UpStart Battery 4-Pack Replacement Bionaire BCM5520RC Humidifier Filter - Compatible Bionaire BWF100, HWF100 Humidifier Filter Replacement Bionaire BCM5520RC Humidifier Filter; Quantity, 4 Replaces Bionaire BWF100, HWF100 Humidifier Filter Traps Water Impurities & Dissolved Solids Before They Become Airborne For best results, change air filter at least once per season or more often depending on air quality and use. Essential for Allergy Sufferers. On Sale for a Limited Time!