I, too, love the air purifier and actually can tell when the filters need to be changed because my breathing changes and I wake every morning with a headache. As I use this only during the night, I would think the filter would last longer despite the claim that circumstances can affect how often both the carbon prefilters and the HEPA filters need to be replaced. I actually have to replace my HEPA filter about every three to four months, but that is in large part because my large Chesapeake Bay