The answer to 'air duct dirty' is that dirty air ducts are a common problem that can lead to decreased air quality, reduced HVAC efficiency, and increased energy costs. Some common causes include dust buildup, pet dander, mold growth, and debris from renovations. Symptoms may include musty odors, visible dust, and reduced airflow from vents.
For minor issues, homeowners can try DIY duct cleaning using a vacuum with a hose attachment or hiring a professional air duct cleaning service. However, for more extensive problems like mold or pest infestations, it's best to call in a professional HVAC technician to properly assess and address the issue.