During the Eurovent Summit in Seville, members of the Eurovent Product Group ‘Air Filters’ have approved the third edition of amended Recommendation 4/21-2018 ‘Energy Efficiency Evaluation of Air Filters for General Ventilation Purposes’. The first edition of this recommendation, published back in 2014, was a pioneering publication addressing the energy efficiency of filters. At that time it was referring the long-established but already obsolete EN 779. The second edition (2016) implemented the ISO 16890 classification and testing methods in place of EN 779. This edition, developed using test data collected throughout 2017 and 2018, introduces a modification of the total amount of dust fed for rating. The amendment aims at better matching of energy evaluation outcomes obtained from EN 779 and ISO 16890 based calculation methods. This Eurovent Industry Recommendation, available in the English language, supersedes all of its previous editions, which automatically become obsolete with the publication of this document.