I have not been able to use one of the rooms in our house because it is next to where we keep our cats' litter boxes. There is also a tree outside the window that I am allergic to almost all year round. I was skeptical that the Alen unit would work, because it seemed improbable. BUT not only can I now sit in that room all day long, I think it has helped the allergens in the rest of the house. The main heating and ac return duct is close to where the Alen is now sitting, and I have noticed that I am more comfortable in the rest of the house. I think having the Alen filter the air before it goes into the system has had a house-wide impact! I am very impressed! I am now thinking of getting another unit. These are expensive, but they actually do what they claim to do!