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Categories: Water Heaters

What Is a Thermal Expansion Tank?

thermal expansion tank attached to a water heater Did you ever think there were so many things related to water heaters? In our continuing theme of water heaters, today’s discussion will focus on thermal expansion tanks.

You may have seen them before and not even realized what they were or what function they provide. They look like a small propane tank installed above a water heater. And, while they look simple enough, they offer a critical safety function.

As the water in your water heater heats up, it expands. As it expands, pressure builds up within the tank. In the past, when the hot water expanded, water would be pushed back into the city or municipality’s “main” to relieve the pressure.

However, with this method, there was a risk of water contamination as it moved back into the city/municipality water system. In 1992, the EPA started requiring city/municipality water providers to protect the integrity of their water, and this was the start of what is broadly known as “backflow” technology.

As discussed previously, high water pressure can be invisible yet very dangerous. Without a thermal expansion tank, valves can leak at 150 PSI and 210F. This pressure can damage or even destroy your plumbing system, appliances, and fixtures, eventually rupturing your water heater tank.

A thermal expansion tank works pretty much behind the scenes and is installed above your water heater. The tanks contain an air bladder, which must be pressurized with air to your personal incoming water pressure, and it expands and contracts to absorb the expanded water from the water heater.

As the pressure in your water heater rises, this tank provides a place for the excessive water to move to until the pressure is normalized. This reduces the pressure building up in your water heater because the water now has somewhere to go. Without it, the pressure continues to build, and, in time, this can cause the high water pressure problems we discussed.

You may not have a thermal expansion tank and may feel that your water heater works just fine. But remember, high water pressure, like high blood pressure, can often go undetected and cause tremendous damage behind the scenes.

You may be grandfathered in, and the new requirements only apply to you once you replace your existing water heater. Just because it may not be required doesn’t mean you shouldn’t consider installing one.

A thermal expansion tank will extend the service life of your water heater by keeping the pressure normalized and consistent. It will eliminate the constant pressure fluctuations that can be damaging if left undetected. While there are many reasons to install a thermal expansion tank, your “peace of mind” should also be a benefit.

A thermal expansion tank is relatively maintenance-free, but that doesn’t mean you can “set it and forget it.” It should be periodically checked for proper pressure and to determine if it has become waterlogged and hit the end of its life span, needing replacement before it corrodes and leaks.

Thermal expansion tanks do not last as long as your water heater and stop working long before the water heater does, leaving your water heater unprotected. A great time to have it replaced is when you have your yearly water heater flush done.

The pressure can be checked by attaching a tire gauge to the valve, usually located at the bottom of the tank. It should match the average water pressure in the home.

A thermal expansion tank only has a one-year guarantee because if they do their job, they’ll become waterlogged. If not checked and replaced, they can split and leak. They can be dangerous, like throwing a can into a bonfire. If maintained and working properly, they help keep the water pressure even throughout the house while the water is heating.

At Three Way Plumbing, we’re happy to discuss thermal expansion tanks and answer any questions you might have.

Remember, we’re only a phone call away at (704)-795-9349. Contact us today.

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