Steam condensation heat transfer coefficient (HTC) in a large, flattened tube with variable heat flux, wall temperature and inclination angle is determined experimentally. The condenser tube is that used in air-cooled condensers for power plants. The steel tube has an elongated-slot cross section with inner dimensions of 216 x 16 mm. Vapor and liquid flow concurrently through a 5.7 m long air-cooled conditioning section, and HTC is determined in a 0.12 m long water-cooled test section.. Tube inclination angle is varied from 0 - 25o downwards. The long conditioning section creates conditions in the test section that mimic the conditions in an operating condenser - allowing for realistic development of flow regime and void fraction. HTC is then determined in the water-cooled section. Quality in this section ranges from 0 - 0.75. A visualization section allows determination of flow regime and void fraction. The flow is found to be stratified for all conditions. HTC is found to increase by 6-10 times along the condenser height.