Water Heater Expansion Tank

Best Water Heater Expansion Tank for Your Plumbing System

Ian Mutuli
Updated on
Ian Mutuli

Ian Mutuli

Founder and Managing Editor of Archute. He is also a graduate architect from The University of Nairobi, Kenya.
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What is An Expansion Tank?

Also called thermal expansion tank, a water heater expansion tank is a safety device that's designed to protect your household plumbing system from the thermal expansion that's caused when heating the water coming in. The risk of pressure damage from temperature rise is not a concern when dealing with a tankless water heater. However, you need an expansion tank if you own a tanked heater; otherwise, your plumbing system is at high risk.

This small tank absorbs cold water into its rubber bladder to reduce the excess heated pressure by your water heater. When both are sized and installed correctly, it will absorb the extra cold water into its bladder to minimize that excess pressure created in the water heating unit. Ultimately, expansion tanks help reduce water hammer issues and help protect you from high water bills, unnecessary damage, stress on your plumbing fixtures, and a more efficient and longer tank life.

Why Do You Need an Expansion Tank?

Cold water will expand once it's heated, the excess pressure that builds up inside the water heater tank will need to be released. Previously, the expanding water turned pressure in the tank would simply drain back out into the city water supply it came from. However, now the city water supply main is designed using backflow prevention devices, preventing the backward release of the pressure build-up.

This is known as backflow and uses a one-way valve. The one-way valve (check valve) prevents wastewater from inside your house from returning to the main water supply and contaminating the fresh water supply.

The water heater expansion tank is attached to the water supply pipe of the water heater to prevent excessive water pressure. If the pressure goes too high, it can damage the valves in the plumbing fixtures, the joints in supply pipes, and the water heater itself.

When is A Water Heater Expansion Tank Required?

This is highly recommended if your house has a ‘closed-loop system’ caused by any check valve or pressure regulating valve installed on your water supply line. A common illustration to compare to your closed plumbing system having high water pressure is like having high blood pressure. It normally doesn’t have immediate negative effects on your closed water supply systems, but, in the long run, there's wear and tear from the excess pressure that then reduces the life span of your whole plumbing system.

Is Water Heater Expansion Tank Necessary?

1. Amtrol ST-12 Thermal Expansion Tank

Amtrol ST-12 Thermal Expansion Tank
  • Eliminates the waste of energy and water, thus saving money
  • Prevents the relief valve from going off
  • Protects the water heater and plumbing fixtures from premauture...
  • Eliminates the waste of energy and water, thus saving money
  • Prevents a dangerous pressure build-up in the system

Amtrol is a reputable brand that deals with a range of water heater expansion tanks and accessories. The Amtrol ST-12 Thermal Expansion tank is affordable and a high-quality expansion tank that makes it to the top spot as the best water heater expansion tank available in the market.

Installation is easy and is compatible for use with most standard-sized water heaters in the market. Ultimately, this expansion tank helps to reduce the amount of water and energy that'd often go to waste while using a traditional water heater. In addition, when installed, it reduces the amount of pressure-volume that builds up in hot water heater tanks and the rest of a closed system, which helps extend the life of your fixtures, plumbing, and appliances.

Additionally, this expansion tank helps to reduce the amount of build-up that often occurs in various parts of your plumbing closed system that can, in the long run, cause a wide range of issues. The Amtrol ST-12 Thermal Expansion tank is a 4.4-gallon tank that also works with modern plumbing codes and enhances the prevention of backflow in a closed system.

It can also help increase the amount of heated water flow that's usable by returning the water that was held to the overall system when your main tank runs low on volume. Not only does it help reduce the overall waste of water and energy, but it also allows you to get more heated water out of the system, more than you would without this expansion tank.

Key Specifications:

  • 4.4 gallons
  • 2.2 pounds


  • Very affordable
  • Compatible with most standard-sized hot water heater tanks
  • It can be easily installed
  • Reduces the overall amount of pressure that might build up in the plumbing system
  • Overall it reduces water and energy waste
  • Reduces build-up in water heater
  • Meets requirements of the modern plumbing codes


  • Doesn't work for larger homes with more than 50-gallons

2. Falcon Stainless EXPT-2 Thermal Potable Water Heater Expansion Tank

Falcon Stainless EXPT-2 Thermal Potable Water Expansion...
  • Stainless Steel water connection to reduce corrosion.
  • 16 gauge solid steel tank, finished with highest quality urothane...
  • Steel clench ring regulates movement and prevents diaphragm from...
  • 100% Pressure tested and backed with a 5 year limited warranty.
  • Falcon Stainless E.T. series thermal expansion tanks 100%...

