You should have your ducts cleaned every 3-5 years, depending on if you have pets or have had renovations done.
(With renovations, it is suggested to clean them immediately afterwards).
This will provide:
1 – Healthier air quality in your home/business
2 – Less dusting and vacuuming
3 – Preventative maintenance for your HVAC (Furnace, AC etc.) equipment with
less filter changes.