First thing, check your furnace filter. Whatever dirt that is collected on your furnace filter is only a small portion of what’s in your air ducts. If your furnace filter is extremely dirty, chances are it is time to clean your air ducts. You can always check your return air grills for any amount of dust buildup, or take a look inside your hot air registers for debris, dust, and other air contaminates.
Also, if you notice any of the following when your furnace is on, then you should consider having your air ducts cleaned: unpleasant odors, poor airflow, or cold spots.
The quality of air in your home is very important. A dirty duct system can make it very uncomfortable for someone who has allergies, asthma, or other respiratory problems. It can cause headaches, nasal congestion, or other sinus problems at night or early in the morning.
The biggest improvement after cleaning your air ducts is the amount of dust that settles on your furniture. You will hardly notice any!