We bought two of these to run at my in-laws house, as they have a cat that my husband and daughter are highly allergic to. Even though they clean before our visit and keep the cat in their room the entire time, usually after 4-5 days of staying there they are wheezing, using inhalers a lot, and having trouble sleeping.  This time...we were there for 2 weeks and the inhalers didn't even come out until day 10 or so, and then only at night really. So we feel the filters made a huge difference. And we only ran them in the rooms we were sleeping in. If we'd ran them in the main living space I'm sure that would have helped even more.  Now, buying one for home too!