The invention relates to a heat exchanger formed by two tubes of rigid material. The outer tube is open at the top and closed at the bottom, and has a diameter approximately 60% larger than the inner tube and a length greater than 10 metres. The inner tube is also open at the top and closed at the bottom, the perimeter of the lower lateral part thereof comprising a series of holes. The inner tube is inserted into the outer tube and comprises multiple clamps having at least three feet, which are symmetrical and situated in the perpendicular plane of shafts of the tubes and end in respective wheels on free shafts. An air extractor apparatus is situated in the upper part of the inner tube.