Air filters are an essential part of any ventilation system and make a significant contribution to indoor air quality It is important that they are selected not only on the basis of their efficiency, but also on their life cycle cost (LCC), i.e. the total cost over its lifetime. Jan Gustavsson, Camfil Farr, Sweden, explains the theory behind LCC analysis and shows how a computer, software programme can help users and designers of air handling systems select filters with optimum LCC.