The Eurovent Association has released the fourth edition of the widely-applied Eurovent Recommendation 4/21 – ‘Energy Efficiency Evaluation of air filters for general ventilation purposes’. The updated guidelines set out a new method for the determination of the annual energy consumption for filters operating at an airflow rate other than nominal. 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.