How often you have the ductwork cleaned will depend on a few factors, including:
The number of people and pets in the house.
Whether anyone in the house suffers from allergies.
Whether there has been a recent severe weather event such as a dust storm.
How often you leave the windows and doors open.
In general we recommend having your ducts cleaned every 2-3 years. But if you regularly open the windows to get fresh air that should probably be every 1-2 years. Also, if you’ve never had them cleaned the time to do so is now.