Falcon Stainless is also another trusted brand that's well-known for its range of home plumbing and water heater supplies, expansion tanks, and accessories. The Falcon Stainless EXPT-2 water heater expansion tank is high in quality, durably constructed, and affordable.

It is made from a 16 gauge stainless steel with a urethane paint finish, which helps reduce the corrosion and wearing out for chipping that mostly is what reduces the life of an expansion tank. This tank can be suitably used with standard-sized water heaters that are up to 50-gallons.

It comes in a diaphragm-style system with a butyl bladder and a polypropylene liner for it to operate much better and increase its lifespan. This unit also comes with a steel clench ring that helps with regular movement and helps prevent it from pressing onto the tank wall when it is full of heated water.

This tank has undergone a full pressure test subject to safety and functionality. Installation and operation are easy. You can be assured of its long lifespan since the purchase also comes with a 5-year limited warranty.

Key Specifications:

  • 2.1 gallon
  • 4.9 pounds


  • Compatible with hot water heater tanks that go up to 50-gallons
  • Comes in a diaphragm-style system
  • Constructed using 16 gauge steel to reduce chipping and corrosion
  • Steel clench ring that keeps it in place
  • Full pressure test
  • It can be easily installed


  • Doesn't work for larger homes with more than 50-gallons

3. Watts 4.5-gallon Expansion Tank

Watts 4.5 G Potable Expansion Tank for 50-Gallon Water...
  • For use with all types of direct-fired water heaters.
  • Controls thermal expansion of water in open domestic hot water...
  • Keeps system pressure below relief setting of relief valve.
  • Contains a durable membrane to prevent contact of water with air...
  • Rugged butyl diaphragm.

Watts is another reputable company that's best known for its wide range of plumbing-related equipment and accessories. Their product line includes pipe fittings, the check valve, and water heater expansion tanks.

This is a 4.5-gallon expansion tank that's well-constructed, versatile, durable, and affordable. Its large capacity works well with water heaters tanks that go up to 50-gallons. You can also use it with any type of direct-fired water heater, including most traditional systems.

The tank controls the amount of thermal expansion in your hot water system, thereby reducing the amount of building up in your hot water heater tank and other parts of the plumb system. It comes in a diaphragm body made from butyl that lasts long.

The Watts 4.5-gallon tank also has a durable membrane that largely makes up the tank to separate the excess water from its air cushion. It also has a system that's designed to keep the water below 80 psi. Anything above this might actually damage your plumbing and fixture system and shortening its lifespan. Installation is easy and overall helps reduce the amount of water and energy wasted by a water heater.

Key Specifications:

  • 4.5 gallons
  • 8.78 pounds


  • Compatible with water heaters that are up to 50-gallons
  • Durable construction
  • Automatically controls thermal expansion
  • Built-in a diaphragm system
  • Easy installation
  • Overall reduction in energy and water waste


  • Works best with smaller water heater tanks

4. Amtrol ST-5 Thermal Expansion Tank

AMTROL ST-5 Thermal Expansion Tank
  • Accepts expanded water caused by thermal expansion
  • Returns water to the system when hot water is used
  • Prevents the relief valve from going off
  • Inline thermal expansion tank
  • Accepts expanded water caused by thermal expansion

Amtrol ST-5 water heater expansion tank is an excellent option for smaller homes or households with a hot water heater that's less than 50-gallons in size. It uses a bladder-style expansion vessel constructed from high-quality stainless steel for durability and to reduce corrosion.

It returns water to the hot water system when the main tank runs low or even when hot water is being used. Additionally, the unit prevents the relief valve from going off and causing any issues. Installation is easy, and it can be installed either horizontally or vertically.

This tank is also lightweight and works to reduce any pressure that's built up, and helps reduce water and energy wastage. Lastly, it comes with a 5-year limited warranty.

