Addressing the airtightness of the building envelope is key to achieve thermal comfort, good performance of ventilation systems and to avoid excessive energy consumption. Previous studies have estimated an energy impact on infiltration on the heating demand between 2 and 20 kWh/(m2·y) in regions with temperate climates. In Spain, this issue has not yet been addressed in depth. This study aims to assess the energy impact of uncontrolled air flows through the building envelope in residential buildings in Spain. For this purpose, airtightness results of more than 400 blower door tests have been analyzed. Multi-family and single-family dwellings built in several periods and located in 9 regions with different climate characteristics have been studied. Infiltration was found to have an energy impact in the range 2.43 – 19.07 kWh/(m2·y) for the heating demand, whereas it is not so significant regarding the cooling demand. The obtained results show great potential for energy saving in the country.