What is the main purpose of an expansion tank in a hot water heating system?

The main purpose of an expansion tank in a hot water heating system is to absorb excess pressure resulting from the thermal expansion of water as it heats up. When water is heated, it expands, and without a means to accommodate this increased volume, pressure can build up in the system, potentially leading to damage or failure of pipes, fittings, and appliances. The expansion tank provides a designated space for this expanded water to flow, thus maintaining the integrity and safety of the heating system.

This crucial function not only protects the system but also ensures efficient operation and longevity of the hot water heating setup. Other options, such as increasing water temperature, facilitating water filtration, or enhancing aesthetic appeal, do not align with the primary operational role of an expansion tank.