Why and How to Install a Flexible Chimney Liner Up a Chimney For a Wood or Fuel Burner

Fuel burning appliances that you have which burns wood/fuel to heat your house need to be vented to the outside of your home. This can be done through a chimney liner, which is the material on the inside of your chimney’s flue that contains the combustion products from your burner until they are vented out the top of the chimney.

Flexible liners are made of continuous lengths of corrugated tubing which are installed inside the flue. Lining a chimney or fitting a wood burning stove or fire carries no stipulation that the work cannot be done as a DIY job but all work however does have to comply with the building regulations. If this work is not carried out by a competent person (E.G a HETAS installer) it must be inspected by someone from your local council’s Building Control Department. This is classed as “Building work” and you must notify your local council’s building control before work starts. In any case there may well be local planning restrictions converting chimney work and new chimneys that you have to follow. You may be required to erect scaffolding around the chimney down to the ground for health and safety. Reference should be made to ‘The Building Regulations 2000 Approved Document J Combustion Appliances and Fuel Storage Systems 2002 Edition’ or the building control department of your local council.

An existing chimney or a new flue or chimney installation must be given a visual inspection to check that it is in good order, clear of obstructions and is of a suitable size and type for the appliance you plan to install. If you are handy with tools and have a good understanding of how fireplaces and chimneys work, you may be able to do most of the liner work yourself.

The first thing you need to do is check your local building and fire safety codes. In some areas, you will be required to have a licensed chimney specialist make repairs or do new liner installations for you. If you find that it is permissible for you to do your own chimney work, be advised that replacing or installing a chimney liner requires precision work under potentially dangerous conditions. So, unless you are confident you know what you are doing, it might be best to let an expert do your chimney repair and lining installation work for you. If you are confused about the best type of liner to install in your chimney, your local chimney cleaning professional can give you advice during your annual chimney cleaning.

Fitting a flexible chimney liner to an existing chimney is a two person job.

You will need the following tools and equipment to fit a flexible chimney liner to an existing chimney: A length of rope(10m), other ropes (for safety), cement, sand, integral water proofer, unibond, trowel, hammer and cold chisel, metal snips, buckets, old paintbrush, Phillips screwdriver, adjustable spanner and pliers, roof ladders, ladder or scaffolding structure.

Before attempting to fit a chimney liner to an existing chimney, you must always sweep the chimney. Do not attempt to fit a liner without first sweeping the chimney. Remember that debris may very well fall down the chimney at any time during the installation of the flexible liner. A wood burning stove should be fitted at the same time, or soon after a flue liner has been installed.

Talk to your supplier about the type of wood/fuel burner you need and about the flue liner you need to serve it. The efficiency of the fire will depend on putting the right wood burner into the right opening and using the correct flue. If they do not all match up you could be wasting a great deal of energy.

Fitting a flue liner into an existing chimney can certainly be a DIY job but certain, very important rules have to be adhered to. The size of the flue used depends on the size of the flue outlet on the wood burner. The flue used must, under no circumstances, be smaller than the flue outlet of the fire or stove. For a wood burner or other solid fuel fire or stove producing up to 30KW a 150mm flue must be used. For an appliance (burning smokeless fuel only) producing up to 20KW, a 125mm flue can be used. The amount of soot deposit created by a wood burner is quite considerable and a 150mm flue is suggested in every case. If you open up an old fireplace and would like to place a wood burner in the opening you must first arrange for the chimney to be smoke treated to see if it is safe to use without a liner. If the flue needs a liner, check with your supplier as to the best liner to use under your circumstances. A flexible liner is the easiest to fit.

***Please make sure you stay safe while you are working on the roof. Proprietary scaffold and roof ladders must be used and under no circumstances should you attempt this job on your own. It is a two person job.***

Now tie a large knot in the end of a rope (preferably a 10mm nylon rope) and lower it down the chimney to the hearth at the bottom of the fireplace. Tie the other end of the rope to the chimney pot. If you feel the rope you slack before it hits the hearth it has probably got caught on a ledge or a change of direction in the stack. Lift and drop the rope a couple of times to allow it to fall down. When the rope is at the bottom, tie a piece of string to the top at the top of the pot or mark it in some other way. The distance between this mark and the knot that the end of the rope is the length of flue liner you need to buy. You also need to measure how wide and long your stack is so you can order a closing plate. The closing plate should overlap the inside edge of the brickwork by about 25mm leaving 75mm of brickwork exposed all the way round.

Having obtained your liner you need now to remove the chimney pot and the surrounding haunching. If this is done carefully you will save the pot. Place the pot somewhere safe and squash flat the last 9 inches of the liner and fold the flat section back on itself. Push the rope through the fold and tie it together under the fold. Now use some strong duct tape and tape the folds together. Put plenty of tape on the actual crease of the fold itself to smooth of the sharp edges. You will soon be pulling this liner down the chimney and the more times it gets stuck (and we promise it will get stuck!) The more you will wish you had “wasted” a bit more tape rounding off the end. Now tie a large knot in the other end of the rope and once more drop it down the chimney. When it gets to the bottom get your work mate to pull it through while you feed it into the hole from the top. When it gets stuck, pull it up a little and tug it down again. Very few chimney stacks are straight up and down so there may be a few bends to work through.

Check that the liner is the correct way up. There is a purple arrow sprayed onto the flexible liner which should point up the chimney.

Flue liner is not the cheapest of materials but do not be tempted to cut costs by being too accurate with the length of liner required. It is a great deal better to have some to cut off than it is to be 25mm short. If using rockwool insulation then attach this around the flexible liner. You can wrap the entire liner at once or fit it section by section as you pull it down the chimney. It is important to insulation for your flue pipe. It is a long way from the wood burner to the chimney pot and as the hot smoke rises it will cool down on the metal of the liner. If the liner is not insulated the hot air could condense causing a lot of water to run back down the liner into your stove. This makes the stove or fire totally inefficient. Next the flue outlet is fitted to the top of the wood burner. To stop heat escaping from any gaps the flue outlet bracket sits in a slight recess at the top of the wood burner and a length of fire rope is placed in between the two. As the flue outlet is tightened down onto the top of the wood burner, the fire rope is squashed into place.

Connect the stove to the flexible chimney liner adaptor with a length of rigid flue and give it all a minimum of 24 hours to go off before you light the stove. A notice plate must be completed and permanently posted in the building when flues have been installed.