Air Ducts Cleaning ... Dirty air ducts in your air conditioning system can be a breeding ground for mold spores, bacteria, dust, pollen and other harmful deposits. Many different contaminants can accumulate over time. Your family or office staff breathes air that is continually re-circulated through this contaminated ductwork. The National Air Duct Cleaners Association (NADCA) recommends to have your air ducts inspected every two years. Depending on your location and the conditions within your home or office, air ducts need to be cleaned every four to eight years.