"Portable True HEPA Air Purifier Replacement Filter Kit includes two replacement filters. Dual HEPA filters (filter lifetime is 1600 hours or approximately 1 year of use in a school setting). Air purification is a key component in improving air quality indoors. There are many benefits to having good air quality including increased student engagement, improved well-being for allergy and asthma sufferers and reducing the transmission of viruses, including COVID-19. The virus spreads through aerosolized particles that tend to hang in the air unless they are blown away or removed; air purifiers can do both. To prevent the spread of airborne viruses indoors, the air should be refreshed five to six times per hour, however, over half of existing school and building ventilation systems are outdated and achieve less than that. Placing portable air purifiers in these spaces helps reduce the amount of airborne contaminants, including viruses by refreshing and purifying the air as it passes through its filters. *The Portable True HEPA Air Purifier is designed for an average classroom that is 750 sq ft, with ceilings at 8 ft height. Fan speed, ceiling height, age of HVAC and other ventilation are all variables that affect total air changes per hour (ACH). To achieve optimum air purification for your room size, please contact your Copernicus representative to calculate the right number of units for your space. You will need to provide the room size and ceiling height. "