Which of the following is a common method of improving HVAC system efficiency?

Regular cleaning and maintenance of an HVAC system is essential for improving its overall efficiency. Over time, dust, debris, and other contaminants can accumulate in the system, leading to reduced airflow, increased energy consumption, and inconsistency in temperatures. By performing routine cleaning tasks, such as changing air filters, cleaning coils, and inspecting ducts, the system can operate more effectively. This maintenance ensures that the components are functioning properly and that the system can deliver conditioned air efficiently, ultimately reducing energy costs and prolonging the lifespan of the equipment.

In contrast, options like increasing duct size or adding more units may not necessarily improve efficiency and could lead to other complications, such as increased energy usage or higher initial costs. Reducing insulation would likely compromise the system's performance and lead to greater energy loss, counteracting any gains in efficiency. Thus, regular cleaning and maintenance stands out as the most effective method for enhancing HVAC system efficiency.