Given the high impact that air leaks have on buildings’ energy expenses, most developed countries have set out norms which regulate their presence in homes. Chile will soon begin this process; however, the airtightness revision strategy in envelopes has not been resolved as of yet. This article presents a tool to Assess Airtightness in Design, EHeD. The software will allow predicting the performance of homes under the regulations which will be set out, aiding designers, builders or owners to make decisions when making changes to improve airtightness. EHeD has been validated through pressurization tests in diverse homes across the country, with results that are in line with expectations, thus validating its calculation model. The methodology considers three stages: determining the main factors that have an impact on the airtightness in Chilean homes, preparing an airtightness database for each component (wall, windows and doors) and preparing a calculation model that is integrated in an IT interface.