Installing a twin wall flue through the roof or wall
You can ONLY use twin wall pipes to pass through a ceiling or wall. This type of pipe is highly insulated, so is designed for this purpose. A single-wall, non-insulated stove pipe will reach an extremely high temperature, so is not safe for passing through a wall or ceiling.
You must also be sure you convert from single wall stove pipe to twin wall flue pipe at least 150mm before passing through a wall or ceiling.
Respect the required distance to combustibles!
When installing a twin wall flue through a ceiling or wall, it’s essential you know the required distance to combustibles. This is vital for preventing hot surfaces from escalating into house fires. For our twin wall pipes the safety distance is 7 cm when in an enclosure and 5 cm when not enclosed.
Installing twin wall flue through the roof
In case you are passing your twin wall flue through the roof, you will need to use a roof support. This gives some support to the system via the rafters.
Once you have placed the twin wall through the roof with the right support in place, you will need to seal it with the appropriate chimney flashing. This prevents rain, snow, hailstones - or any other any type of moisture! - from getting into the gap left between the chimney and roof.
We have a range of different types of chimney flashing to suit all roof styles, whether you have roof tiles, slate or a corrugated surface. You can choose from flexible roof flashing, aluminium flashing or lead flashing
Installing twin wall flue through a wall:
A common way of installing a twin wall flue system is to place it through the wall of the room the stove is installed in. It is then run straight up the side of the house, meaning there are often fewer obstacles to deal with along the way.
When passing a twin wall flue through a wall, you can only use an angle of 45 degrees. You can use a Tee piece of twin wall flue to turn the flue back to vertical easily. Building Regulations also ask that you use a metal sleeve around your flue when passing through the wall. This is to stop the pipe becoming damaged through potential heat expansion.
Remember, you are only allowed a total of four bends in your twin wall flue system - this will use up two of them!
It’s also recommended that you use a base support at the bottom of your flue once you have passed through the exterior wall. These provide good structural security for the rest of your flue system.
For an external twin wall flue system, you should then use an adjustable wall bracket at least every 3 metres.
While not a regulation, it is best practice to allow the first section of pipe that exits the stove to run completely vertical for at least 600mm. This creates the best draw for the chimney. It’s also advised that you use no more than 2m of single wall stove pipe. This is because the stove pipe isn’t insulated, so your flue will be losing more heat than necessary which can lead to poor draft.
Don’t forget, you need to convert your single wall pipe to twin wall pipe at least 150mm before passing through a wall, too. To do this, you will need the right adapter to join them together.