Performance PERFORMANCE - SITE SITUATIONS Leaking flue gases and condensates show up clearly as ugly, permanent stains on chimney walls that can be the indicators of structural deterioration. Clay flues safely contain all combustion products causing no harm to the structure. The acidic nature of flue gases is clearly illustrated by the picture of concrete tiles, which have been severely corroded below a chimney, compared with the replacement concrete tile to the left of the picture. Clay tiles, used above that area, are unaffected. The acid resistance tests provided in the BS EN 1457 for clay flue liners and BS EN 13502 for terminals, provide assurance of the products’ long term performance in service. PERFORMANCE - DURABILITY The increasing use of high efficiency appliances, which give rise to the condensing of flue gases within the flue, give specifiers and installers cause to consider the corrosive effect that the resultant acid condensates can have on certain flue materials. BS EN 1457 and BS EN 13502 provide an accelerated acid resistance test to represent a corrosion resistance and practical installed life of at least 100 years, it simulates the effects of an acid condensate on clay flue liners. The performance requirement for class A1N2 liners and terminals is that the loss in mass of a test sample should not exceed 5%. Certain concrete flue liners suffer a mass loss in excess of 10% when subjected to the same test. In the simple visual comparison test illustrated below, after immersing clay and concrete flue liners in an acidic solution of similar strength to the condensate from a typical modern appliance (pH approximately 3) for less than a week, the concrete demonstrates clear signs of deterioration whilst the clay is unscathed. Further detailed design guidance is available in the Code of practice BS 6461: 1984: Part 1 and the relevant parts of the National Building Regulations documents, as listed earlier. REMEMBER – Clay flue liners and terminals are: •Heat resistant •Acid resistant •Suitable for all domestic fuels •Proven in use for over 50 years (much more for terminals!) •Made to the European Standard