The evolution of heat generators, increasingly focused on energy saving and environmentally-friendliness, has depleted the temperature of combustion fumes by considerably reducing it and by transferring this energy to the room served by the generator. From an energetic point of view this result has been remarkable and we can see its actualization in many equipments and particularly in high-efficiency boilers such as gas condensing boilers.

The fumes temperature decrease often leads the fumes to produce condensates into the chimney and to have a positive pressure inside the smoke exhaust duct, due to the depletion of the thermodynamic capacity (that sends the fumes up in the atmosphere).



(the picture above schematizes how in the EN 13384/1 calculation method the presence of pressure into the exhaust pipe and of moisture into the chimney are ordinary conditions that are discretized by the solver algorithms)

In the last thirty years the fumes draining systems also developed. In particular, with the application of the European standards, they have been submitted to rigorous production control processes, standardized by the CE marking affixed to the components, the packages, and to their documentation. The producer must inform about the characteristics of the flues, by specifying their performance capabilities such as temperature resistance, pressure, moisture, corrosion, materials employed, thickness, soot fire resistance and distance to combustible materials.

 

Designation	Description
T	Temperature Class (T80-T100-T120-T140-T160-T200-T250-T300-T400-T450-T600)
N-P-H	Pressure Class (N1-N2-P1-P2-H1-H2)
O-G	Soot Fire resistance Class (S-G)
D-W	Condensate Resistance Class (D-W)
V1-V2-V3	Corrosion Resistance Class (V1-V2-V3)
R	Thermal Resistance Class (expressed in m2K/W multiplied by100)
C	Minimum Distance to Combustible Materials (mm)
I-E-B	Location Class (I-E-B)
N-O-C	Flue Casing (N-O-C)
L50	Liner (plate employed to produce stainless steal AISI 316 L/Ti)
0XX	Liner Thickness (plate employed for the production) Expressed in mm/100

 

In relation to the concept of junction between two components and to the related gas tight and condensate tight, we can finally assert to have attained a significant achievement thanks to the recent EN 14241-1 regulation concerning the gasket characteristics (the gasket assures the tightness between two components). From a productive point of view, new kinds of joints have been studied, some of them don't need a gasket anymore but they require however tight pastes for wet conditions.

The gasket guarantees tightness without omitting the clear characteristic of incombustibility of the chimney, as it is its accessory and not its main material

The joint between two components must be mechanical as it must assure the non-disjunction of the components in case of dilatation. For this reason, on the market are available different kinds of joints, from the hose clamp - the most common and used one - to the screw joint, the hook joint, the mechanical interlock joint (by semi-rotation). The common feature is that they all have a mechanical structure that avoid the components disjunction in case of a potential thermal shock. For example, the dilatation of a 6 m flue can be of several centimeters.