Windows have been under study for the last decade due to their improvements and for being the lowest thermal resistance component of the facades. Amongst this component, the building also loses heat as a result of airing needs. Thermal losses through windows and ventilation may represent a large percentage of the whole thermal losses of the building. The double ventilated window is one of several construction systems that preheat the incoming air. It also reduces thermal losses through windows, reducing the heating load of the building. Several studies have shown the performance of the ventilated double window under different climatic conditions as well as the influence of different inputs. This paper shows how this passive air heating system can be improved in order to collect more solar heat. Thermal balance was improved by 8.4% and 12.5% in Braganca and Evora, respectively, while the delivered air temperature increased from 9.8 degrees C to 11.9 degrees C and from 13.5 degrees C to 17.4 degrees C in Braganca end Evora, respectively. (C) 2017 Elsevier Ltd. All rights reserved.