I purchased two Duster 3000's for my high school auto body program three years ago. The units run all day long and have improved the air quality immensely. My former principal, who has asthma, could not spend any time in my shop before I purchased the Dusters. Once I started using the units she could spend as much time as she wanted in the shop with no breathing problems. I can't say enough good things about the Duster 3000's. I wish more shops would spend the money for Dusters to protect their most important asset, their employees.