i never needed an air purifier until i lived in a rain forest area of Oahu and there is a mold issue, as well as occassional vog (volcanic smog) i didn't want to use air conditioning (we have wonderful breezes, there's no need for it) i noticed a difference in the first 24 hours i used this. i let it run 24/7 and i'm only in the room to sleep, don't have to close up the whole house, has worked GREAT and would recommend it. it did have an odd odor for about an hour (of course it was new)