Which maintenance step is vital for the longevity of a heat pump?

Cleaning or changing filters frequently is essential for the longevity of a heat pump because the filters play a crucial role in maintaining proper airflow through the system. When filters are dirty or clogged, they restrict airflow, which can lead to inefficient operation and increased energy consumption. This not only strains the heat pump's components but can also result in overheating and premature wear. Regular maintenance of filters helps to ensure that the system operates efficiently, which in turn can prolong its lifespan and optimize energy usage.

In contrast, while checking thermostat batteries can be helpful, it does not directly affect the operation or longevity of the heat pump. Insulating exposed ductwork can improve efficiency as well, but it is not as immediate a maintenance step as managing filter conditions. Limiting the use of the system to only winter months would ignore its potential for cooling and lead to unverified wear from inactivity. Hence, maintaining clean filters is the most critical step among the options provided for ensuring optimal performance and extending the life of a heat pump.