What is the key benefit of using a programmable thermostat?

The key benefit of using a programmable thermostat is the increased control of heating and cooling it provides. A programmable thermostat allows users to set specific temperature schedules for different times of the day or week. This means that the heating or cooling system can adjust itself automatically based on the user's routines, rather than running continuously or at inappropriate times. As a result, homeowners can ensure their homes are comfortable when occupied and save energy when they are not, leading to significant cost savings on energy bills over time.

While the other options may seem appealing, they do not accurately capture the primary advantage of a programmable thermostat. Equipment costs and installation prices are typically associated with the initial expenses for purchase and setup, rather than ongoing benefits. Automatic duct cleaning is not a feature of programmable thermostats; this is a separate system and not related to the thermostat's primary function.