The answer to 'why is my air duct dirty' is that air ducts can become dirty due to a buildup of dust, debris, and even mold over time. This can happen for a few common reasons, such as poor home air filtration, pets shedding, construction work, or simply the natural circulation of air through the ductwork.
Some signs your air ducts may be dirty include reduced airflow, strange odors coming from vents, and visible dust or debris around the registers. Regularly cleaning your air ducts can help improve indoor air quality, increase HVAC efficiency, and prevent potential health issues caused by poor air circulation.