Heating and Ventilating

With a degree of confusion as to the correct product designation under BS EN 1856-1 for system chimneys, Jason Lee, technical sales manager of SFL, explains the key requirements
IT is well over a year since the introduction of the Harmonised European Standards under the Construction Products Directive (CPD) governing the requirements for metal chimney products.

With the introduction of BS EN 1856-1: Requirements for Metal Chimneys: Part 1 - System chimney products, a dramatic move was made away from the traditional approach adopted in previous British Standards. These previous Standards tended to be more fuel specific, eg BS 4543: Part 1 & 2 governing factory made insulated chimneys with stainless steel flue linings for oil and solid fuel appliances, BS 715 – Specification for metal flue pipes for gas fired appliance and so on.

With the introduction of BS EN 1856-1:2003 and BS EN 1443:2003, the UK market was introduced to the European chimney designation system, which facilitates the performance classification of the chimney product. This new system utilises a set of performance classes for the chimney product and includes Temperature Class, Pressure Class, Condense Resistance, Corrosion Resistance, Liner Specification and Sootfire Resistance.

However, there remains a degree of confusion as to the required chimney designation for solid multi-fuel applications for system chimneys. The performance classes for product CE Marked to BS EN 1856-1 are as detailed below:-



Temperature Class (T80, 100, 120, 140, 160, 200, 250, 300, 400, 450, 600)

Although it is accepted in Europe that a T400 designation is acceptable for solid fuel, the UK has historically under BS 4543, undertaken two thermal product tests, one at 540°C and a further at 760°C. For this reason a temperature class of T450, which means that the thermal tests are undertaken at 550°C and not 500°C as required for the T400 class, is claimed by the leading British manufacturer. It holds the view a T450 rating is more reflective of the potential flue gas temperature for multi-fuel appliances and is in keeping with the 550°C thermal test temperature historically used in the UK under BS 4543.

Pressure Class (N1, N2, P1, P2, H1, H2)

The Pressure Class relates to the product’s suitability and gas tightness when used on positive (P) or negative (N) draught applications and is further classified as to the degree of leakage allowed with either a 1 or 2, with 1 having the tightest leakage rate. For most solid fuel applications where the chimney operates under negative draught conditions, an N1 designation would be common. The N1 designation requires the chimney to meet a leakage rate of less than 2.0 l.s-1.m-2 at a test pressure of 40Pa over the surface area of the chimney system.

Condense Resistance (W, D)

This is either classified as W (Wet) or D (Dry) and determines the product’s ability to contain condensate within the chimney. Typically a chimney serving a condensing appliance would require a (W) classification, as the flue gas temperature would be below the water dew point. Traditionally, chimneys serving solid fuel would tend to operate at a high enough temperature to avoid condensate, therefore requiring a Dry (D) classification.

Corrosions Resistance (V1, V2, V3, Vm Lxxxxx)

This classification relates to the durability of the chimney liner against corrosion and offers three classes (V1, V2 & V3), as well as allowing the manufacturer to self-declare (Vm) the corrosion resistance based on historical experience and data. Also covered is the chimney liner material specification which details material grade and liner thickness. The classes directly relate to three corrosion tests depending on the type of fuel being used. These are as follows:-

•V1 Gas: Sulphur content <= 50mg/m3, natural gas L + H Kerosene: Sulphur content <= 50mg/m3

• V2 Gas: Natural gas L + H Oil: Sulphur content <=0.2 mass % Kerosene: Sulphur content >= 50mg/m3 Wood in open fireplaces

•V3 Gas: Natural gas L + H Oil: Sulphur content > 0.2 mass % Kerosene: Sulphur content >= 50mg/m3 Wood in open fireplaces Wood in closed stoves Coal Peat

•Vm Self declared by the manufacture as suitable for the application based on product history and historical performance in the field. The corrosion resistance class should be matched against the fuel type or it can be self declared by the chimney product manufacturer.

The liner specification offers a number of material codes together with the liner thickness. So a typical liner for multi-fuel application would be L50040, indicating a grade 316L stainless steel liner of 0.4mm thickness.

Sootfire Resistance (G[X] O[X])

This is expressed as either ‘G’, with sootfire resistance or ‘O’, without sootfire resistance, followed by the product’s declared minimum distance to combustible material expressed in mm.

To obtain the G classification, the product has to be tested at 1000°C for 30 minutes and remain intact, while the temperature of the combustible material at the designated distance does not exceed 100°C at an ambient of 20°C.

For solid fuel applications, the chimney system must be sootfire resistant and have a G(X) designation. The distance to combustible (X) will vary depending on individual manufacturer’s products, however a typical classification for multi-fuel applications would be G(50).

Putting all the above performance classes together would equate to a product designation, for example using the SFL SM250 product name as reference, which would look like:- SM250 BS EN 1856-1 T450 N1 D Vm L50040 G(50).

BS EN 1856 also introduces a requirement for a certified factory production control system which is in addition to any existing ISO 9000 factory quality scheme. This ensures, through continuous assessment and external quality audits, that the manufactured product conforms with the performance designation of the product.

Chimney products manufactured, tested and approved to BS EN 1856, are entitled to carry the CE mark. This differs fundamentally from the previous BS standards as the factory production control certificate is a required part of BS EN 1856. Therefore, if the product is not CE marked, then it does NOT conform to BS EN 1856.