, this is quite often the case and you are simply required to use increasing adaptors to attain the 6” diameter by the time you convert to your Twin Wall or Flexible Liner.

DEFRA Image

The ONLY exception to the rule above concerns DEFRA Approved stoves most commonly installed in designated Smokeless Zones. The regulations for these models are as follows:

”Closed appliances of up to 20kW output which: a) burns smokeless fuels or b) is an appliance which meets the requirements of the Clean Air Act 125mm diameter or square flues having the same cross sectional area”

This permits a minimum flue diameter for a DEFRA stove of 5” (125mm) and does not require the increase to 6”. Please click here for our full range of DEFRA Approved stoves.

Below are a few basic rules for your flue pipes:

    • The diameter of your stove outlet is the minimum diameter your flue system can be
    • In no circumstance should you ever reduce the diameter of your flue system
    • The diameters quoted in the Building Regulations are minimum diameters only
    • If your stove outlet is greater than 6” then your flue system is going to be greater than 6”
    • DEFRA stoves burn cleaner and / or burn smokeless fuels which leave less soot and tar deposits hence the reduced diameter flue required
    • Some registered installers won’t even attempt to fit anything less than a 6” diameter flue

 

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Building Regulations, Flues

Flue Heights

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As one of the purposes of your flue system is to remove flue gases and the products of combustion, it stands to reason that your installation must be of a certain length and height to safely distribute these fumes away from your home and up into the atmosphere, not your neighbour’s upstairs window. Building Regulations recommend a flue system of at least 4.5m in length to achieve this.

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.

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 own illustrations below will help out.

Flue Height 1

Flue Height 2

The only situations where these distances change are if there are obstacles in the vicinity such as windows in the roof or buildings extremely close by. This needs 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, 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.

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 but your height above the ridge must increase to at least 2300mm:

Thatched Roof Regulations

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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