What Is A Boiler Expansion Tank?

boiler and boiler expansion tank

Have you worried about your water heater’s condition before? It can be because you hear a loud noise every time you turn off the shower. Maybe an HVAC expert advised you that it’s time to replace your boiler expansion tank, but you don’t know what this tank is or what it’s for. The boiler expansion tank is a crucial element of your home’s hydronic heating system or water heating system.

Read on to learn everything you need to know about boiler expansion tanks.

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What Is A Boiler Expansion Tank?

A boiler expansion tank is a small tank sitting on top of your water boiler’s main water tank. Water expands when it is heated, and this small tank is where water escapes to. A diaphragm sits in the middle of an expansion tank. This component separates the tank into two sections. One acts as the air cushion, accommodating the changes and regulating the pressure building from the heated water. The other is where the expanding water escapes.

Expansion tanks used to only have a single section. However, its design was improved, and it now has two sections so that air does not enter the boiler and cause it to corrode. Expansion tanks help in the cooling or heating water processes. They are also beneficial in removing a few of the reasons behind water hammers or hydraulic shock. Below are things you need to know about water hammer and its symptoms.

What Is A Water Hammer?

Water hammer, otherwise known as hydraulic shock, is a common occurrence that results in water heater wear and tear. You might have noticed loud bangs whenever you switch the faucet or bathtub off. This noise is because the water flow changed direction suddenly, sending out shock waves in the process. As a result, the piping and heating system can get damaged and the sound, itself, is very annoying. Install a boiler water tank to prevent these issues and help keep your heating system in good working condition.

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Kinds Of Boiler Expansion Tanks

The two different boiler expansion tank models are steel type and bladder type. Take a closer look at them below.

Steel Type Expansion Tanks


Steel-type expansion tanks have been used for decades. As such, they are often found in older homes. This model is not equipped with a diaphragm, so the air and water touch. Therefore, using a steel tank is to prevent corrosion as much as possible. This type of tank has a sight glass, a small window that allows you to view the water to air ratio in the tank.

The right water to air ratio relies on several factors, including the material the convectors are made of (typically copper or iron) and the amount of water the tank can hold. Some issues of using steel tanks are due to air and water mixing. Examples of these problems are corrosion, malfunctioning gaskets, and tank flooding. A professional can assist you with finding the correct size of steel type expansion for your water boiler/heater.

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Bladder Type Expansion Tanks

The most crucial difference between a bladder tank and a steel tank is that the former has a diaphragm. This means it has a component within the tank that separates the air and water. Therefore, they tend to last longer, but it doesn’t remove the issue of air in the system completely. A heating system that has a bladder expansion tank means that the air separates from the water and needs to be removed from the system. Ask a professional to help you ensure that the boiler tank has the right size of the bladder expansion tank.

Is Your Expansion Tank Working Properly?

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Are you sure that your expansion tank is working properly? A prevalent cause of expansion tank malfunction is incorrect pressures within the chambers. Steel expansion tanks come with a pressure relief valve. If they are venting hot water, it could signify that there is a problem with the pressures within the tank. Use the sight glass to check the water level to see if the pressure is off. If you have a bladder tank, check the pressure via the diaphragm’s airside. This will help you determine if the lines need to be drained of water to allow the bladder to be refilled with air.

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Most heating systems are equipped with one or more boiler expansion tanks. Unfortunately, only a few people understand their use. These small reservoirs and their systems help in the heating system’s pressure regulation when water is heated in the boiler tank. Thus, they ensure that boiler tank problems, like overpressurization and water hammer, do not happen. They also help preserve your heating system so you can use it for a long time. Call R.F. Ohl today to receive a free installation estimate.

Call R.F. Ohl For All Of Your Heating System Requirements

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When you need high-quality, affordable heating oil delivery services throughout northeastern Pennsylvania, make sure to call R.F. Ohl. All of our discount oil deliveries are fast and reliable while keeping your safety in mind. We also offer HVAC services, including maintenance, installations, repairs, and replacements. Each of our friendly techs is equipped with experience and knowledge to work on your HVAC system correctly. Book your next oil delivery or service appointment by calling R.F. Ohl today. We offer free, in-home estimates.

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