While we’ve only had our 75 i for a couple of weeks I do feel when I’m sitting in my recliner on the main level the same as the purifier I able to breath a little easier with less congestion however my wife with her severe COPD hasn’t been able to tell a difference yet for whom I had bought the unit for as I would try just about anything to help her breathing. The unit is very quiet. Customer service is excellent!!Hopefully after using it a little longer I would be able to give it 5 stars and maybe trying a different type of filter when replacing could possibly make a difference only time will tell