I purchased two 45i's for my living/dining area, which is around 400 sq ft, and my bedroom, which is around 250 sq ft. While the 45i's are rated to cover a higher area, having them for the smaller area allows us to run them on low and still maintain the desired "blue" status. These purifiers run very quietly and do an excellent job cleaning the air. Customer service from Alen is excellent. I looked at other air purifiers at the same price point, and determined the functionality, coupled with the coverage made this an obvious choice. These purifiers are very very quiet, and look good. Would highly recommend these to anyone.