What component in a heating system allows for the water to expand and contract?

An expansion tank is an essential component in a hydronic heating system that accommodates the expansion and contraction of water as it heats and cools. As water is heated, it expands, which increases pressure within the system. If this pressure is not managed, it can lead to stress on the pipes and fixtures, potentially causing damage or leaks. The expansion tank absorbs this excess pressure by allowing the expanded water to fill the tank, effectively reducing stress on other components of the heating system.

In contrast, a thermostat simply regulates the temperature of the heating system by controlling when the boiler should turn on or off, and a water meter tracks the volume of water used within the system. The boiler serves as the heat source, but it does not provide a mechanism for managing the pressure caused by thermal expansion. Therefore, the expansion tank plays a crucial role in maintaining the safety and efficiency of the heating system by managing the pressure fluctuations associated with water expansion and contraction.