
We started with 2 and have just ordered 3 more. We have a serious family problem with mold and fungus and this was part of the plan to overcome it. The obvious difference in the air quality prompted us to order more (one for each of the kids to take back the dorm and apt.) and cover even the rooms that didn't seem to have mold problems. Our house is very old and big. The low cost has made it possible for us to get more coverage for much less than we expected.