Which piping code section is mainly used for the design and installation of HVAC piping systems?

The correct choice for the design and installation of HVAC piping systems is primarily found in B31.9. This section of the piping code specifically addresses the requirements for low-pressure and high-pressure piping systems in buildings, including those used for heating, cooling, and plumbing. B31.9 covers aspects such as materials, design considerations, installation practices, and testing procedures that ensure HVAC systems operate safely and efficiently.

While other sections like B31.1 (Power Piping), B31.3 (Process Piping), and B31.5 (Refrigeration Piping) also provide guidelines for various types of piping, they do not focus specifically on HVAC systems. B31.1 is primarily aimed at power plants and industrial facilities, B31.3 deals with process piping, typically found in chemical plants, and B31.5 is centered around refrigeration applications. Thus, B31.9 is tailored to meet the specific needs of HVAC systems, making it the correct reference for this particular context.