Which of the following indicates that duct cleaning may be necessary?

Visible dust or mold growth within the ductwork is a clear indication that duct cleaning may be necessary. The presence of these contaminants can suggest that the air ducts are not only dirty, but they may also be harboring allergens and other particles that can affect air quality within the home. Dust accumulation can also restrict airflow, impacting the overall efficiency of the HVAC system. Therefore, if you notice signs of dust or mold, it highlights the need for a thorough cleaning to maintain a healthy indoor environment and ensure the system operates effectively.

In contrast, increased energy efficiency, recent system installation, and consistent thermostat settings do not inherently indicate a need for duct cleaning. Increased efficiency typically suggests the system is functioning well, while recent installation usually means that ducts are likely clean. Consistent thermostat settings might show stable system performance but do not address duct cleanliness or air quality issues directly.