Best Water Heater Expansion Tanks (2026): 5 Picks + How to Choose the Right Size

A water heater expansion tank helps protect your plumbing from pressure spikes caused by thermal expansion. As a result, it can reduce relief valve dripping, noisy pipes, and wear on fixtures—especially in homes with a closed system.

Water heater expansion tank: what it does (and why you might need one)

When water heats, it expands. In an open system, that extra volume can push back toward the supply. However, in a closed system (often created by a PRV, check valve, or backflow device), pressure can rise quickly and stress the water heater and connected fixtures.

For a helpful overview of water heating basics, see DOE:
https://www.energy.gov/energysaver/water-heating

If you want a pro to confirm your system type and install correctly, start here: Water Heater Services.

Water heater expansion tank: signs you may need one

You may benefit from an expansion tank if you notice:

• The T&P relief valve drips intermittently
• Pressure feels “spiky” or inconsistent
• You hear banging pipes after hot water runs
• You have a PRV or backflow device on the main line

Additionally, if whole-home pressure seems high or unstable, a PRV issue may be involved. In that case, start with Water Line Repair.

Water heater expansion tank sizing: how to choose the right size

Sizing is mainly about:

1. Water heater gallons
2. Static water pressure (PSI)
3. Whether you truly have a closed system

Step 1: Find static PSI

First, stop all water use. Then, check pressure at a hose bib with a gauge. Finally, write that PSI down.

Step 2: Match precharge to PSI

Next, set the expansion tank air precharge to match your home’s static PSI. Otherwise, the tank won’t accept expansion properly.

Step 3: Use a sizing chart (best practice)

Instead of guessing, use a proven chart. Amtrol’s sizing guide is a solid reference:
https://s3.supplyhouse.com/product_files/Amtrol%20-%20142-149%20-%20Sizing%20Guide.pdf

In general, many 40–50 gallon heaters pair with a smaller tank class, while larger heaters or higher PSI often need a bigger tank. Therefore, the chart is the safest way to avoid undersizing.

5 reliable picks (2026)

Choose the correct size class first, and then pick the brand/model you can service easily later.

1. Amtrol Therm-X-Trol (ST series)
2. Watts PLT series (PLT-5 / PLT-12)
3. A. O. Smith expansion tank (common 2-gallon class)
4. Everbilt thermal expansion tank (common 2-gallon class)
5. Rheem/Ruud expansion tank options (multiple size classes)

Water heater expansion tank install: what matters most

Even a correctly sized tank can underperform if the install is sloppy.

• First, set precharge correctly before pressurizing the system.
• Next, support the tank properly because it gets heavy when full.
• Additionally, place it where it’s serviceable (don’t bury it behind finished walls).
• Finally, confirm the real cause is thermal expansion—not a failing PRV or abnormal pressure.

If you suspect high pressure or a failing PRV, we can help through Water Line Repair.

Common mistakes to avoid

• Undersizing the tank (relief valve dripping continues)
• Skipping precharge adjustment (tank can’t accept volume)
• Hanging the tank unsupported
• Ignoring high pressure from a PRV issue

DIY vs call a pro

DIY may be reasonable if:

• You can safely shut off water/power
• You can measure PSI and adjust precharge
• You can mount and support the tank correctly

Call a pro if:

• You’ve had relief valve discharge, hammer, or pressure swings
• Shutoffs are old/corroded
• You want sizing done right the first time

Start here: Water Heater Services.

Service Area (Maryland only)

Quince Orchard Plumbing serves Gaithersburg (20878), Rockville, Germantown, North Potomac, Darnestown, Montgomery Village, Potomac (north), Derwood, Kentlands, and Washington Grove.