Water Heater Expansion Tanks: What They Are and Why They’re Amazing

Thumbnail Image Credit: Benjamin Franklin

Ever noticed how we only think about our water heater when something goes wrong? Well, one way to avoid trouble is by installing a water heater expansion tank. This small, often overlooked piece of equipment is essential in maintaining your plumbing system, especially in homes with modern setups. Without it, pressure buildup can damage your water heater and pipes, leading to costly repairs. But what exactly is an expansion tank, and why do you need one?

In this article, we’ll break down the basics of water heater expansion tanks, their benefits, how to size them correctly, and what maintenance they need to keep your system running smoothly.

What Is a Water Heater Expansion Tank?

A water heater expansion tank (or thermal expansion tank) is a small tank that helps manage the pressure caused by expanding water when your water heater heats up. Think of it like a safety valve for your plumbing system. As the water heats and expands, the tank absorbs that extra volume, preventing dangerous pressure buildup.

Without this safety feature, the pressure can stress your water heater and pipes, leading to leaks, ruptures, and even system failure. Before the use of backflow prevention devices, excess water pressure could escape back into the public water supply, but now, that’s no longer an option. This change makes expansion tanks more important than ever.

Why You Need a Water Heater Expansion Tank

If your home has a “closed” water system—meaning it uses backflow preventers or check valves—then installing a thermal expansion tank isn’t just a good idea; it’s often required by building codes. Closed systems trap pressure inside, and if that pressure doesn’t have somewhere to go, your plumbing can suffer.

Here’s why an expansion tank is a crucial addition to your water heater:

• Prevents Pressure Damage: As water expands when heated, the tank provides space for this extra volume, easing pressure on your pipes.
• Extends Heater Life: High pressure can cause wear and tear on your heater’s valves, leading to early failure. A thermal expansion tank reduces this stress.
• Reduces Risk of Leaks or Ruptures: Too much pressure can cause pipes to burst or leak. By keeping pressure in check, you avoid these costly problems.
• Saves You Money in the Long Run: While installing a tank costs money upfront, it can save you from expensive repairs and extend the life of your water heater and plumbing system.

How to Choose the Right Expansion Tank Size

Not all water heater expansion tanks are created equal. You need to size your tank correctly for it to function as intended. The size depends on two factors: your water heater’s capacity and your home’s water pressure.

Sizing Guidelines:

• For water heaters up to 60 gallons:
  • If water pressure is below 60 psi, a 2-gallon expansion tank will do.
  • If water pressure is 60 psi or above, opt for a 3.2-gallon tank.
• For water heaters over 60 gallons:
  • For water pressure below 50 psi, use a 2-gallon tank.
  • For water pressure between 50–60 psi, go with a 3.2-gallon tank.
  • For water pressure over 60 psi, you’ll need a 4.4-gallon tank.

If you’re unsure of your home’s water pressure, a pressure gauge is an inexpensive tool that will give you the answer. It’s also fine to size up if needed—an oversized tank won’t harm your system.

Installation and Cost

Installing a water heater expansion tank typically costs around $200, depending on your location and the ease of access to your system. While it’s possible to install one yourself, it’s always wise to hire a professional plumber to avoid costly mistakes. If installed incorrectly, an expansion tank could cause more problems than it solves.

Testing and Maintaining Your Expansion Tank

Although an expansion tank is a reliable addition to your plumbing system, like all equipment, it needs occasional maintenance. Here’s how to keep your expansion tank in good shape:

• Check the Pressure: Expansion tanks are pre-charged to about 40 psi, but the pressure should match your home’s water pressure. Use a tire pressure gauge to check the tank annually. If the pressure is off, it can easily be adjusted using a hand pump.
• Test the Schrader Valve: This valve releases air from the expansion tank. If water comes out when you press it, the tank’s bladder has ruptured and the entire unit will need to be replaced. If only air escapes, you’re good to go!
• Listen for Pressure Issues: You can tap the top and bottom of the tank with a metal object. If the sounds are the same, the tank might not be functioning properly. In a healthy tank, the top (filled with air) should sound different from the bottom (filled with water).

Most expansion tanks last between 5 and 10 years, but regular maintenance will help extend their lifespan. If the tank does fail, replacing it is usually straightforward and inexpensive compared to dealing with a damaged water heater or plumbing system.

Common Signs of a Faulty Expansion Tank

How can you tell if something’s wrong with your expansion tank? Here are some red flags to look out for:

• Unusually High Water Pressure: If water gushes out of your faucets with more force than usual, the expansion tank may not be absorbing excess pressure.
• Water Heater Problems: If your water heater is making odd noises or showing signs of leaks, the expansion tank may not be doing its job.
• Frequent Relief Valve Leaks: The temperature and pressure (T&P) relief valve is a backup for when pressure gets too high. If it’s frequently releasing water, the expansion tank may not be absorbing the extra pressure properly.

Are There Any Drawbacks?

While water heater expansion tanks offer big benefits, there are a couple of minor drawbacks:

• Susceptible to Failure: Like any equipment, expansion tanks can wear out, especially if they’re not maintained. But compared to water heater or plumbing failure, this is a minor issue.
• Installation Challenges: Installing the tank incorrectly can lead to issues, so if you’re unsure about doing it yourself, it’s always best to call a plumber.

Final Thoughts: Is a Water Heater Expansion Tank Worth It?

In the world of plumbing, small upgrades can make a big difference. A water heater expansion tank may not seem like a flashy addition, but it’s one of the most important for keeping your system safe and functioning smoothly. It prevents costly pressure damage, extends the life of your water heater, and offers peace of mind, knowing your home’s plumbing is protected.

If your water heater doesn’t have an expansion tank, it’s worth considering one. They’re affordable, take up little space, and can save you from big problems down the road.

Call 1-Tom-Plumber 

Don’t hesitate to contact us here or call us at 1-Tom-Plumber (1-866-758-6237) if you need any plumbing, drain cleaning, water damage, or excavation service. 1-Tom-Plumber’s certified team of plumbers and drain technicians respond immediately to any emergency plumbing, drain cleaning, or water damage problem. We also handle the excavation of underground water lines and sewer main lines. Our immediate-response team is available every day and night of the year, even on holidays.