Air ventilation systems often account for the lion’s share of a building’s energy consumption and the pressure drop in air filters accounts for a larger portion of the total pressure drop in a ventilation system. Thus from the viewpoint of increasing energy efficiency, there are strong reasons for optimising the choice of air filters without compromising filtration requirements. A life cycle cost can be made in different ways depending on application and purpose of the air filters. This Recommendation prepared by the Eurovent WG 4B ‘Air Filters’ gives a guideline, for calculating life cycle cost of air filters and a tool to minimise the running costs of an air handling installation.