What is the purpose of an expansion tank in a closed heating system?

The purpose of an expansion tank in a closed heating system is to accommodate the thermal expansion of water and maintain system pressure. As water heats up, it expands, leading to an increase in volume. If this expansion is not properly managed, it can result in excessive pressure buildup within the system, which can potentially cause damage to the pipes, fittings, or even appliances.

The expansion tank provides a space for this expanded water to go, effectively absorbing the increase in volume. Typically, it consists of a chamber that separates water from air using a diaphragm. As the water expands, it fills the expansion tank, and the diaphragm compresses the air on the other side, which helps to balance the pressure in the entire system. This mechanism ensures that the system pressure remains within safe operating limits, preventing leaks or failure.

While reducing water pressure can be a benefit in some cases, it is not the primary purpose of the expansion tank. Enhancing heating efficiency and storing excess water are also not key functions of the expansion tank. The primary role is to manage pressure fluctuations resulting from thermal expansion.