What is the recommended "A" dimension for a one pipe parallel system with a dry return?

In a one pipe parallel system with a dry return, the "A" dimension typically refers to the minimum distance between piping and other structures or existing systems to ensure proper function, installation, and maintenance. The recommended "A" dimension for such systems is often set at 28 inches. This measurement helps provide sufficient space for thermal expansion, contraction, and allows for proper installability and access for repairs or replacements. Ensuring this clearance also helps prevent issues related to vibration, noise, and maintenance difficulties that could arise if the piping were positioned too closely to other structures.

While different system designs may vary based on specific application requirements or regulations, 28 inches stands as a common standard in the industry that balances functionality and safety in the context of a dry return system.