The Dual Filter is a combination of a HEPA H12 filter and an activated carbon filter. The HEPA filterremoves pollutants such as fine dust, pollen, viruses and bacteria from the air while the activatedcarbon filter adsorbs gases - unpleasant odours, tobacco smoke, VOCs, etc.. The H12 HEPA filter isnot as dense as the H14 HEPA filter which means that it can filter more air over the same period oftime. The Dual Filter will need to be replaced every 8-12 months. Roger big requires two H12 DualFilters.