For Merv 8, 11 and 13 filters, it is recommended that you change the filter at least every 3 months for optimal filtration and healthier air in your home. However, if you have pets or people with allergies or respiratory conditions in your home, it is best to change the filter every 2 months or even every 20 to 45 days. Vacation homes or homes that don't have much use can expect to change filters every 9-12 months. The general rule of thumb for pleated air filters (such as those manufactured by FilterBuy) is to replace the filter every 90 days.
As the filter traps more dirt, dust and allergens from the air, the efficiency of the filter decreases. MERV 17 to MERV 20 filters are commonly used in operating rooms, cleanrooms, and other settings that require absolute cleanliness. Filters with higher MERV ratings trap small particles more effectively than filters with lower MERV ratings.