Summary: This HEPA purifier does a great job of purifying the air for a good-sized room. I've been using it in my master bedroom for several weeks now and have noticed an improvement in terms of a significant decrease in dust, contaminants, and odor. For maximum applicablity, Honeywell suggests leaving the unit on all the time. One downside of the air purifier is the fact that it can be quite noisy at medium and high settings. However, a permanent HEPA filter that just needs occassional vacuuming is a big plus in terms of saving money.