Air filters for home HVAC systems typically need to be replaced once every three months. But each home's environment is different and the exact filter lifespan may vary depending on the amount of particles in air and how often the HVAC system is used. When a filter is dirty, the air quality of the home will suffer. And filters can look clean when they are actually dirty.
With all these variables, people don’t know how often they need to change their filters. And often they forget to change their filters, resulting in poor air quality.