Addressing the airtightness of the building envelope is key to achieve thermal comfort, good performance ofventilation systems and to avoid excessive energy consumption. Previous studies have estimated an energy impact of infiltration on the heating demand between 2 and 20 kW h/(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 airflows through the envelope in residential buildings in Spain. For this purpose, airtightness results of more than 400 blower door tests have been analysed. Multi-family and single-family dwellings built in several periods and located in nine regions with different climate characteristics have been studied. Infiltration was found to have an energy impact in the range 2.43–19.07 kW h/(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.