Make sure you change your air filter every 3 months or 90 days if you live in the suburbs. If you seldom visit your house or if you live alone and oftentimes spend more hours at work, then you can change your air filter every 6 – 12 months. However, if you have a pet, you ought to change it every 2 months. If you have more than one pet or if anyone at home has allergies, make sure to clean it every 20-45 days.