The minimum requirements for permanent ventilation for certain appliances depend on knowledge of the air tightness of the dwelling where they are to be installed. Dwellings built after 2008 are likely to have evidence of the air tightness either through an individual air permeability test certificate or through representative testing of the same design of dwelling on the same housing development.
The designation of a chimney consists of:
Diagram HJ23 - Chimney designation - Extract from TGD J
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 class
Temperature classes are set out in the table A1 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 HJ15 - Temperature classes - Extract from TGD J
Pressure classes
Pressure classes are set out in Table A2 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 while the number relates to the gas tightness of the product. A1 designation being more gas tight than A2. This allows for different class of products, e.g. metal chimneys to I.S. EN 1856-1 have the class N1 while N2 would be normally assigned as a minimum to masonry chimneys. P and H relate to chimneys which operate under positive, e.g. for fan assisted
applications and diesel generators respectively. The pressure designation depends on the gas tightness it achieves, the lower number being more onerous, the higher allowed leakage for positive pressure application being intended to external installations.
Table HJ16 - Pressure classes - Extract from TGD J
Condensate resistance class
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 temperature high enough to avoid condensate formation.
Corrosion resistance classes
Corrosion resistance classes are set out in Table A3 – this is fuel dependant and expressed as 1, 2 or 3.
Table HJ17 - Corrosion resistance classes (from I.S. EN 1443) - Extract from TGD J
Sootfire resistance class
Sootfire resistance class – expressed as either ‘G’ with sootfire resistance, or ‘O’ without. A product assigned the designation ‘G’ has been tested at 1,000° C for 30 minutes.
Distance to combustible material
The designation of the minimum distance from the outer surface of the chimney to combustible material is given as xx expressed in millimeters (e.g. the distance ‘x-x’ identified in sub-section 2.5.8 and Diagram 7).
Standards for chimneys
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 a designation Liner – I.S. 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 300 mm. Table A5 and A6 gives the correlation between
certain standards and the EN 1443 designations.
The designation of the corrosion resistance class of a metal chimney product is dealt with in I.S. EN 1856-1:2009 and I.S. EN 1856-2:2009 by a two - fold approach. A minimum material specification and thickness is
allowed and 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 0.01 m.
Guidance on the minimum material specification appropriate for the various applications in terms of corrosion resistance (solid fuel, gas and oil) for use in Ireland for products complying with I.S. EN 1856-1 and 2 is given in Table A4. This should be complied with where corrosion tests to V1, V2 or V3 have not been carried out.
Diagram HJ24 - Example of flue designation using material specification - Extract from TGD J
Table HJ18 - Correlation between flue liner material and corrosion load - Extract from TGD J
Table HJ19 - Correlation between designation parameters for clay/ceramic flue liners and flue blocks - Extract from TGD J
Table HJ20 - Correlation between designation parameters for concrete flue liners and concrete flue blocks - Extract from TGD J
