What Is a Water Heater Expanion Tank?

A water heater expansion tank resolves the issue of thermal expansion stressing pipes and fixtures in your plumbing system. When water is heated in a closed plumbing system, its volume increases, putting pressure on pipes and even your water heater. Most homes have a closed water supply system with backflow, check, and pressure-reducing valves that prevent water from pushing back into the municipal water supply. Thermal expansion will therefore cause water pressure to continue to increase as temperature rises.

How an Expansion Tank Works

Connected to the cold-water line upstream of the water heater tank, a water heater expansion tank, or thermal expansion tank, accepts overflow by taking on excess water volume. As water is heated, its volume may exceed the capacity of your plumbing, but the tank can hold extra volume so water pressure remains at safe levels. It’s also useful when the incoming water supply pressure fluctuates. But in a typical 50-gallon water heater, those 50 gallons of water (at 120℉), can expand to 52 gallons, which can cause serious problems.

What Does a Thermal Expansion Tank Look Like?

An expansion tank used in residential applications usually looks like a small, off-white or blue propane tank. Actual tank size may vary somewhat depending on the size of the water heater. It has an air valve on top and a threaded pipe connection on the bottom.

Expansion Tank Requirements

In most cities, thermal expansion tanks are required for residential closed plumbing systems. You may also be required by law to have one installed if your main water line is fit with a backflow preventer. Local building codes differ, so it’s important to know the requirements in your area. Installing an expansion tank can still be beneficial even if it’s not required, as it can avoid a great deal of work and expenses.

Can One Tank Work with Multiple Water Heaters?

A 2-gallon expansion tank is usually sufficient for a 50-gallon water heater. Your options include installing one tank for each water heater, or a single larger tank to serve more than one water heater on a connected system. But be sure to check with manufacturers’ specifications and local plumbing codes regarding expansion tanks.

How Long Does an Expansion Tank Last?

A water heater expansion tank can last several years, but life expectancy is generally unpredictable. The quality of the tank and water quality are a couple of factors that can impact longevity. If the tank is leaking water, has condensation, or an air blockage or looks visibly rusted or damaged, it’s time to replace it.

How Do I Test the Expansion Tank?

These tanks typically fail either because the internal rubber bladder wears out or the connection between the tank and water pipe corrodes and leaks. Proper installation is the best way to ensure the system continues to work, but you can test the thermal expansion tank. First, shut off the valve, so you can safely monitor water pressure visually, tap it with a metallic object to hear the difference in water and air, or bleed air out of the top valve (if air escapes, then the bladder is intact).

For more advanced pressure evaluations, you’ll need a water pressure gauge and air pump. A licensed plumber is equipped with these tools to accurately check your water heater expansion tank for issues.

Contact Our Anaheim Plumber

If you need help with water heater expansion tank installation or water heater repair, Home X can help. Our technicians are extensively trained in the latest plumbing technology and techniques and are committed to exceptional customer service. Request a service appointment online or call 714-586-8904 today.

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