Key Specifications:

  • 2 gallons
  • 4.6 pounds


  • Works great for smaller homes and water heaters that are up to 50-gallons
  • Constructed using stainless steel for durability and reduction of corrosion
  • Made in the USA
  • Returns hot water back into the system
  • Easy installation
  • It can be installed either vertically or horizontally
  • Reduces wastage of water and energy
  • Limited 5-year warranty


  • It is not built for larger homes and water heater tanks that are more than 50-gallons

5. Amtrol 7.4-gallon Expansion Tank

Amtrol 60 Extrol Boiler System Expansion Tank, 7.4 gal...
  • 1/2 nptm connection
  • 2.5 gallon max. Acceptance
  • 100 psig maximum working pressure

This 7.4-gallon expansion tank from Amtrol is an affordable, high-quality choice for larger homes and people who have a hot water heater that's larger than 50-gallons. Its diaphragm system helps reduce energy and water wastage while also reducing the built-up pressure that can be experienced in closed systems. In addition, it is well-constructed using great materials that help reduce corrosion while also increasing the lifespan of your fixture system.

It is easy to install and comes with a limited 5-year warranty.

Key Specifications:

  • 7.4 gallons
  • 4 pounds


  • Compatible with water heaters that are over 50-gallons
  • Works best for larger homes and bigger water heaters that are over 50-gallons
  • Diaphragm body system
  • Made from corrosion-resistant materials
  • Easy installation
  • Limited 5-year limited


  • Its a lot for smaller homes and water tanks

What to Consider for the Best Water Heater Expansion Tank?

A) What’s Your Water Heater Capacity?

You can get this information on the factory label that's attached to the water heater.

B) What’s Your House Water Pressure?

Measured in PSI (Pounds per Square Inch), the water pressure of your home's water supply can be easily measured using a gauge. Simply attach the gauge to a faucet or hose and turn on the water supply. It's best to check your water pressure on a 24-hour period. Alternatively, you can contact your water supply company.

C) How to Install an Expansion Tank?

  • First, determine your household's water pressure using a gauge. If the water supply is above 80 psi, you will need to install a pressure-reducing valve
  • Using a tire gauge, check the air pressure on the heating expansion tank
  • Using a hand pump, adjust the air pressure on your expansion tank to match the maximum water pressure of your house. Don't use an air compressor for this
  • On the cold water line, install the water heater expansion tank
  • Open one of the faucets and let it run until you have a steady stream of water to help remove any air that may be trapped within the tank

Frequently Asked Questions on the Best Water Heater Expansion Tank

1. Do you need multiple thermal expansion tanks for multiple water heaters?

Overall, to prevent damage, you need an expansion tank solution that's adequately sized for the plumbing system you have installed. For instance, a 50-gallon water heater can be served by a 2-gallon thermal expansion tank.

Having more than one heater in the same or connected system means that you can either have multiple thermal expansion tanks for each heater or one large expansion tank that can take all the incoming water supply pressure. Additionally, always check with a licensed plumber whether this is viable according to the local plumbing code amendments and the expansion tank manufacturer’s specifications to determine whether you're working with what's right for you.

2. What happens if my water tank heater is not connected to an expansion tank?

Most homes with a pressure-reducing valve on the city water supply main don't have an expansion tank since it wasn’t really required until recently. This may have caused excessive and high-pressure buildup, depending on the house's specific plumbing design.

Suppose you notice that the washers in the plumbing fixtures are rapidly deteriorating or a water leak from the water heater's relief valve, then you probably need an expansion tank. However, the plumbing services and installation will be much less than the cost you might incur when you damage your home’s plumbing system.

3. How long do thermal expansion tanks last?

On average, your water heater expansion tank can last roughly 5-10 years. To extend its life, make sure that your home's water volume pressure matches the air pressure of the expansion tank installed.

4. What happens in an expansion tank failure?

Failure will cause the extra pressure will cause a loss in the air cushion in the expansion tank, meaning that at each heating cycle, the excess water volume pressure causes stress on the temperature/pressure relief valve, which will then leak.

5. Is it better to get a bigger expansion tank?

Getting the right sized thermal expansion tank installed is important, but if you're ever in doubt, it's best to get a larger one than a smaller one. Getting a larger expansion tank for your house system will safely handle the extra water volume heating.

Ian Mutuli

About the author

Ian Mutuli

Founder and Managing Editor of Archute. He is also a graduate architect from The University of Nairobi, Kenya.