We have lived in our current home for 15 years and have battled dust since the beginning. We like to have our windows open when the weather is agreeable, so we accept it. We decided to try the large SANS air purifier to see how it works, but we weren't really expecting much. After just a couple days, we couldn't believe how much better the air was. Virtually no dust. We are not dust moping our floors every other day anymore. After two or three weeks, we decided to buy the smaller one for our master bedroom. We can't believe how much cleaner the house is now. We're due for filter change for the big purifier beginning of September and I'm very curious to see how dirty the filter is considering how much cleaner our house is since deploying SANS in our home. We are believers and converts now!