What Is A Boiler Expansion Tank?

image of a boiler expansion tank

Have you ever heard a loud booming sound when you switch off your shower? You might even have gotten scared that your water heater might explode. An HVAC technician might have also told you that you need a boiler expansion tank replacement but offered no other explanation. Don’t fret! This article will discuss what you need to know about boiler relief tanks.

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What Is A Boiler Expansion Tank?

A boiler expansion tank is a vital water heating system component. It is a small tank that is located at the top of the water boiler. Its job is to provide space for when the heated water expands. It has a diaphragm in the middle, and it is what separates the tank into two. One part is where the expanded water goes to. The other is an air cushion for the changes happening and to regulate the pressure buildup from the water heating process.

Older expansion tanks used to be a single-section unit only. The new design was to ensure that air does not enter the boiler and cause corrosion. Expansion tanks are helpful in the water heating and cooling processes. These tanks prevent some of the causes of water hammer or hydraulic shock.

Water Hammer Definition

image of a homeowner dealing with a water hammer

Also called hydraulic shock, water hammer is a common occurrence that can lead to worn out parts in your water heating equipment. If you’ve heard a loud bang when you switch off your bathtub or faucet, then the cause is likely because of the abrupt change in the water flow direction. This phenomenon can be annoying. It can also cause the pipes and the heating system to deteriorate faster. A boiler expansion tank can help prevent this issue as well as preserve your heating unit.

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Kinds Of Boiler Expansion Tanks

image of a boiler with expansion tank

The two different kinds of boiler expansion tanks are as follows:

Steel Type Expansion Tanks

This expansion tank model is typically seen in older homes. This has been used for decades and has no diaphragm. Therefore, the water and air touch each other, so corrosion needs to be avoided as much as possible. A steel type expansion tank is equipped with a sight glass. It is a small window that allows you to view the water-to-air ratio in the tank.

The right water to air ratio is dependent on different factors, including what material the convectors are made of and the amount of water the heating tank can hold. Some of the problems you might encounter with a steel type tank are tank flooding, malfunctioning gaskets, and corrosion. Call your local trusted tech to help you find the correct size of steel type expansion tank for your boiler.

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Bladder Type Expansion Tanks

On the other hand, this expansion tank model has a diaphragm. This feature allows bladder type expansion tanks to have longer-lasting capabilities. Although having the diaphragm means that the water and air are separated, the air inside the system is still not eradicated. The air should be removed from the tank. Seek professional help to determine how much pressure is allowed within your system. An HVAC expert can also help you find the correct bladder expansion tank size for your boiler tank.

Is Your Expansion Tank Working Properly?

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One of the most common reasons your expansion tank isn’t working correctly is incorrect chamber pressures. Steel expansion tanks are equipped with a pressure relief valve. Check it and see if it is venting hot water. This is an indication that the tank pressure is having an issue. Look through the sight glass to see if the pressure is off. If you have a bladder tank, you can check the pressure on the diaphragm’s air section to determine if there is a need to drain the water so that the tank can be refilled with air.

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Point Bay Service Van

Heating systems typically have one or more boiler expansion tanks. However, not all homeowners know for what purpose they are there. These tanks help with pressure regularization in your heating system during the boiler tank’s water heating process. It helps prevent a lot of boiler tank problems, including overpressurization and water hammer. This way, you help prolong your heating system’s lifespan. Contact Point Bay Fuel today and get a free installation quote!

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Call Point Bay Fuel For All Of Your HVAC Requirements


Point Bay Fuel provides superior heating and cooling services in Monmouth and Ocean Counties, New Jersey. Rest assured that we only hire highly-trained and professionally certified technicians. We conduct exceptional HVAC services, such as boiler installation, furnace replacement, AC maintenance, and ductless repairs. Each of our friendly techs is skilled, knowledgeable, and experienced in conducting accurate and prompt repairs.

Our company offers affordable and the most competitive HVAC service rates in the area. We provide maintenance services to improve your home’s comfort, energy efficiency, and cost-effectiveness. If you need a replacement system, we can recommend the best make and model for your home and budget. Your satisfaction is our priority, so all our works come with a guarantee. Schedule a service appointment with Point Bay Fuel today. We offer free, in-home estimates.

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