It is recommended to replace your air filter once a month to make sure your heating and cooling system is running efficiently. Air filters help remove dust mites, pet dander, hair, and other pollutants in the air. If you do not change your air filter it can cause issues with your furnace or air conditioning unit. In order for your home to be heated or cooled correctly you need to make sure the air is flowing freely. It is also especially important for those with allergies as it can help remove a lot of dust from the air. Here is a video on how to replace your air filter yourself provided by HowToWith GEO.