Nicolette Forbes

By: Nicolette Forbes on August 5th, 2022

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How to Install an Expansion Tank

Standard Water Heaters | Tankless Water Heaters

Having an expansion tank installed in your home for your water heater is part of the Los Angeles city code. But do you know what an expansion tank is and want to know how to install it?

At Monkey Wrench Plumbing, Heating & Air, we have worked all over the greater LA area, and have seen some bizarre or potentially dangerous installations of expansion tanks. So we have made this article so that you fully understand how an expansion tank is installed properly. 

In this article, we will discuss what an expansion tank is, how it works, how an expansion tank is installed, and ways to check if the tank is working properly.

While installing an expansion tank can seem like a daunting task, it does not have to be. By the end of this article, you will become experts in the basics of installing an expansion tank.


What is an Expansion Tank?

An expansion tank is another small tank attached to the water supply pipe of the water heater that helps alleviate pressure. This pressure is caused by thermal expansion (or the process of water expanding due to it being heated) that happens when water is being heated by your water heater. If the water pressure gets too high, it can damage valves in plumbing fixtures, supply pipes, and the water heater itself.

This extra tank is also a safety feature for your water heater, as, without an expansion tank, it can cause excessive scale or residue buildup, which leads to blockage problems with your plumbing system.

An expansion tank on a tank-style water heater.

There are also three different types of expansion tanks: 

  • Reverse osmosis: reverse osmosis expansion tanks are meant to provide clean water storage in the water treatment system
  • Potable: Potable expansion tanks are used for your standard water heater
  • Hydronic: hydronic expansion tanks are used for space heating, floor heating, heated walls, etc

Now that we know what an expansion tank is, let’s dive into how it works for both your tankless and tank-style water heaters.


How Does an Expansion Tank Work?

Well, within an expansion tank, there is a pressurized air bladder that absorbs the additional water by expanding and contracting. As the water becomes hotter, it expands and increases the pressure within the tank and plumbing system. However, instead of allowing the pressure to build, the excess water enters the expansion tank.

In short, an expansion tank only contains overflowing water and does not store water permanently. Also, the expansion tank must be pressurized to match the water pressure in the home.

A diagram showing where an expansion tank can be located on a tank-style water heater.

For example, when you boil a pot of water and you have the lid over it, the water begins to condense on the inside of the lid, forming little droplets of water, right? The same concept happens inside your plumbing system. Inside your pipes, that extra pressure is formed and has to go somewhere, that’s where the expansion tank comes in. The device absorbs that extra pressure created from heating the water in your home or business so that it doesn’t just stay in your plumbing system and start putting a lot of strain on your pipes.


How to Install an Expansion Tank

Because expansion tanks come in a variety of sizes and types, installing one is not a “one-size-fits-all” situation. And due to Los Angeles County code, it is mandatory to have one for your home. So installing one is important, but how do you install an expansion tank?

An expansion tank is generally installed directly above the water heater through what is called a “tee-fitting” installed in the cold water pipe. The tank is usually installed vertically, but it is also possible to install it horizontally if it is necessary due to limited space. 

The plumbing fittings you will need depend on the type of plumbing pipes you have and on how the expansion tank is oriented, so we recommend that you consult with a certified technician first for your specific needs. However, the connections are most commonly made with copper pipes and fittings. 

The expansion tank itself usually has a 1/2-inch or 3/4-inch threaded fitting that is joined into the cold water pipe through a tee fitting and short lengths or threaded or sweat-soldered pipes. We recommend that you consider installing an extra valve before the expansion tank, which will allow you to isolate the tank from the system for easy replacement when necessary. By the way, it is also important to check if your expansion tank works with the water heater you have at home to ensure that the expansion tank can provide enough space for the expanded air.

With all of this in mind, it is usually a good idea to hire a professional to install an expansion tank. While it is possible to install an expansion tank yourself, it’s not a job for inexperienced do-it-yourselfers. This is because there are many risks involved with installing an expansion tank, as it can cause damage to your pipes, your water heater, or your home.


How to Check If an Expansion Tank is Working Properly

Knowing how an expansion tank works is important as it is a key way to know when it’s not working properly. But how can you tell that your expansion tank is not properly functioning?

The easiest way to tell if your expansion tank is working properly is if there's nothing happening with it in general. If there's no leaking or drippage and your home is still supplied with hot water, then everything is in working order. If you're not getting the hot water you need, then there's probably air in your plumbing, signaling a failing expansion tank.

You can check for a damaged expansion tank by looking at a few things: 

  • Condensation

If you see condensation on your expansion tank, you may have an issue. 

  • ‘Knock Knock’

Another way to check if your expansion tank is having an issue is by knocking or tapping on the tank. In theory, the tank should be full of air and give off a hollow sound when tapped upon. If your expansion tank makes a dull sound instead of a hollow one, it means your tank is likely filled with water and will need to be repaired or replaced.

  • Touch

Feeling the tank is another key way to know if your expansion tank is experiencing a problem. The expansion tank should be cool where it's holding air and warm where it's holding water. If over half the tank is warm to the touch, there may be an issue. 

  • Leaks

Visible leaks can signal issues with your expansion tank.


Closing Out Installing Expansion Tanks

Installing an expansion tank is considered an easy task if you know what you are doing. We recommend that you call a certified technician to install your tank to avoid running into any problems with your pipes or water heater and to ensure that your home is up to Los Angeles County code.

Want to learn more about an expansion tank? Read the article below as we help you better understand why tankless water heaters leak (*Hint: it could be your expansion tank or lack of one.) We also shared a link to our basic vs premium tankless installations with Monkey Wrench Plumbing, Heating & Air as we do include an expansion tank in our installation.

Top 3 Reasons Tankless Water Heaters Leak

Basic vs Premium Tankless Installation with Monkey Wrench

When it comes to tankless water heaters and their add-ons, like an expansion tank, Monkey Wrench Plumbing, Heating & Air wants to set you and your home up for success. If you live in the Los Angeles area and would like to have an expansion tank installed on your water heater, click the “Book” button below. Or if you have any other questions regarding expansion tanks you can call us at 310-853-8690, and one of our call center representatives would be happy to help you.