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

The purpose of an expansion tank in a hot water system is primarily to accommodate the thermal expansion of water and maintain system pressure. When water is heated, it expands, leading to an increase in pressure within the closed-loop system. If this expansion were not managed, it could result in excessive pressure that might damage pipes, fittings, or even the boiler itself.

The expansion tank provides a space where the excess water can expand into, preventing potentially damaging pressure build-up. It typically contains a diaphragm or bladder that separates the air in the upper portion of the tank from the water in the lower portion, allowing for the absorption of the additional volume of hot water without affecting the overall system pressure. This ensures the system remains safe and operates smoothly during heating cycles.

In contrast, storage of excess hot water for later use pertains to a different function usually fulfilled by a hot water tank, not an expansion tank. Filtering impurities involves a separate filtration system rather than an expansion tank's function. The heating of water prior to entering the main system typically refers to pre-heating mechanisms, which also do not apply to the role of an expansion tank. Thus, acknowledging these distinctions clarifies the specific and essential role of expansion tanks in maintaining the integrity and efficiency of hot water systems