The cost of operating an air filter depends on the energy efficiency of the device, though power consumption is usually a secondary factor. Keep in mind that air purifiers require replacement filters from time to time. A high-quality HEPA filter, for example, may need to be replaced every 3 to 5 years. On average, using a purifier daily could cost between $0.02 and $0.32. In standby mode, the annual operating cost ranges from 0 cents to 0.86 cents—quite a reasonable expense considering the potential health benefits!