Central air-conditioning units can be integrated with central ____________.

Central air-conditioning units can indeed be integrated with central heating systems. This configuration is commonly known as a "forced air" system. In such setups, both the heating and cooling functions utilize the same ductwork, allowing for an efficient distribution of conditioned air throughout the home.

When integrated with a central heating system, the air conditioning unit can share the blower or fan that circulates air, making the system more efficient and reducing the need for additional installations. This integration also allows for better control over indoor climate, as both heating and cooling can be managed through a single thermostat, providing convenience and enhancing energy efficiency.

While ductless systems are a popular alternative for air conditioning, they operate independently without requiring ductwork, making them a different approach. Air filters and thermostats typically work alongside heating and cooling systems but do not represent a fundamental integration of the heating and cooling systems themselves. Thus, the correct association is clearly with central heating systems.