What should be checked regularly to maintain an HVAC system’s efficiency?

Regularly checking the refrigerant levels is vital for maintaining an HVAC system’s efficiency because the refrigerant is essential for heat exchange processes within the system. Proper refrigerant levels ensure that the system operates at optimal cooling or heating capacity. Low refrigerant levels can lead to reduced efficiency, increased energy consumption, and potential damage to the compressor. This can result in costly repairs and decreased comfort levels in the conditioned space. Regular monitoring and maintaining the correct refrigerant charge not only enhance efficiency but also prolong the lifespan of the HVAC system.

The other options may have some relevance to HVAC maintenance, but they do not directly contribute to regular efficiency monitoring in the same way that refrigerant checks do. The size of the ductwork is typically determined during the initial design and installation of the system and doesn’t change over time, while the age of the system is more related to end-of-life considerations rather than ongoing efficiency. The color of the filters can indicate when they need changing, but it's not a direct measure of operational efficiency.