PURPOSE: To prevent flowing-in of rain or foreign matter from atmosphere and enable adequate flowing-out of exhaust gas, by a method wherein plural numbers guide vanes, of which side surfaces attached horizontaly to support plates with adequate spaces vertically are inclined towards outside from inside, are provided.

CONSTITUTION: A ceiling plate 32 is provided at the adequate position interposing a support plate 31 above an outlet part 30 of exhaust gas which is positioned at the upper part of anexhaust heat recovering heat exchanger 20. Furthermore, plural numbers of guide vanes 33 are attached horizontally to the support plate 31 at the adequate space between the under surface of the ceiling plate 32 and the upper surface of the exhaust gas outlet part 30. These guide vanes 33 are inclined so as the side surface makes adequate descent incline towards the atmosphere 35 and another contaminants 27 fall through the ceiling plate 32 or directly along each guide vane 33, and finally reach to the ground surface through the exhaust outlet provided at the outer trunk of the exhaust heat recovering heat exchanger 20.