The answer to 'air duct grimy' is that air ducts can become grimy and dirty over time due to a buildup of dust, debris, and even mold. This can happen for a few common reasons, such as poor home ventilation, pet dander, or simply the natural accumulation of airborne particles circulating through the ductwork.
Some of the key symptoms of grimy air ducts include reduced airflow, musty odors, and visible dirt or debris coming out of the vents. If left uncleaned, this can lead to reduced indoor air quality and potentially exacerbate allergies or respiratory issues for household members.