The requirements set out in paragraph 6.2. of this Regulation are considered satisfied in respect of heating systems which include a heat exchanger, the primary circuit of which is passed over by exhaust gases or polluted air, provided that the following conditions are satisfied: the walls of the primary circuit of the heat exchanger must be leak tight at any pressure up to and including 2 bar; the walls of the primary circuit of the heat exchanger must not include any detachable component; the wall of the heat exchanger where the exchange of heat takes place must be at least 2 mm thick if made of non-alloy steels; in cases where other materials are used (including composite or coated materials), the thickness of the wall must be such as to ensure that the heat exchanger has the same service life as in the case referred to in paragraph 4.; if the wall of the heat exchanger where the exchange of heat takes place is enamelled, the wall where such enamel has been applied must be at least 1 mm thick and this enamel must be durable, leak tight and not porous; the pipe conducting the exhaust gases must include a corrosion test zone at least 30 mm long, this zone being situated directly downstream of the heat exchanger, uncovered and easily accessible; the wall of this corrosion test zone must not be thicker than the pipes for the exhaust gases situated inside the heat exchanger and the materials and surface properties of this section must be comparable with those of these pipes; if the heat exchanger forms a single unit with the vehicle exhaust silencer, the external wall of the latter must be regarded as the zone complying with point 5.1 where any corrosion should occur.
5.1 L'épaisseur de la paroi de cette zone témoin de corrosion ne doit pas être supérieure à celle des tuyaux des gaz d'échappement placés à l'intérieur de l'échangeur de chaleur. Les matériaux constituant cette zone et les propriétés de son revêtement doivent être équivalents à ceux de ces tuyaux;