Why and how to install a flexible chimney liner in a fireplace for a wood or fuel burner

Any fuel-burning appliances you have that burn wood/fuel to heat your home must be vented to the outside of your home. This can be done through a chimney liner, which is the material on the inside of the chimney flue that holds the products of combustion from your burner until they are vented out the top of the chimney.

Flexible liners are made from continuous lengths of corrugated pipe that are installed inside the chimney. Cladding a fireplace or installing a wood stove or fire does not mean that the work cannot be done as a DIY job, but all work must nonetheless comply with building regulations. If this work is not carried out by a competent person (for example, a HETAS installer), it should be inspected by someone from the Building Control Department of your local council. This is classed as “Building Site” and you must notify your local council’s building control before work begins. In either case, there may be local planning restrictions to converting chimney work and new chimneys that you need to follow. You may need to erect scaffolding around the fireplace to the ground for health and safety reasons. Reference should be made to ‘The Building Regulations 2000 Approved Document J Combustion Appliances and Fuel Storage Systems 2002 Edition’ or your local council building control department.

A visual inspection of an existing chimney or new flue or chimney installation should be made to verify that it is in good condition, free of obstructions, and is the proper size and type for the appliance you plan to install. If you’re handy with tools and have a good understanding of how chimneys and fireplaces work, you may be able to do most of the cladding work yourself.

The first thing you should do is check your local building and fire safety codes. In some areas, you will be required to have a licensed chimney specialist do the repairs or do new liner installations for you. If you find that you are allowed to do your own chimney work, keep in mind that replacing or installing a chimney liner requires precision work in potentially dangerous conditions. So unless you are sure you know what you are doing, it would be best to let an expert do the chimney repair and liner installation for you. If you’re confused about the best type of liner to install on your chimney, your local chimney cleaning professional can provide advice during your annual chimney cleaning.

Installing a flexible chimney liner on 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 piece of rope (10m), other ropes (for safety), cement, sand, integral waterproofing, unibond, trowel, hammer and cold chisel. , metal snips, buckets, old paintbrush, Phillips screwdriver, adjustable wrench and pliers, roof ladders, ladder or scaffold structure.

Before attempting to put a chimney liner on an existing chimney, you should always chimney sweep the chimney. Do not attempt to lay siding without first chimney sweeping. Remember that debris can fall down the chimney at any time during the flexible liner installation. A wood stove should be installed at the same time, or shortly after installing the flue lining.

Talk to your supplier about the type of wood/oil burner you need and the flue liner you need to serve it. The efficiency of the fire will depend on placing the correct wood stove in the correct opening and using the correct flue. If they don’t all match, you could be wasting a lot of energy.

Installing a flue in an existing chimney can certainly be a DIY job, but some very important rules must be followed. The size of the flue used depends on the size of the wood burner flue outlet. The smoke duct used must not be, in any case, smaller than the smoke outlet of the fire or stove. For a wood burner or other solid fuel fire or stove producing up to 30KW, a 150mm duct should 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 chimney is suggested in all cases. If you open an old fireplace and want to put a wood stove in the opening, you should first arrange to have the fireplace smoke treated to see if it is safe to use without a liner. If your chimney needs lining, check with your supplier about the best lining to use for your circumstances. A flexible liner is the easiest to put on.

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

Now tie a large knot in the end of a rope (preferably 10mm nylon rope) and lower it down the chimney to the hearth at the bottom of the chimney. Tie the other end of the rope to the chimney cap. If you feel the rope you slackened before it touches the hearth, it has probably caught on a ledge or change of direction in the fireplace. Pick up and let go of the rope a couple of times to allow it to fall. When the string is at the bottom, tie a piece of string to the top of the pot or mark it in some other way. The distance between this mark and the knot at the end of the rope is the length of flue you need to purchase. You must also measure the width and length of your stack in order to order a closure plate. The closure plate should overlap the inside edge of the brickwork by about 25mm, leaving 75mm of brickwork exposed all around.

Once you have your lining, you now need to remove the chimney cap and surrounding brace. If this is done carefully you will save the boat. Set the pot in a safe place and flatten the last 9 inches of the liner and fold the flat section back on itself. Push the string through the fold and tie it under the fold. Now use heavy duty tape and tape the folds together. Put a lot of tape on the actual crease of the fold to smooth out any sharp edges. You’ll soon be pulling this liner down the chimney and the more times you get stuck (and we promise you will get stuck!) Now tie a big knot in the other end of the rope and drop it down the chimney one more time. When it reaches the bottom, ask your co-worker to pull it up while you feed it into the hole from the top. When it gets stuck, pull it up a bit and lower it back down. Very few chimneys are straight up and down, so there may be some curves to work with.

Check that the liner is in the correct upward position. There is a purple arrow sprayed on the flexible liner that should point towards the chimney.

Flue liner is not the cheapest material, but don’t be tempted to cut costs by being too precise with the length of liner required. It is much better to have something to cut than to be 25mm short. If you use stone wool insulation, fix it around the flexible lining. You can wrap the entire liner at once or lay it down section by section as you lower it down the chimney. The insulation of your flue is important. It’s a long way from the wood stove to the chimney cap, and as it rises, the hot smoke will cool on the metal cladding. If the liner is not insulated, the hot air could condense and cause a large amount of water to run back through the liner into the stove. This makes the stove or fire totally inefficient. Next, the smoke outlet is placed in the upper part of the wood-burning stove. To prevent heat from escaping through gaps, the flue bracket is placed in a small gap at the top of the wood-burning stove and a piece of fire rope is placed between the two. As the flue is squeezed into the top of the wood stove, the fire rope is squashed into place.

Connect the stove to the flexible chimney liner adapter with a piece of rigid pipe and wait a minimum of 24 hours for it to go out before lighting the stove. A notice plate must be completed and permanently affixed to the building when flues have been installed.