What type of system primarily relies on refrigerant lines?

The primary function of refrigerant lines is to transport refrigerant between different components of a system, allowing for the exchange of heat. In the context of HVAC systems, both heating and cooling systems utilize refrigerant lines to facilitate this heat transfer process.

In cooling systems, refrigerant absorbs heat from inside a building and releases it outside, effectively lowering the indoor temperature. Conversely, in heating systems that use heat pumps, the refrigerant absorbs heat from the external environment and transfers it indoors to provide warmth. This dual functionality is integral to heat pumps, which can operate in both heating and cooling modes based on the direction of refrigerant flow.

Therefore, since refrigerant lines are essential for both heating and cooling processes, it confirms that the correct answer encompasses both types of systems. This is why the option indicating that both heating and cooling systems rely on refrigerant lines is accurate.