I have 4 honeywells here. I couldn't live in the same house with cats without them. They help immensely. I notice a difference whenever I sleep outside my home, how less clean the air is. I also moved to a new apartment so I think that helps a lot too. Before I moved in with my GF and her 2 cats, I used the honeywell in my bedroom, and I always felt the immediate difference if I went a night without it on, I would wake up being a bit more congested in the nose and coughing a bit more. I'm not sure if it's CF related or just allergies though, hard to tell, hope this helps. I'd like to invest in the kind that auto-detect the air quality and save energy by changing the fan speeds, but not sure if it would make a difference because of the cats.