What Is a Water Heater Thermal Expansion Tank and Is It Necessary? – Fresh Water Systems

Water Heater

A water heater is often overlooked until it stops working. However, with the increasing concern for safety and updates to building codes, the necessity of expansion tanks for water heaters has become apparent. In this article, we will explore what water heater expansion tanks are, their importance, and how to determine if you need one.

What is a water heater expansion tank?

A water heater expansion tank, also known as a thermal expansion tank, is a small overflow tank that compensates for the thermal expansion of water inside a water heater. As the temperature of the water increases, it expands, resulting in increased pressure within the system. Without relief, this pressure can cause damage to valves, plumbing, or the water heater itself. Thermal expansion tanks solve this problem by accommodating the excess water that results from the increased pressure.

Do I need a thermal expansion tank for my water heater?

Expansion tanks are required by building codes in all new water heater installations in closed systems. A closed water system uses check valves or other devices to prevent water from being sucked back into the municipal water supply. Since homes are now required to have check valves to prevent backflow contamination, they have become closed-loop systems. Therefore, all new water heater installations must incorporate a thermal expansion tank.

If your current water heater does not have an expansion tank, adding one can benefit your system. High pressure in a water heater can lead to leaks, ruptures, and corrosion, which can be costly to repair. While an expansion tank is an additional cost, it can save you money in the long run by preventing these problems.

What size water heater expansion tank do I need?

The size of your water heater expansion tank should be based on the capacity of your tank and your home’s water pressure. The capacity of your water heater can be found on the tank’s exterior, and you can measure your home’s water pressure with a pressure gauge. Using these values, you can determine the appropriate size for your expansion tank.

It is generally recommended to stick to the following sizes for your expansion tank:

  • Water heater capacity up to 60 gallons:

    • Water pressure < 60 psi – 2-gallon expansion tank
    • Water pressure 60 psi or greater – 3.2-gallon expansion tank
  • Water heater capacity > 60 gallons:

    • Water pressure < 50 psi – 2-gallon expansion tank
    • Water pressure 50-60 psi – 3.2-gallon expansion tank
    • Water pressure > 60 psi – 4.4-gallon expansion tank

How much do water heater expansion tanks cost?

The overall cost of a water expansion tank installation, including the tank itself, averages a little over $200. The labor cost of installation can vary depending on the accessibility of your system and the size of the expansion tank being installed. While it is possible to install an expansion tank yourself, it is recommended to hire a professional to avoid additional costs due to incorrect installation.

How often do you need to replace a water heater expansion tank?

A thermal expansion tank will typically need to be replaced every five to ten years. To prolong its lifespan, it is important to ensure that the tank’s pressure matches the incoming water pressure. This helps preserve the bladder’s integrity and prevents valve leaks. Regardless of maintenance, an expansion tank will need replacement around the ten-year mark.

Advantages of water heater expansion tanks

Water heater expansion tanks offer numerous advantages to your plumbing system, which is why they are now required by building codes. These advantages include:

  • Preventing leaks caused by pressure buildup
  • Providing an additional layer of security alongside the water heater’s pressure relief valve
  • Saving money by preventing water damage or pipe bursts
  • Inexpensive to purchase and install
  • Occupying minimal space

Disadvantages of water heater expansion tanks

While water heater expansion tanks are highly advantageous, they do have a few disadvantages. These include:

  • Certain components are prone to failure
  • Small installation errors can cause problems within the system

However, with proper installation and calibration, a water heater expansion tank is a reliable safety feature. Even if it fails, the consequences are less severe and costly compared to failure within the plumbing system.

Water Heater Expansion Tank

How to test a water heater expansion tank

Water heater expansion tanks can easily fail, so it is important to test them if you suspect an issue within your system. There are a few simple tests you can perform to determine if your tank is functioning properly.

Tap the outside of the tank

Lightly tapping the exterior of the expansion tank with a metal object can give you an indication of any issues. In a properly functioning tank, you should hear different sounds when tapping the top and bottom. If the sounds are similar, the tank may not be filling as it should.

Observe water pressure

If you haven’t used hot water for an extended period, observe the water pressure when you next use hot water. If the water surges out faster than normal and then calms down shortly after, it indicates pressure buildup within the system, possibly due to a faulty expansion tank. While this method is not definitive, it serves as a warning sign that further investigation is necessary.

Check the air valve

All thermal expansion tanks have an air valve called the Schrader valve, which resembles a tire valve. Bleeding a small amount of air from the Schrader valve can determine if the tank is operating correctly. If air comes out, the tank is functioning properly. However, if water leaks from the valve, it indicates a rupture in the tank’s bladder, necessitating replacement.

Check the tank’s pressure

When a water heater expansion tank is installed, its pressure must match the incoming water pressure. The pressure within the tank should remain consistent throughout its lifespan. To check the pressure, use a pressure gauge on the Schrader valve, the same way you would check your car’s tire pressure. Adjust the pressure as needed to match your home’s water pressure.

If you have any additional questions or need assistance, feel free to contact us.

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