Chimney maintenance and inspection

General guidelines from the British Flue and Chimney Manufacturers Association

Checking and relining exisiting chimneys

It is important to check the condition of an old chimney, especially when re-opening one, after many years of not being used. A chimney should contain a sealed flue from the appliance to the chimney pot to transport the products of combustion safely to the atmosphere. Over time the condition of the flue can deteriorate. It was only from 1965 that Building Regulations required all new chimneys to be built with suitable flue liners of the correct flue size to protect the chimney.

The check should be carried out by a chimney specialist and would entail the following procedures:

  • The chimney should be swept to ensure that it is clear obstructions such as dislodged masonry or bird’s nests
  • A smoke test should then be carried out to establish whether there is any major fault that can cause products of combustion to leak through the chimney walls. A smoke test procedure is given later on in this guide.
  • The structural stability should also be checked, as well as making sure the chimney is wind and water tight.

This should identify the repair work that is needed. Often the safest and most economical way to make the flue secure is to reline the chimney shaft with new liners. This can be done with clay, concrete or pumice liners, single wall stainless steel or flexible stainless steel liners.

To reline the chimney with clay, concrete or pumice liners, the liners are lowered down the chimney on guide ropes with locating bands at the joints. The gap between the liners and chimney is then backfilled with a lightweight insulating compound. The existing flue opening has to be made large enough for the liners to be installed. This benefit of this type of re-lining is its durability. However the cost can be prohibitive.

The alternative is to use stainless steel liners, either single wall rigid liners or flexible liners. Stainless steel flexible liners are designed to take on the shape of the chimney. The liners are installed by either lowering them down or pulling them up the chimney. They can go around most bends. Whilst their slim profile enables quick installation into chimneys where other systems might not fit, their life can be reduced if abnormally high corrosive soot or condensate deposits are created and allowed to accumulate in the flue or have not been thoroughly removed from the walls of the existing chimney flue.

Regular inspection

The chimney should be swept regularly to remove soot and tar. At the very least the chimney should be swept at the start of the heating season. It is not recommended that the appliance is over fired, (allowed to burn fiercely and out of control), or chimney fires be started in an attempt to clean the chimney. Deposits of soot and tar will be greatly increased if unseasoned wood is burnt. Should a chimney fire occur, the chimney and appliance should be checked for damage before using them again.

It is also good practise to check at least every year or two the exposed parts of a chimney, flashings and terminals for signs of damage. Just like the outside of a house chimneys can suffer from the wear and tear of extreme weathering.

If at any time smoke or fumes are apparent or suspected from the appliance, chimney or flue, seek advice immediately from the installer or chimney expert in case there is a blockage or failure. Do not use the appliance or chimney until they have been thoroughly checked for safety and soundness. The escape of fumes can be dangerous.

Smoke testing

If there is doubt about the condition of a chimney, or an old chimney is to be put in use after a long period of disuse, it is advisable to have it smoke tested. It is also recommended that a smoke test is carried out during the construction of masonry chimneys and on completion of all chimney installations. A smoke test should be carried out by a qualified person using the following procedure which is based on the test described in the European Standard BSEN 15287-1 for open fires and BSEN 15287-2 for room sealed appliances. There is a different procedure for smoke testing flues for gas fires. It must be remembered that the purpose of the smoke test is to identify any faults which would cause fumes to escape during the normal operation of the appliance and chimney. Closing the bottom and top of the chimney during the test, will generate a positive pressure in the flue. This will force the smoke, generated by the pellet, to escape through gaps in the joints in a masonry chimney, or connections between pre-fabricated metal chimneys and flue pipes.

Minor leakage detected during this test, would not be a major risk when the installation is used during normal operating conditions, providing the point of leakage does not indicate a fault that could get worse. However, if significant or heavy smoke leakage is seen, the cause must be investigated and rectified. Broken components, incorrect fitting and incomplete jointing of flue liners are the most common problems which cause major leakage and require remedial action.

The smoke test involves the following steps:

  • If there is an appliance fitted at the base of the chimney, burn some newspaper in the grate for 2 to 3 minutes to establish a flue draw. A longer warming up time may be needed with wet or cold flues. If there is no grate or fire box fitted use a blow lamp for at least 10 minutes to establish a flue draw. This will assist the testing of the flue and not is intended to simulate real conditions.
  • Place at least two flue testing smoke pellets on a brick in the opening at the base of the flue or in the appliance if it is fitted. Follow the pellet manufacturer’s safety instructions. The actual number of smoke pellets required will be determined by circumstances and the size of the pellets used. Generally, the larger the flue diameter the fewer pellets required. This is the result of the ratio of flue diameter compared to the surface area of the flue.
  • Ignite the pellets and when they start smoking cover the opening with a board or plate sealed at the edges or if an appliance is fitted, close all doors, ash pit cover and vents.
  • When smoke begins rising out of the top of the chimney, cap the top of the flue, terminal or pot using an inflated football bladder or plastic bag sealed in position with tape. A hole with a minimum diameter of 50mm must be left in the capping or sealing device.
  • Examine the full length of the chimney for any leakage of smoke. If possible check for signs of smoke leakage from wall cavities at the sides and back of the chimney, if it is built into a wall. Also check for smoke leakage at openings around windows near to the chimney and the roof space area.
  • If any smoke is seen establish the point of leakage and carry out remedial work to correct any faults.
  • After completing the remedial work repeat the testing procedure until no major leakage or fault is apparent. Remove the closures at the top and bottom of the chimney.


BFCMA (British Flue and Chimney Manufacturers Association) logo-bfcma