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Expansion Tank vs Pressure Tank: What are the Differences?

Scott Winfield
Last Updated on
by Scott Winfield

Most people often 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.

What Is an Expansion Tank?

An expansion tank is a smaller tank that is installed on the pipes above your home water heater system. The main work of this vessel is to help contain the water pressure resulting from the fact that water expands when is heated.

What Is an Expansion Tank?
What Is an Expansion Tank?

Without an expansion chamber, hot water in the heater would build up pressure. This pressure could cause damages to the plumbing system by affecting the pipes, valves, joints, or water heater.

Thermal expansion happens several times daily, depending on your home hot water use. The expansion occurs because water is non-compressible, so heating leads to an increase in the water volume.

The expansion tank absorbs the pressure, therefore, eliminating any stress on your plumbing system.

What Is a Pressure Tank?

A pressure tank refers to a fiberglass or metallic vessel connected to a home plumbing system that controls the water pressure. 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 the home at the correct pressure. It also contains compressed air, which is used to exert force on the water.

The water pump would keep turning on and off without a pressure tank. This effect would cause cycling problems, thereby shortening the pump’s lifespan.

Difference Between Expansion and Pressure Tank

The biggest difference is in their functionality when it comes to expansion tank vs pressure tank. There are other slight differences such as price, durability, and installation.

It is essential to understand these differences because it ensures that you purchase the suitable device for your intended function.

1. Functionality

A pressure tank and a expansion tank are similar in that they 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, heater, and other plumbing system parts. It works by holding steam and excess water released from the water heating process in the boiler.

This process helps remove excessive pressure from any plumbing fixtures connected to the heater.

On the other hand, a pressure tank works with a 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 the home.

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

Essentially, the pressure tank eliminates the need to turn the water pump on every time you need water in your home. Therefore, it lengthens the lifespan of the water pump, thus cutting down repair or replacement costs.

2. Durability

Durability is another essential point to consider when looking at expansion tanks vs pressure tanks. Generally, durability is critical for any water tank. You want it to serve you for as long as possible without any problems.

Typically, expansion tanks last longer than pressure tanks. On average, an expansion vessel lasts anywhere between 6 to 10 years with proper maintenance, thanks to the robust and sturdy material and design.

On the other hand, pressure tanks last anywhere between 5 to 7 years. During this time, the vessel will require little to no maintenance.

3. Cost

It is worth noting that the cost of either tank varies depending on the quality and capacity.

On average, residential expansion tanks cost anywhere between $40 and $200. Depending on the capacity and design, the price could soar up to $1000 for commercial expansion tanks.

In comparison to expansion tanks, pressure tanks are a bit more expensive. Typically, the price tag for a residential pressure vessel ranges between $50 to $650. This tag could go up to $1500 for commercial pressure tanks.

It is worth noting that the size of the pressure tank varies depending on the demand. Bigger homes, apartments, and commercial properties use large tanks.

This implies that the budget should be bigger to ensure the tank’s capacity to fill the water requirements.

4. Installation

Expansion tanks are easier to install than pressure tanks. The difference mainly comes due to the complexities involved with pressure tank systems.

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

It is essential to ensure that you work with a professional during installation. An expert understands the intricacies of installing these systems, which helps ensure that they function well.

It would be best if you also worked with an expert during any repairs or replacements to help boost the durability of these tanks.

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Will an Expansion Tank Increase Water Pressure?

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

This process helps safeguard your plumbing system from damages by thermal expansion. 

Is an Expansion Tank Really Necessary?

Yes, an expansion tank is necessary for your home plumbing system. The vessel helps take off 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.

It would 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. It improves the durability of the water heater and other piping fixtures around it.

Therefore, be sure to install an expansion chamber because it helps boost the durability of the water heater.

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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.

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