10 Easy Ways On How to Install Expansion Tank On Gas Water Heater

Plumbing Water Supply Check. Caucasian Plumber Worker Testing

Have you ever wondered why most households install an expansion tank for water heaters? Well, water expands when heated. If your water tank has a capacity to hold 50 gallons of water, it can expand to 52 gallons or more when the water is heated?

So, where does the excess water go? Your guess is as good as mine – to your expansion tank.

In the past, excess expanded water makes its way back to the city water supply. However, there is a possibility that the best tankless electric water heater from your home can contaminate the public expanded water supply. Thus, changes were made in plumbing regulations, and Backflow Preventers were required in households.

Without the expansion tank, hot water will have nowhere to go. This situation would significantly increase the pressure in the water pipes, and it can lead to damage in your plumbing, appliances, and in your hot water heater.

It would be very stressful to deal with a damaged plumbing system, so installing an expansion tank would be a great way to spare you from unnecessary stress.

Now, the question is how to install expansion tank on gas water heater?

Well, that’s what this article is for. We will run you through a step by step guide on how to install expansion tank on your gas water heater. Installing an expansion tank can be a do it yourself job – as long as you have the right tools and the correct guide, you will be able to install your expansion tank in no time.

So, first things first. What are the things that you will need for the installation? Good news is, you won’t need a lot of tools for the installation. You just have to prepare these materials:

  • Pipe Wrench
  • Water Heater Expansion Tank
  • Teflon Tape
  • Drilling Machine
  • Screws
  • Tee Fitting or Saddle Valve/ check valves

Now, we’ll walk you through the step by step guide for the installation:

Step 1: Determine the Water Pressure

Three pressure gauge in boiler room, next to heat conductor

It is crucial to determine the water pressure in your home before you start the installation. You have to check and record the hot water pressure within 24 hours using a pressure gauge.

The recommended hot water pressure is from 50 to 60 pressure per square inch (PSI). If your water pressure is more than 80 PSI, then you have to install a Pressure Reducing check valves.

Step 2: Determine the Size of your Thermal Expansion Tank

You can use an online calculator in websites to check the size of your expansion tank. For residential houses, it is common to use 2 to 5 gallons of expansion tanks. If you are unsure, it would be better to install the bigger size. If you install an expansion tank smaller than what is needed, this can lead to relief valve discharge because of excess pressure.

Step 3: Shut Off Water Supply

Plumbing Water Supply Check. Caucasian Plumber Worker TestingTo ensure your safety for the installation, make sure to turn off the water supply. Turn off the hot water from the main supply line.

Step 4: Turn off the Gas

If you are using a gas water heater, turn off the gas supply to your heater. If you don’t know how to turn off your gas supply, then contact your gas company and let them do the job.

This is extremely important because if this is not done correctly, dangerous gasses can build up in your house and a small spark can ignite them, leading to a more significant hazard. These harmful fumes can also bring in illness and death to your family if it gets inside your house.

Step 5: Locate the Cold-Water Supply

Expansion tanks are usually connected to the cold water supply, so you have to identify which of your pipes is the cold water supply.

Step 6: Install Your Expansion Tank

Saddle ValveHang your expansion tank above your cold water supply. Make sure it will be accessible to the horizontal part and the expanded water  heater.

If you are using a Saddle Valve/ check valves, you just have to bolt it in properly, and there will be no need for soldering.

You have to make sure that your expansion tank is securely fastened and is well supported to the wall. Once water expands, it will be carrying the additional weight so it must be able to withhold the extra hot water it will carry. If the expansion tank would fall, it can cause damage to your water heater and the surrounding areas.

Step 7: Connect the Tank

Connect your tee fitting to the pipe of the cold water. Afterward, use your Teflon tape at the end of the connector and use the wrench to tighten the connection. Make sure that you do not over tighten the connection so that it won’t break.

Step 8: Check the Air Pressure of Your Expansion Tank

Using a tire gauge, check the air pressure of your expansion tank. Then, adjust the air pressure. It has to be the same as the maximum hot water pressure in your home. Use the hand pump in adjusting the pressure because if you use an air compressor, it might rupture the air bladder.

Each expansion tank has an air bladder which is pressurized with air. It expands and contracts to absorb the expanded water from your water heater.

Step 9: Remove Trapped Air

Turn on your gas heater and water supply. Then, turn on your hot water faucet until steady flow to remove trapped air from the other side of the bladder.

Step 10: Check if it is Working

There are three ways to check in your expansion tank is working. Assuming that the expansion tank is working well, it’s diaphragm will separate water and air. Air must be on the upper part while water should reside at the bottom.

First, you can tap the upper and lower portion of the tank. If you tap the upper part and it gives a hollow sound, then your expansion tank is working well.

Another way is to check the temperature of your tank. The upper area must be cold because this is where the air is located. The bottom part must be warm because this is where the heated water is stored.

Lastly, you can check the pressure inside the expansion tank using a manometer. The result should be the same as the manufacturer’s specifications. If the pressure inside your water heater is high, then your expansion tank is not working properly, and this can lead to dripping.


There you go! Installing an expansion tank is not as difficult as you think. You can do it yourself, or you can seek the help of the plumber. Either way, it is important to install an expansion tank to your water heater to prevent any plumbing damages.

If you decide to do it yourself, make sure that you follow the step by step guide provided above. You also have to take note of the precautions mentioned to prevent any accidents and for you to install your water heater expansion tank successfully.

Installing an expansion tank is required in some places as regulations mandate them to do so. Check the regulations in your area to make sure that you are compliant with the requirements.

Think of expansion tanks as prevention to a bigger problem – a plumbing disaster. With an expansion tank, the pressure will be regulated, and excess water can be stored.

We hope that we were able to provide you with a comprehensive guide on how to install expansion tank on gas water heater. Let us know in the comments section if you were able to install your expansion tank successfully. We are looking forward to hearing about your success story!






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