Replacement Bionaire 911D Humidifier Filter - Compatible Bionaire 911D Air Filter Replacement Bionaire 911D Humidifier Filter Replaces Bionaire 911D Air 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!