Heat transfer during dehumidification on a vertical copper surface is studied and a correlation was developed to relate the heat transfer coefficient, relative humidity, and surface-to-ambient temperature difference. The heat transfer coefficient at various humidity levels and surface-to-ambient temperature differences were obtained experimentally. Variations of about similar to 200% in heat transfer coefficient were observed between low and high humidity levels. Unlike for pure condensation, it was observed that the heat transfer coefficient is higher for filmwise condensation than for dropwise condensation. It is hypothesized that the non-condensable gas insulates regions where condensation does not take place. (C) 2012 Elsevier Ltd. All rights reserved.