How to install a flue through a wall

Some houses, or rooms in your house, don’t have chimneys whilst you may want a stove in them. At first this may seem like a dead-end, however you can in fact install stoves into houses and rooms without a chimney via a flue built into the walls.

Also known as a twin wall flue, this steel chimney can be fitted through a wall to allow smoke to escape from a stove or fireplace. These flues can either run out of the building and up the outside wall or installed through the walls and out of the roof. The latter is particularly good for some more modern, free-standing stoves which you may want to be placed somewhere else in your room rather than the traditional position of a fire place.

To install a flue through a wall you will first need to plan the route of the flue pipe and decide whether you want it running up the outside wall or through your walls. This is a crucial part of installing the flue as you do not want to be cutting through any central heating or gas pipes or any important electrical wires in your house or have an external flue obscuring any windows higher up in your house.

Furthermore, you will need to plan the route of the flue simply to know which parts you will need to buy to build it and how tall it needs to be. Also make sure that the flue pipes you buy are insulated as uninsulated ones may prevent the heat flowing through the pipes and, hence, the smoke.

Once you have planned the route of the flue and where you want your stove, you will need to make a hole in either your ceiling or wall for the flue to pass through. This is done by measuring the diameter of the flue pipe and cutting out a hole equal to this with a jigsaw. After this is done you will need a wall sleeve to cover the flue as it goes through the wall, protecting it, and a finishing plate to cover the hole which must be larger than the diameter of the flue pipe.

If you are carrying the flue up the outside wall you simply need to keep the flue secured to the wall all the way up to the roof and then fit the top section of the flue with a chimney cowl or rain cap. Remember, your flue must project 600mm above the ridge of your roof.

If you want to carry on through the walls using the ceiling as an entry point, make sure you have a firestop plate to allow the flue to pass through safely. Build the flue pipe through the pre-planned route until you come to the roof. Make an internal hole that fits the flue pipe in the roof and an external one using an angle grinder to cut through the roof tiles. Place a lead roof cowl under the tiles to make sure that no part of the flue pipe touches the roof and build the pipe through this outside.

Once the flue pipe is outside, seal the gap between the tube and the roof with a fireboard which not only fills the gap but also stops the heat of the flue damaging the roof. Secure the flue inside the roof with a rafter support and then fit the top section of the flue with a chimney cowl or rain cap.

Where the flue enters a room from the wall or ceiling in your house you will need to make physical barrier between it and any flammable material nearby. This can be done by build a cage around the entrance or a box out of fireboard. Finally, attached the flue to your stove securely and give it a test run with a small fire made with kindling. A magnetic surface can also be installed to ensure your stove has an efficient, clean burn.