A dirty filter in your HVAC system will raise your energy bills. A dirty filter restricts the air flow into your HVAC systems air handler, causing it to work harder to cool or heat your home.
A dirty clogged filter can restrict HVAC airflow and potentially cause problems with the system. They also cease to filter allergens and other particulates out of your air.
Cost of repair
Dirty, unchanged filters can make your HVAC system fail completely. Repairing a broken HVAC system can end up costing you a pretty penny.