Good Practice TRANSPORT Flue liners and terminals are packed and transported with care. Use mechanical off loading when available. Unload with care. Check their condition and that they are as specified when they arrive on site. STORAGE Store flue liners and terminals on a clean, level area, safe from damage. Retain in their delivered packs as far as possible until needed. FLUE SIZES BS 6461 Part 1 recommends a minimum flue size of 200 mm diameter or 185 mm nominal square for a fireplace recess with an opening up to 500 mm x 550 mm, for an open, solid fuel fire. For larger recesses, the flue requires a free opening of 15% of the area of the recess. The Building Regulations documents specify a range of minimum flue sizes according to the type and rated output of the installed appliance. It should be noted that low output appliances connected to flues sized for greater outputs will be likely to generate acidic condensates. The use of clay liners for these flues will resist this corrosion. RECESS OPENING The fire recess is measured as A x B. HEIGHT In order to obtain an adequate draw to remove flue gases, a flue should be a minimum of 4.5m high from the top of the fire throat unit to the chimney outlet. For stability, H should not exceed 4.5 W. H is measured from the level of the highest point of the intersection of the roof and the outer wall of the chimney and a datum level 0.15 m max.. up the terminal. The top of the terminal may be higher than this datum level. FLUE OUTLETS Flue outlets for flues serving solid fuel appliances should be finished above the shaded areas shown in the diagram below so that the flue gases are carried away from the building. BENDS Ideally, flues should be straight. The use of offsets is not recommended in the Building Regulations documents but, when needed, they can be achieved by the use of bends, typically 22.5°, 30°, 37.5° and 45°. Only one offset is allowed for each flue. The requirements of the Building Regulations documents allow a maximum 45° bend for both gas and solid fuel appliances. The use of different lengths of straight flue between bends allows flexibility in obtaining an offset to avoid any structural obstacle. Only complete factory made liners should be used for both straight lengths and bends so that the joint rebates remain intact. INSTALLATION - FLUE LINERS All liners should be laid with the female rebate uppermost. This ensures that condensates formed from the flue gases are not able to flow out from the flue into the surrounding masonry where they would cause structural deterioration and staining of walls as well as providing a path for the possible escape of dangerous flue gases. The joints between liners must be made with a fireproof mortar or manufacturer's proprietary fireproof sealant. As work progresses, any mortar ingress into the flueway should be wiped clean. This ensures a smooth passage for the flue gases and for sweeping. It can be achieved by using a coring ball, as shown below. This operation should not be delayed until the chimney is finished as the mortar may have hardened and be difficult to remove. The space between the outside of the flue liner and the chimney stack should be filled with insulating material such as a weak lime mortar or lightweight insulating concrete. INSTALLATION - TERMINALS The chimney terminal (or “pot”) is an important component of a chimney system. It takes the flue gas outlet away from the turbulence created by the bulk of the chimney stack and can reduce the likelihood of water ingress. Also, it can put the flue outlet above the high-pressure zone, which causes down draught problems. The terminal should be embedded into the top of the stack by 125 mm or one quarter of the height of the terminal, whichever is the greater. A straight-sided terminal should be butted against the top of the last liner as shown opposite. A tapered terminal should be fitted over the last liner as shown below. Note that the top of the last liner lies within the corralled brickwork in this case. A terminal may be formed by extending the flue liner to project above the top of the stack as shown below. It is recommended that at least 150 mm projects above the flaunching. A flue terminal should always be used to obtain a satisfactory chimney performance. The chimney should not be terminated with just a mortar flaunching. TERMINALS - RANGE A wide range of decorative terminals are available from the members of the Association. TESTING Check new chimneys for blockage and soundness before use. Gently lower a coring ball through the flue to determine that it is free from blockage, as for clearing fresh mortar from the bore. Use a smoke test to check for leakage. Close up any fitted appliance. Warm the chimney flue for about ten minutes using a blowlamp or similar heating device. Put two smoke pellets in the appliance firebox (or bottom of the chimney or the appliance recess) and light. Close the appliance when smoke is formed and allow the smoke to make its way up the chimney. If an open fire is fitted or if the recess is empty, seal the recess using a piece of board sealed at the edges. When smoke is visible from the terminal, seal it, using an inflatable plug or polythene bag. Remember to remove the seal after the test. Check for leakage throughout the length of the chimney by examining the chimney breasts and adjacent walls. Leakage may occur at some distance from a fault. Pay particular attention to barge overhangs and eaves to see leakage through wall cavities.