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  • G&C Plumbing and Heating

What Is the Purpose of An Expansion Tank on A Water Heater?

Wondering what a water heater expansion tank is, and why it’s an important element of any tank-based water heater? In this guide from G&C Plumbing, we’ll discuss the basics of this water heater component, and help you understand how it works – and why it’s important. Let’s get started.



Water Expands When It’s Heated in Your Water Heater


Like the vast majority of other substances, water expands when it’s heated.


This is because when heat is applied to water, this causes the molecules to become less dense, which means that the volume of the water itself becomes higher.


If you’ve ever heard of a water heater exploding, this is why – uncontrolled increases in pressure have caused the tank to rupture.


As water heats up, it can expand dramatically, and if it’s hot enough to turn into steam, this can add even more pressure to the water heater.


If the relief valve is malfunctioning, this can lead to an explosion.


In the past, expanding water in the hot water heaters would simply be released back into the main water supply where it came from – relieving excess pressure.


Today, though, this is prevented by a “check valve.”


This valve prevents water backflow, which is necessary because wastewater sent back to the water supply by a home could contaminate the fresh water supply.