The Filtrete 16x20x1 Flat Air Filter, made by 3M, helps capture unwanted particles from your household air to contribute to a cleaner, fresher home environment. Use these two 3-month 1-inch home air filters in your furnace, air conditioner or HVAC system. For optimal performance of your heating and cooling system or HVAC system, change your furnace filter at least every 90 days.