Well, our IQAir HealthPro Plus told us that it wanted a pre-max filter change. We didn't realize how important that filter was until we actually changed it out. The old one was filthy black. After using the air cleaner with the new pre-max filter in it, we realized that this air cleaner is a jewel. The air is so much fresher, cleaner, and healthier. We have three of them, on of which is in the basement taking out the musty odor. We highly recommend the HealthPro Plus air cleaner, but you must keep up with the filter changes.