Appendix G: European chimney designations

G1 This informative appendix provides a summary of the European chimney designation scheme. The essence of the scheme is a series of code letters based on the general chimney designation scheme of BS EN 1443:2003, an example of which and their explanation is given below.


  1. Designation
    1. Temperature classes
      1. Pressure classes
        1. Condensate resistance classes
          1. Corrosion resistance classes
            1. Sootfire resistance classes
              1. Distance to combustible material


                G2 The designation of a chimney consists of:

                Designation of Chimneys

                Designation of Chimneys

                G3 European chimney standards have been developed based on the material of the flue liner e.g. clay/ceramic, concrete, metal, and plastic. Some material based standards have adopted a different shortened designation e.g. for clay flue liners a designation Liner – EN 1457-300-A1-N2 means it is suitable for a chimney with the designation T600 N2 D 3 G, with a nominal size of 300mm.

                G4 The designation of the corrosion resistance class of a metal chimney product is dealt with in BS EN 1856-1 and BS EN 1856-2 by a two-fold approach. A minimum material specification and thickness is allowed which is dependent on that which is permitted in member states regulations, where these exist. Products upon which a declaration has been made in this manner are designated Vm. The alternative approach involves the choice of one of three corrosion resistance tests. Products meeting the tests carry the designation V1, V2 or V3, as appropriate allow the product to be designated with the Corrosion resistance class 1, 2, or 3 respectively. The material specification still forms part of the overall designation, and appears alongside the ‘V’ letter, e.g. Vx-L40045. The material specification for the liner (or connecting pipe) is formed by the letter ‘L’ followed by five digits. The first two digits represent the material type and the last three digits represent the material thickness in multiples of 0.01mm.

                G5 For the UK, guidance on the minimum material specification appropriate for the various applications in terms of corrosion resistance (solid fuel, gas and oil) is given in the UK National Annex to BS EN 1856-1 and -2.

                For further examples of shortened designation refer to the specific product standards.

                G6 In selecting an appliance for a given chimney designation, the appliance, irrespective of the fuel used, is required to generate combustion products with characteristics equal or less than those designated for the chimney. When selecting a chimney suitable for a given appliance, any chimney with performance characteristics equal to or higher than those appropriate for the appliance may be used.

                Temperature classes

                G7 Temperature classes are set out in Table G1 and expressed as ‘T’ followed by a number which is less than or equal to the nominal working temperature, i.e., the average flue gas temperature obtained during the nominal/ rated output test (usually the maximum operating level);

                Table G1 Temperature Classes

                Table G1 Temperature Classes

                Pressure classes

                G8 Pressure classes are set out in Table G2 and expressed as either ‘N’, ‘P’ or ‘H’   followed by either ‘1’ or ‘2’. N relates in general to natural draught chimneys i.e. operating under negative pressure where the value 1 or 2 allows for a different class of product; metal chimneys to BS EN 1856-1 have the class N1. In the UK the value N2 will be assigned as a minimum to masonry chimneys. P and H relate to chimneys which operate under positive pressure e.g. for fan assisted applications and diesel generators respectively. The pressure designation depends on the gas tightness it achieves, the lower number being the more onerous, the higher allowed leakage for positive pressure application being intended to external installations.

                Table G2 Pressure Classes

                Table G2 Pressure Classes

                Condensate resistance classes

                G9 Condensate resistance class – expressed as either ‘W’ for wet or ‘D’ for dry operations. A product designated ‘W’, able to contain condensates within the flue, is aimed at condensing appliances. A product designated ‘D’ would usually have flue gas temperatures high enough to avoid condensate formation.

                Corrosion resistance classes

                G10 Corrosion resistance classes are set out in Table G3 – this is fuel dependant and expressed as 1, 2 or 3.

                Table G3 Corrosion resistance classes

                Table G3 Corrosion resistance classes

                Sootfire resistance classes

                G11 Sootfire resistance class – expressed as either ‘G’ with sootfire resistance, or ‘O’ without, A product assigned the designation ‘G’ has been tested at 1000ºC for 30 minutes.

                Distance to combustible material

                G12 The designation of the minimum distance from the outer surface of the chimney to combustible material is given as xx expressed in millimetres (e.g. the distance ‘x-x’ identified in paragraph 1.45 and diagram 13).