Find air control accessories and filters at Target.com! The protec extended life humidifier filter removes minerals and pollutants from the unit s water. it has an antimicrobial treatment on the filter to help prevent the growth and migration of mold, algae and bacteria on the filter. it s reinforced for longer life and maximum efficiency. for best results it should be replaced about every 2 months, depending on use and the hardness of your water. This filter is for use with cool moisture humidifiers and fits the following models: vicks models; v3100, v3500 series, v3600, v3700, v3800, v3850 series, v3900 series. honeywell models; hcm-350 series, hcm-300t, hcm-315t.