What Exactly is an Expansion Tank?

Let’s start with the basics. An expansion tank is like a safety valve for your plumbing system. When water heats up, it expands, and this expansion can create extra pressure in your pipes. This is where the expansion tank comes in. It’s a small tank with two sections—one for water and one for compressed air. When your water heater does its thing, the expansion tank absorbs the extra pressure, keeping your pipes from getting overworked.

How Does an Expansion Tank Work?

Think of it like this: When water heats up, it needs more space, but your pipes don’t magically get bigger. The expansion tank gives the water somewhere to go. Inside the tank, a diaphragm or bladder separates the water from the air. As the water expands, the air gets compressed, which takes the pressure off your pipes. It’s a simple yet genius way to keep everything running smoothly.

Why Bother with an Expansion Tank?

You might be wondering, “Do I really need this?” The short answer is yes. Here’s why:

First off, it prevents your system from getting damaged. Without an expansion tank, all that extra pressure can lead to leaky valves, busted pipes, or worse. Second, it helps your water heater last longer. Constant pressure changes can wear down your system, but an expansion tank keeps things stable. Finally, in many places, having an expansion tank isn’t just a good idea—it’s the law. Many local building codes require them, especially if you’ve got a closed-loop system.

What to Look for When Picking an Expansion Tank

Okay, so you’re convinced you need one. But how do you pick the right expansion tank? Here are the key things to think about:

Size and Capacity

The size of your expansion tank matters. If it’s too small, it won’t absorb all the pressure, and if it’s too big, it’s just taking up space for no reason. The right size depends on your water heater and your home’s water pressure. So, take a good look at those specs before buying.

Material and Durability

Expansion tanks are usually made from steel and have a diaphragm or bladder inside. The tank’s durability depends on the materials used. Look for tanks with corrosion-resistant coatings and tough diaphragms. You want something that’s built to last, so you’re not back in the market for a new one anytime soon.

Compatibility with Your Tankless Water Heater

Not all expansion tanks are created equal, and they don’t all work with every tankless water heater. Double-check the specs to make sure the tank you’re eyeing is a good match for your system.

Installation and Maintenance

Some expansion tanks are pretty straightforward to install—especially if they come with pre-installed fittings. Others might be a bit trickier and might even need a professional to get them set up. Also, think about maintenance. You’ll want to check the air pressure now and then and maybe replace the diaphragm after a few years.

Our Top Picks for the Best Tankless Water Heater Expansion Tanks

Let’s get into the nitty-gritty. Here are five expansion tanks that we think stand out from the rest:

Amtrol EX-30 Expansion Tank

The Amtrol EX-30 is a fan favorite for a reason. It’s built to last and does a great job managing the pressure from thermal expansion. With a 4.4-gallon capacity and a durable steel build, this tank is pre-pressurized to 12 psi and comes with a butyl/EPDM diaphragm. It’s easy to install, thanks to its pre-installed fittings, and it’s a solid choice for medium-sized systems. Just keep in mind that it’s a bit larger than some other models, so make sure you have the space for it.

Watts DET-5 Expansion Tank

If you’ve got a smaller system or limited space, the Watts DET-5 might be perfect for you. This compact tank holds 2 gallons and is pre-charged to 12 psi. Its steel construction and butyl diaphragm make it durable, and it’s easy to tuck away in tight spots. Plus, it’s easy on the wallet. The downside? Its smaller capacity might not be enough for larger systems.

Thermal Expansion Tank by Zurn Wilkins

The Zurn Wilkins expansion tank is super versatile and works well with a variety of tankless water heaters. It has a 4.5-gallon capacity and comes pre-charged to 20 psi. Made from heavy-duty steel, it’s built to handle the job. While it’s a bit pricier, you’re paying for top-notch quality and compatibility.

H2O Supply Thermal Expansion Tank

The H2O Supply tank is another great option for those tight on space. It’s a 2-gallon tank that comes pre-charged to 15 psi. Its steel construction and polypropylene liner make it durable, and its compact size makes it easy to install. Plus, it’s pretty affordable. Just remember, it’s not meant for larger systems, so it’s best for smaller setups.

A.O. Smith T-5 Expansion Tank

A.O. Smith is a name you can trust when it comes to water heaters, and their T-5 expansion tank lives up to the brand’s reputation. This 2-gallon tank is pre-charged to 12 psi and is made from high-strength steel with a corrosion-resistant lining. It’s easy to install and works with most tankless water heaters. The only downside is its limited capacity, which might not be ideal for larger systems.

Installing and Maintaining Your Expansion Tank

So you’ve picked out your expansion tank. Now what? Here’s a quick guide on getting it set up and keeping it in good shape.

Step-by-Step Installation

First, turn off the water supply to your tankless water heater. Then, drain any remaining water from the system to reduce the pressure. Next, attach the expansion tank to the cold water supply line using a T-fitting. Make sure the tank is oriented correctly with the air valve facing up. Before you turn the water back on, check the air pressure in the expansion tank. It should match your system’s water pressure. Adjust it if necessary using a hand pump. Once everything’s set, turn the water supply back on and check for leaks. Run some hot water through your system to make sure the tank is working as it should.

Regular Maintenance Tips

To keep your expansion tank in top shape, check the air pressure at least once a year. You’ll also want to inspect the tank for any signs of leaks or corrosion. If the diaphragm inside the tank starts to wear out, replace it to keep everything running smoothly.

Wrapping It Up

Choosing the right expansion tank for your tankless water heater isn’t just about making sure it works—it’s about keeping your home safe and extending the life of your system. We’ve checked out some top choices, and each one has its perks depending on what you need. Whether you’re after something small or something more robust, there’s an expansion tank that fits the bill. Plus, a bit of regular maintenance can make a big difference in keeping everything running smoothly.

Frequently Asked Questions (FAQs)

How can I tell if my expansion tank is doing its job?

You can test your expansion tank by pressing the Schrader valve (that’s the air valve on top). If water comes out instead of air, it’s time to replace the tank. Also, check if the air pressure matches your system’s water pressure.

Can an expansion tank help reduce that annoying water hammer noise?

Absolutely! An expansion tank can absorb the shock that causes water hammer, reducing noise and preventing damage to your pipes.

What should I do if I notice corrosion on my expansion tank?

If you spot corrosion, you’ll want to take care of it right away. Depending on how bad it is, you might be able to clean it up and apply a protective coating, or you might need to replace the tank altogether.

How often should I check the pressure in my expansion tank?

It’s a good idea to check the pressure at least once a year, or if you notice any changes in your water pressure.

Is it hard to install an expansion tank on my own?

If you’re handy, you might be able to install it yourself, especially if the tank comes with easy-to-use fittings. But if you’re unsure, it’s always a good idea to call in a pro to make sure everything’s set up correctly.