Air filters trap dust, pollen, pet dander, and other particulate and stop them from circulating throughout your HVAC system and living space. Once they become dirty or clogged airflow is hampered, efficiency is reduced, and indoor air quality is lowered. While you may be able to manage three months or longer without having to change your air filters, factors such as owning pets and other indoor air quality issues may increase the frequency of needing to replace your filters.