Expansion Tank vs Pressure Tank: What’s The Difference?

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Pressure tanks and expansion tanks have similar designs and might sound similar, but they’re not quite the same.

In this guide, we’ve outlined the main differences between an expansion tank vs pressure tank, so you can choose the right tank for you.

📌 Key Takeaways:

  • A pressure tank is a large tank that stores water, usually from a private source like a well, under pressure, so that it can be delivered instantly around your home when you need it.
  • An expansion tank, otherwise called a diaphragm tank, is a smaller tank that protects your hot water heater and plumbing system from thermal expansion.
  • Pressure tanks are larger than expansion tanks and come in several designs – they don’t always have a bladder or a diaphragm.

⚖️ What’s The Difference Between an Expansion Tank and a Pressure Tank?

The main difference between an expansion tank and a pressure tank is that an expansion tank has a diaphragm or bladder and is designed to relieve water pressure in a hot water heater system, while a pressure tank doesn’t always have a bladder (there are a few different designs) and is designed to store water under pressure and deliver it at the required flow rate around your plumbing system.

Expansion tanks don’t increase water pressure – they relieve water pressure in your water heater and plumbing system. Pressure tanks do increase water pressure and ensure a consistent supply of water to your home.

What is a Pressure Tank?

A pressure tank is a tank made from fiberglass or metal that controls the water pressure in your home’s plumbing system. The key purpose of a pressure tank is to ensure your home’s water pressure remains constant, so you can enjoy a steady flow of water at all times.

Pressure tanks hold water that has been pumped from the well. When you switch on a faucet or a water-using appliance, the tank delivers water at the correct pressure into your plumbing.

Water pressure can be maintained because the tank contains compressed air. The exact pressure inside the tank at any given time depends on how much water it contains.

well pressure tank in basement

What is an Expansion Tank?

An expansion tank is a small tank that’s designed to prevent excessive water pressure in your hot water heating system. Hot water increases water pressure, and these pressure fluctuations can damage the heater’s plumbing components (including the water pipes and pressure relief valve). You can alleviate this excessive pressure by installing an expansion tank.

Expansion tanks have two sections, which are divided by a rubber diaphragm. One section contains water and is connected to your heating pipes, while the other contains compressed air. The diaphragm is pushed down as hot water enters the heating system and pressure increases, making the air in the tank more compressed and giving water more room. As a result, the water takes up less space in the heating system and excess water pressure can be avoided.

You should consider installing an expansion tank if you want to maintain the efficiency and longevity of your hot and cold water heating systems.

Expansion tank installed in basement

🆚 Expansion Tank Vs Pressure Tank: Key Differences

There are a few key differences between expansion tanks and pressure tanks that you should be aware of:


Pressure tanks and expansion tanks have completely different purposes and can’t be used interchangeably.

A pressure tank’s purpose is to deliver water at the required pressure around your home. This tank is usually installed after a well water pump to avoid the pressure rise and fall if you were to pump water straight from the well, and to prevent wear to the pump due to constant pump cycles.

By storing a large volume of water under pressure, a pressure tank can send water to your faucets and appliances as soon as you switch them on, with no need to wait for this water to be pumped up from your well.

The purpose of an expansion tank, on the other hand, is to mitigate thermal expansion as hot water enters your water heater and associated pipes and plumbing. This tank is installed somewhere near your water heater and prevents excess pressure that could damage your heating system.

By temporarily holding hot water, an expansion tank prevents a buildup of pressure inside your plumbing system and heater. Expansion tanks are an alternative to thermal expansion relief valves.

Installing an expansion tank next to a water heater


The functionality of a pressure tank and an expansion tank is similar: they’re both used to control water pressure, which protects plumbing fixtures. However, the process of performing these functions is different in each tank setup.

An expansion tank works by holding excess water and steam that escapes from the boiler when water is heated. The tank contains a diaphragm or balloon (which is why it’s sometimes known as a diaphragm tank), and this is pushed down as the tank fills with water.

A pressure tank works by storing water temporarily, like a reservoir would, when it is pumped into the plumbing system by a water pump. The tank uses pressurized air to store the water at the right pressure to deliver it instantly around the home when it’s needed. This relieves stress on the pump by supplying water even when the water pump is off.

Installation & Maintenance

Installing an expansion tank is easier than installing a pressure tank. This is because expansion diaphragm tanks aren’t as complex or as big as pressure tanks.

So, it also costs more money to install a pressure tank compared to an expansion tank.

Regardless, you should hire a professional to install any of these systems, since they play such an important role, and a poor installation could cause leaks and pressure issues throughout your home.

Both tanks require similar maintenance, but pressure tanks typically need more maintenance than expansion tanks.

To maintain a pressure tank, remove the cap over the air valve and check the air pressure with a tire gauge. It should be 2 PSI lower than the well pump’s cut-in pressure. Add or release air to achieve this pressure reading if needed. If the pressure is still low, the system may have a leak and needs replacing.

To maintain an expansion tank, check the tank periodically by placing your hand on the tank and feeling its temperature. The base of the tank should be room-temperature and the top of the tank should be warm. If the whole tank is hot, it suggests the diaphragm has failed, which can happen after a few years.

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

Expansion Tank Installation


Pressure tanks are bigger and more expensive than expansion bladder tanks, although price varies for both tanks depending on their capacity and quality.

Expect to spend between $50 and $700 on a pressure tank for residential use. The cost of a commercial pressure tank is even more expensive: up to $1,500.

A thermal expansion tank for residential use is around $50-$200. If you need an expansion tank for commercial use, you might pay as much as $1,000.

Your property size determines the size of the tank you will need in both scenarios. If you have a bigger home with more bathrooms and a greater daily water need, a larger tank will be needed, which will cost more money.


Pressure tanks and expansion tanks are both durable, but you can expect a water expansion tank to last longer than a pressure tank.

Pressure tanks have an average lifespan of 5-7 years without needing much maintenance.

Expansion tanks for water heaters have a 6-10 year average lifespan thanks to their sturdy design.

Durability depends on the quality of the tank you choose, so if you want your tank to last as long as possible with few repairs or problems, don’t buy the cheapest tank available.

expansion tank vs pressure tank

📑 Final Word

Many people confuse pressure tanks with water expansion tanks because of their similar names and functionalities. But you don’t want to buy the wrong tank by mistake, since they can’t be used interchangeably.

Before you spend your money, make sure you know which tank you need, and for what purpose.

If you’re still not sure, ask a plumber to advise you on your purchase. They can tell you what type of tank you need and offer recommendations on the best tanks for your requirements.

  • Jennifer Byrd
    Water Treatment Specialist

    For 20+ years, Jennifer has championed clean water. From navigating operations to leading sales, she's tackled diverse industry challenges. Now, at Redbird Water, she crafts personalized solutions for homes, businesses, and factories. A past Chamber President and industry advocate, Jennifer leverages her expertise in cutting-edge filtration and custom design to transform water concerns into crystal-clear solutions.

2 thoughts on “Expansion Tank vs Pressure Tank: What’s The Difference?”

  1. Avatar for Jennifer Byrd
    Victoria Addington

    I have chosen to look into methods that I may assist my aunt because she recently had a water well put on her property. It’s fortunate that I came across your article because you mentioned that the main goal of a pressure tank is to maintain a continuous water pressure in your home. Installing one seems like a smart idea because it may guarantee that you always have a consistent supply of water.

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