3 - STAGE FILTRATION system includes a pre-filter, a 1" thick activated carbon filter, and a High Efficiency Filter which captures 99. 7% of microscopic particles on silent mode including dust, pollen, smoke, and pet dander. Great for homes with pets, babies, or young children. Most ideal for those who suffer from seasonal or non-seasonal allergies or those who just want fresh, clean air in their home. SMART CIRQULATE SYSTEM uses a particle sensor to continuously monitor your indoor air, adjusts the air400's speed of air flow accordingly, and provides real-time feedback on the front digital display. No more wondering if your air purifier is working! POWERFUL PERFORMANCE & THOUGHTFUL DESIGN air400 is powerfully equipped with a large fan and long-lasting, quiet, digital DC motor. Built to blend right you're your home with a neutral tone, clean edges, and sleek design. LIBRARY QUIET air purification. The air400 has an automated dimming night mode and provides the air purification at noise levels as low as 30 db(A) on silent mode. Recommend for medium to large rooms between 300 and 400 sq. ft. The air400 is best suited for large bedrooms, kitchens, living rooms, and basements. This air purifier can exchange the air in a 400 sq. ft. room 3 times every hour Every air400 comes with 1 Activated Carbon filter and 1 High Efficiency + Pre combo filter. The air400 also has a filter replacement indicator. We recommend that the filters be changed once every 6 months depending on use