What is an expansion tank used for in plumbing?

An expansion tank in plumbing serves the important purpose of absorbing excess pressure that arises when water is heated. When water is heated, it expands, increasing the pressure within the plumbing system. If this pressure isn't managed, it can lead to issues such as leaks, damaged pipes, or malfunctioning fixtures. The expansion tank is designed to accommodate this increased volume of water by providing a space where the expanded water can go, thus maintaining a balanced pressure in the system. This prevents potential damage and ensures the safe and efficient operation of hot water distribution in plumbing systems.

The other choices are not accurate representations of the function of an expansion tank. It does not provide hot water to fixtures, as that function belongs to the water heater. While it is crucial for maintaining pressure, it does not filter impurities from the water or cool down hot water before it enters the piping. Instead, its primary role is solely focused on managing pressure fluctuations caused by thermal expansion.