Results of experimental investigations on the influence of turbulence intensity and pressure drop in single rows of plain tubes are presented. The vertically arranged tubes were heated by saturated steam, condensing inside, and cooled outside by air in cross-flow. The turbulence intensity in the entrance cross-section was enhanced by means of different biplanar grids placed in the test section of the wind tunnel upstream before the single rows. The mean streamwise turbulence intensity behind the grids, measured with a constant temperature hot-wire anemometer, varied between 0.8% and 41% Air-side Reynolds numbers ranged from 10⁴ to 4·10⁵. The measurements show for single rows an increase of the Nusselt number for a given turbulence intensity with increasing Reynolds number. The enhancement of the heat transfer, defined as ratio of the Nusselt numbers with and without grid, varies between 42% and 65%. In the investigated range of Reynolds numbers the drag coefficient is only a weak function of the inlet turbulence intensity. The use of turbulence grids thus leads to higher efficiencies of heat exchangers.