This brand is the # 1 choice of Physicians. It’s true HEPA Filtration Efficiency is 99.97% effective at removing particles as small as 0.3. The size of a common microscopic particle in the air is of 1.0 micron (1/25,000 of an inch), which includes pollen, dander, smoke, and mold spores. Running your HEPA filter 24/7 in a sterile or semi-sterile environment will help insure that contamination is either none existent or very low. Comes with a 5-year Manufacturer's Warranty. AHAM Certified for rooms up to 9' X 12'. Also serves well if used as a flow hood.