The WRF – 45 CHC package is for the U-450 device. It contains the pre-filter, 1 Activated Carbon filter, and 1 true HEPA filter. The filters need to be replaced depending on the operating hours of the device and the indoor air pollution levels from gaseous pollutants and particles. An average lifespan is one year for all three filters. The above calculations are made assuming the device operates for 12 hours each day and the indoor space is moderately polluted.