HVAC connection details are essential in system design as they provide a comprehensive overview of the required ductwork and piping connections, support requirements, and miscellaneous appurtenances for a proper installation of HVAC equipment. These details cannot be adequately shown on floor plans or large-scale plans, making them a critical component of the design process. By including connection details, HVAC system designers can ensure that all necessary components are accounted for, and the system is installed correctly and efficiently.