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.