What is the primary function of an expansion tank in a hydronic heating system?

The primary function of an expansion tank in a hydronic heating system is to provide thermal expansion allowance. As the water in the system heats up, it expands. If there were no way to accommodate this expansion, the increased pressure could cause damage to pipes and other components of the system. The expansion tank serves as a buffer by taking in the excess water created by this thermal expansion, preventing pressure build-up and allowing the system to function safely and efficiently.

While increasing pressure, storing excess water, and improving efficiency are important aspects of a hydronic system's functioning, they are not the main role of the expansion tank itself. Maintaining a safe pressure level and accommodating changes in water volume due to temperature variations are crucial for the system's longevity and reliability, which highlights the importance of the expansion tank’s function.