In this study, an experimental dehumidifying system for greenhouses is tested. The system uses finned pipes fixed under the gutter of the greenhouse. The pipes are cooled below the dewpoint of the greenhouse air by cold water. The humid air passes the pipe and fins by natural convection and condensation occurs reducing the humidity in the greenhouse. The performance of the system in relation to its location and dimensions are studied by computational fluid dynamics calculations. The total heat transferred and condensate removed are monitored as a function of the greenhouse conditions. The system removes 40 g of condensate per hour per square metre of greenhouse floor from the humid air sufficient during periods when heating is applied and ventilation is minimized. The heat transferred at the cold surface by condensation is less than one-third of the total heat removed by the system at a relative humidity of 80%.