The answer to 'air duct filthy' is that filthy air ducts are a common problem that can lead to poor indoor air quality, increased allergens, and reduced HVAC efficiency. Common causes include dust buildup, pet dander, mold growth, and pest infestations. Symptoms may include visible dirt or debris in the ducts, musty odors, and respiratory issues for occupants.
The best solution is to have your air ducts professionally cleaned every 3-5 years, or more frequently if you have pets, smoke indoors, or notice visible buildup. DIY duct cleaning is possible but requires specialized equipment and carries risks if not done properly. It's generally recommended to hire a certified HVAC technician for a thorough, safe cleaning to ensure your ducts are properly maintained.