Abstract: A heat exchanger comprising a number of interchangeable, possibly standardized sections. Each section is made in the form of a bundle of at least partly longitudinally finned tubes, and has strips which serve as spacer elements for fixing the tubes at a certain distance from one another, and bands embracing the tube bundles. The strips have alternating one-sided projections, each projection having the shape of half the perimeter of a rectilineal polygon. Each pair of strips forms cells. The tubes have non-finned portions along the widths of the strips these portions being located at the same level for all the tubes in a section. The cells embrace the non-finned portions of the tubes so that the latter are arranged in parallel rows.