When should the HEPA filters be replaced ?

The average HEPA filter, properly installed, and with frequent changes of the prefilter, should last from five to eight years. There are always unusual cases: filter used to capture radioactive particles or pathogenic organisms should, of course, be changed when they become unsafe for use. Otherwise, the resistance of the filter as indicated on a monometer or the air flow measured with a velometer are indications of need for a change.