The main difference between an air purifier and an air filtration system is the way they clean the air. An air purifier uses internal fans and filters to capture and remove pollutants from the air, such as dust, pollen, and pet dander. An air filtration system, on the other hand, works with the home's existing HVAC system to filter the air as it passes through the ductwork. Air filtration systems can capture smaller particles than air purifiers, but they are typically more expensive and require professional installation.