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Expansion Tank vs Pressure Tank: What are the Differences?

Scott Winfield
Written by Scott Winfield
Last Updated on

Most people confuse pressure tanks with expansion tanks, but these two tanks are different and they perform distinct functions.

Since both are essential for your home plumbing system, you need to understand their differences. So, let’s explain what both these tanks are, what they do, and in what ways they are different.

What is an Expansion Tank?

An expansion tank is a smaller tank that is installed on the pipes above your home water heater system. It helps contain the water pressure that’s produced by heat.

Since water, or any liquid for that matter, is a non-compressible matter, heat will inevitably lead to an increase in its volume. Without an expansion chamber, hot water in the heater would build up pressure inside the heater system itself.

Such pressure may cause damage to the plumbing system by affecting the pipes, valves, joints, or the water heater itself. Thermal expansion occurs several times on any given day, depending on your hot water use, so you can imagine how strenuous it can be for your pipes and water heater.

Thankfully, expansion tanks absorb that pressure, eliminating any stress on your plumbing system.

What is a Pressure Tank?

Pressure tank refers to a fiberglass or metallic vessel connected to a home plumbing system that controls the water pressure, and is mostly used to control the flow of well water. It helps maintain water pressure at a constant level and provides a steady flow of water into your home when the pump is turned off.

Pressure Tank
Pressure Tank

Essentially, the pressure tank holds water sourced from a well and delivers it to your home at the correct pressure. It also contains compressed air, which is used to exert force on the water.

Without a pressure tank, the well pump would keep turning on and off whenever you want to use water in your household. Such frequent pumping cycles cause the well pump to wear off quite easily and shorten its lifespan. So, installing a pressure tank can easily prolong the lifetime of the pump.

Difference Between Expansion and Pressure Tank

The main difference between expansion tank and pressure tank is that expansion tank controls the water pressure generated by heat from a water heater system, while pressure tank regulates the water pressure for a home well water system.

1. Functionality

A pressure tank and an expansion tank are similar in that both help protect plumbing fixtures by controlling the water pressure. However, there are some differences in where and how they carry out these functions.

An expansion vessel helps contain thermal expansion to protect valves, pipes, joints, the heater, and other plumbing system parts. It works by holding the steam and excess water released from the water heating process in the boiler.

A pressure tank, on the other hand, works with the water pump and acts as a reservoir. Therefore, it stores water, which is later pumped into your home through pressurized air.

The tank does this by detecting water pressure. When the pressure is low, it automatically takes on the role of supplying water to your home.

This functionality ensures that there is a constant water supply even when the pump is off.

Essentially, pressure tanks eliminate the need to turn the water pump on whenever you need water in your home. Therefore, they lengthen the lifespan of the water pump, cutting down repair or replacement costs.

2. Durability

Durability is also something you want to consider when looking at expansion and pressure tanks. Generally, durability is critical for any water tank, as you want it to serve you for as long as possible without any problems.

Typically, expansion tanks last longer than pressure tanks. On average, they may last anywhere between 6 to 10 years with proper maintenance, thanks to their sturdy and robust build and design.

Pressure tanks, on the other hand, last anywhere between 5 to 7 years. During this time, the vessel will require little care from you as long as you do basic pressure tank maintenance.

3. Cost

It’s worth noting that the cost of either type of tank varies depending on the quality and capacity of your specific product.

On average, residential expansion tanks cost anywhere between $90 and $350. Depending on their capacity and design, the price could go as high as $1000 for commercial expansion tanks.

In comparison to expansion tanks, pressure tanks are a bit more expensive. Typically, the price for a residential pressure vessel ranges between $100 to $650. This price could go up to $1500 for commercial pressure tanks.

4. Installation Requirements

Expansion tanks are easier to install than pressure tanks. The difference in installation difficulty is mainly due to the complexities involved with pressure tank systems, such as pressure switch settings and valves.

As such, a pressure bladder system has a higher installation cost than an expansion tank.

That aside, the installation process for both these tanks requires a lot of tools like wrenches, pressure gauges, drills, connectors, pipes, and, sometimes, specific installation kits. So, unless you are experienced in plumbing, it would be best to hire professionals for the installation, repair, or replacement of both types of tanks.

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Will an Expansion Tank Increase Water Pressure?

No, an expansion tank does not increase water pressure. The expansion tank handles thermal expansion from the heating process, thus reducing excessive water pressure.

This process safeguards your plumbing system from damage.

Is an Expansion Tank Really Necessary?

Yes, an expansion tank is necessary for your home plumbing system. The vessel helps bring down any extra water pressure caused by thermal expansion from the heater and other plumbing fixtures.

Without an expansion tank, the thermal expansion would create excess water pressure. This excessive pressure would be directed towards the heater’s walls, adjacent pipes, valves, and faucets, which would then create tension and ultimately cause leakages or bursts in the plumbing system.

So, the expansion tank is essential because it relieves the thermal expansion, thereby protecting the plumbing system. Additionally, it improves the durability of the water heater and the other piping fixtures around it.


Although both deal with pressure, expansion and pressure tanks serve distinct purposes. 

The former prevents the thermal pressure produced by water heaters from damaging the plumbing system of your household. The latter, on the other hand, maintains water pressure and stores water so that your well pump doesn’t work overtime and wear out sooner rather than later.

This difference in function also has an effect on the durability, price, and installation of these types of tanks. Since expansion tanks are just preventive devices that don’t need to maintain or control the water flow, they’re less complicated. So, they’re more durable, affordable, and easier to install when compared to pressure tanks.

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Scott Winfield
Scott Winfield
My name is Scott Winfield and researching and writing about water filters and other strategies to purify water has become my full time passion in recent years. I'm glad that you found our site and you can look forward to authoritative and well researched content here to help you get the best in water.
  1. Well water supply, and I have a pressure tank. Replacing a very old gas water heater with a high-efficiency electric water heater. Never had an expansion tank before. Do I need a pressure tank and an expansion tank? Or is the pressure tank enough?

    1. Hi Aaron, the general answer is that a tankless water heater means you don’t need an expansion tank. That said, details always matter and you need to consider your overall plumbing system in your house and I would recommend this article that references the International Plumbing Code to understand exceptions when you have special things going on in your home system, such as storage tanks and recirculating water systems.

  2. I really enjoyed reading your blog post comparing expansion tanks and pressure tanks for well systems. It’s fascinating to learn about the different functions and benefits of each type of tank. Your explanation of how expansion tanks help regulate water pressure and prevent damage to the well system was very insightful. I also appreciate how you highlighted the importance of proper sizing and installation for both types of tanks. It’s clear that you have a deep understanding of well systems and water management. Thank you for sharing this valuable information with your readers. Keep up the great work!

  3. My well system has a Flexcon Ind. Potable Water Expansion Tank 2.1 g 40PSIG max pres 150 PSIG. Its worked great for 20yrs and the set up does not include a Pressure Tank.
    How is this possible? There is a standard 90gal water heater. I need to replace the expansion tank but, after reading your article about tanks I’m confused.

    1. Hi William, not all well water systems have a pressure tank. I don’t know your system setup, but a pressure tank serves the purpose to provide consistent water pressure. So, it could be that it was never part of the system that was designed for you.

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