The Aerus Guardian Angel Air Purifier is a sealed, true HEPA air purifier with the ability to filter an average size room (10X10) with 9 air changes per hour. This means that the entire room can get a breath of fresh air approximately every 7 minutes. Aerus Guardian Angel air purifier has been highly recommended by doctors and is commonly used in hospitals, laboratories, and computer rooms. Additionally, the HEPA (high-efficiency particulate absorbing) filtration used inside the Guardian Angel air purifier features Photocatalytic Oxidation which will eliminate harmful contaminants in the air.