The answer to 'when to service ductwork' is that you should have your ductwork inspected and serviced regularly, typically once a year. Proper ductwork maintenance helps ensure your HVAC system is operating efficiently, improves indoor air quality, and can extend the lifespan of your system.
During a ductwork service, an HVAC technician will inspect the ducts for any damage, leaks, or blockages. They may also clean the ducts to remove built-up dust, debris, and contaminants. Regular ductwork service is an important part of your home's HVAC maintenance routine.