Fitting a flexible liner

Fitting a flexible liner

First, you must determine the appropriate size chimney liner for your specific setup. The chimney liner diameter size you will need is the same as the size of the exhaust hole on the appliance. The chimney liner length you will need will equal the height of the chimney. We recommend ordering slightly over that amount to give room for error.

The flue liner legally needs to be a minimum of 6" in diameter if you are burning wood. Unless when you instal a DEFRA approved stove with a 5" flue outlet, in which case you can use a 5" liner.

If you are installing a liner into an existing chimney, be sure to get the chimney cleaned first as this will ensure there is no residual soot or other obstructions that could create difficulties with the installation.

Once installed, it is important to remember that all such work, that has not been carried out by a HETAS registered installer, must be inspected as per the UK Building Regulations, Document J . This check ensures that all flue liners are properly installed; that they are the right size for the appliance requirements and that they are completely free of obstructions.

Only a few tools are needed for a successful chimney liner installation. You'll need a utility knife, flat head screw driver, caulk gun, a pair of working gloves, a power drill and safety glasses. A grinder will give you the best cut when cutting off the excess chimney liner. A saw or hacksaw will also work fine.

You can install your flexible liner either from the top or bottom of the brick chimney stack. Whichever way you choose to install the liner, please ensure that you have sufficient clearance around the outside of the liner to ensure the least amount of friction, or possibility of catching any bricks within the chimney stack, does not occur.

flue pipeUnpack your flexible liner and attach a rope at the lower end (making sure the rope is long enough to reach the bottom of the stack). Ensure the arrows marked on the liner are facing an upward direction (representing the direction of flue gases). 

You will need two people to install your liner successfully, one at either end of the chimney stack. The person on the roof should be safely attached! From the top of the roof, start to push the liner, down the stack. The person at the bottom of the stack should hold the string and take up the slack. Work in tandem to feed the liner down the chimney stack, ensuring that you leave enough liner at the bottom to secure your adaptor and enough at the top to secure the top fixings.

Once the chimney liner is all the way down the flue to the point of the thimble, the next step is to connect the top plate to the top of the chimney. The main function for a top plate is to seal the existing flue from rain, wind and creatures from entering the chimney. It also has a clamp located on the inside collar of the top plate to support the weight of the liner.  


Start by using your caulk gun and a tube of weather resistant silicone to run a bead of silicone along the top edge of the clay flue.

chimney flue installationNext, thread the chimney liner through the round collar of the top plate so that the top plate is sitting on the top edge of the clay flue.  


Locate the locking bolts welded on the four sides of the top plate. Center the top plate on the clay flue and use your flat head screw driver to secure the top plate to the side of the clay flue.  Warning: Make sure not to overly tighten the locking bolts. If tightened too much the clay chimney flue could crack.

When you have successfully installed the top plate, the next step is to cut the excess liner flush with the top of the collar of the top plate. Shown in the picture is a grinder with a cut off wheel. The grinder will give the best cut, but a saw or hacksaw will work just fine.  

The next step is to secure the rain cap to the top plate. The collar of the top plate will get inserted inside of the rain cap. 

Note: All installations are to be done according to UK Building Regulations, Document J. The tips on this page are meant to help you to do so, but in no way should be considered as a replacement of the instructions and rules of document J.  

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