The Blueair 503 air purifier is for rooms up to 580 square feet. Blueair’s HEPASilent technology captures 99.97% of harmful particles such as dust, pollen, and bacteria, down to 0.1 microns in size. Blueair air purification systems use both types of filtering, electrostatic and mechanical filtration to deliver clean air efficiently. The Blueair 503 is equipped with SurroundAir™, which takes in air from the bottom and sides, releases it from the top and sides, and has greater inlet and outlet areas, to diffuse airflow and reduce draft while maintaining an extremely high air flow. How do you know when to change a filter? There is a magnetic filter timer included that you can place anywhere you like, on the side of the filter or even in your kitchen to remind you to replace the filter. You can easily replace filters by removing the top of the unit and sliding out the old filters. The Blue air 503 was independently tested alongside 22 other air purifiers by The Consumer Rights Protection Commission of Shanghai and rated the best in performance for removal of fine particles (PM2.5) and formaldehyde. There are no drafts no matter what fan speed you choose. It takes in air from three sides, releasing clean air from the top and sides, reducing draft and maximizing clean air delivery. The 503 also has wheels to make it easy to move around.