The Shark HP202 Air Purifier Max senses air quality and automatically adjusts. This is a very quiet air purifier and was very easy to set up and use. As a caution make sure that you remove the plastic wrap from the filter before using. I love that this captures much more of the harmful micro-pollutants than some of the other air purifiers, because that makes me confidant that I am living in the cleanest possible air within my home. This filtrates up to 1200 square feet and is based on one air change per hour. Having seasonal allergies and a husband with asthma it is super important to me to have the best air purifier around and this goes above and beyond my wildest expectations. One important feature to me is that this is able to mechanically capture airborne droplets in the air that can possibly carry bacteria and viruses!  This is a very reliable high quality air filter and I highly recommend it !!!