We have a partially finished basement with family room, bedroom and full bath.  The other half is unfinished and is where we have our litter boxes for the 2 fur babies.  We could tell a difference in air quality within several hours of setting up the two units we purchased.  We have one in family room and the other within 10 feet of the litter boxes in unfinished part of basement.  So far, we are very happy with our purchases.