The Dual Filter is a combination of an H14 HEPA filter and an activated carbon filter. This adsorbsgases such as unpleasant odours, VOCs, tobacco smoke, etc. while the HEPA H14 filter part removespollutants such as viruses, bacteria, fine dust and pollen from the air. The H14 HEPA filter has agreater density than the HEPA H12 filter, enabling more particles to be removed from the air per airchange. The Dual Filter will need to be replaced every 8-12 months. Roger big requires 2 DualFilters.