Does My Water Heater Need an Expansion Tank? (ALL States)

Expansion tanks are often the forgotten heroes of water heaters. It serves the important function of moderating the pressure within a water heater system. Determining if you need one for your home can be confusing, as laws across states are not consistent. Luckily, there are people like us who can help give you all the information you need!

If you have a closed water heater system, then you more than likely need an expansion tank. This is because your water heater needs extra space to contain the water when it heats up. If it does not have this space, the water heater could burst and cost a lot of money to repair. 

Knowing what to look for and how to determine if you need an expansion tank can be tricky for homeowners not familiar with the water heater system. This article will go over the basics of expansion tanks and include steps on how to install one on your own. So follow along to learn the basic information needed to take on an expansion tank project!

What is an Expansion Tank? 

As the water heats up, it expands in volume. This means if you have constricted space in your water heater there may not be enough area for the water to do this. The process can lead to increase pressure in your water heater. And if the water expands and has nowhere to go, it could lead to your water heater bursting.

Too much pressure is rarely a good thing, and expansion tanks help fix this issue. It gives your water heater the extra space it may need to allow water the space to expand. Now not all water heaters need this function, but it is especially crucial for closed water systems. As they only have a ‘closed’ amount of space where the water can go.

Expansion Tank

You may already have a water heater expansion tank connected to your heater. It is simply an extra compartment connected to the main water heater. It may look like a small propane tank that can hold between 2 and 4.5 gallons of water, depending on the needs of your water heater. 

Additionally, this tank is usually connected to the heater. This is because hot air and water rise and their temperatures increase, allowing the water to collect where it naturally goes. Expansion tanks are crucial to the overall function and safer of your water heater system.

When Do You Need an Expansion Tank? 

There are a few instances when you will need an expansion tank for your water heater. They mostly depend on the current system of your water heater. But sometimes it also depends on the functionality of the water heater or the laws of your state. Here is a quick rundown of all these scenarios!

If You Have a Closed System 

There are two main types of water heater systems, open-loop and closed-loop. With an open system, the excess water created in the heating process flows back into the main water line. Whereas with a closed system, the extra heat and pressure will cause the tank to expand as the water has nowhere to go.

This is why closed systems always need an expansion tank. The expansion and contracting of the water heater tank are not good for it. If you are lucky, the tank will simply grow distorted. But if you are unlucky, the pressure could make the tank crack or violently burst.

How Can You Tell If You Have a Closed System 

The best way to see if you have a closed water heater system, is to check for a pressure regulator or backflow prevention device. The purpose of this item is to regulate water flow if the tank becomes too full but does not work on the scale the expansion tank does. This item is a bell-shaped mechanism that could be located in a variety of locations.  

These regulators will be on the main water shutoff valve. The shut-off valve could be located on an outside wall, in a basement, or in a utility closet. Look for the water shut-off valve and see if it has this bell-shaped device attached to it. If you see that, then you definitely have a closed system.

If Your Water Pressure is Too High 

Even if you do not have a closed system, your water heater may not be well suited to run without an expansion tank. One way to examine this is to determine if the water pressure is too high. All kinds of water heater systems run the chance of having high water pressure, so it is important to take this into account.

Increased water pressure, particularly when the system is on, can lead to the same problems as a closed water system. This means you could be in need of an expansion tank for the safety of your home and water heater system. If you suspect this could be an issue you will want to gauge the psi of your water heater tank.

How To Tell What Your Water Pressure is 

It is pretty easy to tell what your water pressure is within your home’s plumbing system. Water pressure is measured by psi, or pounds per square inch, and all you will need is a pressure gauge. The ideal range for water pressure is between 50 and 60 psi.

You need to attach the gauge to a hose or faucet and turn on the water. Then it will be easy to read the psi and determine if you need an expansion tank. You will also want to take these measurements over a 24-hour period, in case a certain event affects a moment but not overall. 

It’s Legally Required 

Water heater expansion tanks are usually pretty much always required for closed systems, regardless of what state you are in. However, some buildings will have additional codes requiring this. So if you live in an apartment building you should check up on this. But if you do not have a closed system, you usually do not need to worry about legal requirements.

What States Legally Require An Expansion Tank? 

Practically every state requires an expansion tank on closed water heater systems. North Carolina, Oklahoma, California, Florida, and most of Texas all require these functions on water tanks. If you have an open system then the rules flex depending on counties or building regulations. 

