The answer to 'air duct stained' is that air duct stains are a common problem caused by a buildup of dust, dirt, and other debris inside the ductwork. This can lead to discoloration and visible stains on the visible sections of the ducts. Symptoms may include poor air flow, increased dust and allergens in the home, and musty odors.
The best solution depends on the severity of the stains. For minor stains, you may be able to clean the ducts yourself using a duct cleaning brush, vacuum, and mild cleaning solution. However, for more extensive staining or if the ducts are difficult to access, it's best to hire a professional HVAC cleaning service. They have the right tools and equipment to thoroughly clean the entire duct system and remove stubborn stains.