I found the Alen BreatheSmart purifier on line after returning home from vacation and getting a severe headache from 3 dogs in the home. After getting the purifier, very quick shipping, I hooked it up and the headache was gone witin 12-18 hours. Neighbors remarked how the house doesn't have doggie odor(severe, before) and asked what I had gotten. I would recommend this to anyone..even on high the sound is no more than the heat or air coming on.