There is no general consensus, but you should expect you need one for a closed system in a residential home. If you have an open system, then it is much less mandated seeing as there is less of a risk of dangerous pressure levels. Or if you have an on-demand water heater, there is less regulation on that system as well.

Legal requirements for this fixture vary across the states, but for closed systems, you certainly should have an expansion tank. All other systems vary in their regulation, but it is generally not necessary. If you are concerned it is best to reference your state or county codes for clarification.

How To Install An Expansion Tank 

You will be able to install an expansion tank on your own, but you must be certain about the different functions of the water heater unit. Picking out the correctly sized expansion tank will ensure you have enough space for the heating process. Additionally, you will need some tools listed here:

  • Pipe sealing tape
  • Pipe wrench
  • Appropriate water piping
  • Union nut
  • Plastic insulator
  • Solder adapter
  • Gasket
  • Union body
  • Propane torch
  • Thermal expansion tank
  • Pipe wrench or channel-lock pliers
  • (2) 3/4-inch copper female-threaded unions
  • 3/4-inch copper tee-fitting
  • 3/4-inch copper pipe
  • Additional 3/4-inch copper fittings (as needed)
  • Copper flex pipes (if needed)

Here is a small chart to see the size of tank you will need!

Water Heater CapacitySupply Pressure (psi) Expansion Tank Size
40 to 60-gallon40-50 psi2-gallon
40 to 60-gallon60-80 psi3.2-gallon
80-gallon40 psi2-gallon
80-gallon50-60 psi3.2-gallon
80-gallon80 psi4.4-gallon

Step 1: Attach a Dielectric Union 

First, you will wrap several layers of pipe sealing tape over the threads of the steel pipe. Then it is time to install the threaded end of the dielectric union body to the steel pipe. Use a pipe wrench to turn the union clockwise and tighten it.

Then you will need to slide the union nut over the end of the copper pipe with the open-threaded end facing out. Afterward, you will slide the orange color plastic insulator over the copper pipe.

Step 2: Attach Copper Adapter 

After you have set up the dielectric union, it is time to install the copper solder adapter. Do this by placing the adapter onto the copper pipe. Then you will sweat the solder adapter to the copper pipe using a propane torch to bind it.

Then you will attempt to set the plastic insulator as far away from the torch as you can. This way you avoid melting the insulator. Then it is time to wait a few minutes to allow the pipe to cool.

Step 3: Attach Tee Fitting 

Once the pipe is cool, you will grab the rubber gasket. Here you will place this piece between the union nut and the union body and assemble it.  Once that is used, you will use a pipe wrench to turn the union nut clockwise. Make sure this is secure.

At this point, you will need to inspect the connection to ensure it is watertight! You can push some water through it and see if it leaks. If you do have some leakage, go back and re-tighten the tee fitting.

Step 4: Attach Expansion Tank Pipe 

Now, using the torch again, attach a short length of horizontal copper pipe to the side outlet on the tee-fitting you just set up. The length of this pipe is dependent, but you will want to keep it as short as possible. Try to not make it longer than roughly 6 inches.

At the other end of this pipe, you will then attach a female threaded adapter. Again you can use the torch to bind these elements together!

Step 5: Attach the Expansion Tank 

Now it is time to finally attach the expansion tank to all the pieces you just set up! You will wrap some more pipe-sealing tape around the threaded fitting on the expansion tank. Then you will screw it onto the threaded adapter on the horizontal pipe. You can do this by hand and be sure to not over-tighten it so you do not damage the pipe.

To complete the installation you will then connect the top outlet on the tee-fitting to the cold water supply pipe using whatever fittings are necessary. A copper flex line tends to work best, but you can use rigid pips. Finally, connect the hot water pipe to the water heater, turn it on, and look for leaks!

How Much Does It Cost To Install An Expansion Tank 

Installing your expansion tank can cost different amounts depending on the materials you already have and what else you need to buy. The cheap 2 gallons version of the expansion tank cost around $40 while larger ones are around $200. However, there are the extra costs of construction materials as well!


If you need to buy all the construction materials yourself, plus the expansion tank, your costs will range between $60 and $300. This depends on the piping and tools you buy, plus the size of the tank you decide you need!

Hire a Professional

By hiring a professional plumber, you ensure the job is well done and the materials are exactly what is needed. If you are unsure about completing this project on your own, you should have a professional. This ensures personal safety and that the project is done right. This will generally cost you about $350 for small expansion tanks. If you are needing a larger tank, it will cost more.

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