Can You Install An Expansion Tank Upside Down?

Knowing an expansion tank’s structure and working is crucial to understanding where and how it is installed and if it should be connected to the cold or hotline.

Expansion tanks are heating system safety devices that protect pipes and fixtures that are part of the plumbing system. Especially ones that have a missing check valve or backflow prevention system.

The local plumbing laws in most areas require the installation of expansion tanks whenever a new water system is placed on the municipal’s main water supply. Generally, expansion tanks are installed right above the water heater on the cold water line in an upright orientation. They may also be installed upside down or horizontally, which requires added support to keep them in position.

Expansion tanks are filled with air which allows room for greater water volume when it is heated. Today, we shall look at the most common questions about expansion tanks and the correct method of DIY installation.

Let’s get straight to it!

Can Expansion Tanks Be Installed Upside Down?

Ideally, an expansion tank is often installed upright but can be installed in any direction. The tank will function properly even if it is placed upside down or horizontally, given that there is enough strapping support to secure it in place. Improper support can lead to break-off from the mounting pipe if the tank fails and gets filled with water.

Where Are Expansion Tanks Installed?

Generally, an expansion tank is installed on top of the water heater horizontally on the cold water line. If limited space is available, the tank can also be installed vertically. The type of fittings required to complete installation depends on the fittings, pipe type, and tank orientation.

Pipes are connected using copper fittings. A tee-fitting connects the expansion tank’s ¾ inch fitting to the cold water line. This connection is made using short pipes, sweat-soldering, or threading.

Tools Required During Installation

  • Soldering tools
  • Channel-lock pliers/pipe wrench
  • Copper tee-fitting (0.75 inches)
  • Pipe-sealing tape
  • Dielectric water heater nipple
  • Extra copper fitting (0.75 inches)
  • Thermal expansion tank
  • Copper pipe (0.75 inches) and copper flex pipes
  • Two female-threaded copper unions (0.75 inches)

Prepping Up For Expansion Tank Installation

It is necessary to drain the water from your heater if you already have an expansion tank installed. Also, ensure there is sufficient space above your water heater before beginning installation. New installations do not require draining, and you can directly start installing your tank. If drainage is required, then you should follow the steps below:

  1. Cut off the main water supply line that supplies water to the cold pipeline.
  2. Connect a hose to the heater’s drain valve to redirect it to the closest drain.
  3. Relieve pressure from the heater by opening the drain towards the closest faucet’s hot side and the water heater itself. Make sure to open up the valve slowly to prevent a slide.
  4. Keep draining for a few minutes, then open up your T&P valve to check the pressure. If all the pressure has been released, you can continue with the next step. Else, you can wait for some more time.
  5. Close the faucet and your drain valve.

Expansion Tank Installation Guide

The first thing you need to do is to plan your installation. Make sure to measure and confirm that you have sufficient space for installing your expansion tank above the heater. Also, check whether the tank will fit upright or if you must make do with other tank positions. 

Once you have everything planned and are ready with all the necessary tools, begin by positioning your tank in place. Next, follow the steps below to install your expansion tank correctly:

  1. Connect a dielectric union to the cold water entry valve. Use pipe-sealing tape to wrap the threads of the union. Next, thread it into the cold water port inlet on your water heater. Use a channel-lock plier or a pipe wrench to do this.
  2. Use pipe sealing tape and wrap it around the top-most threads of the union. Next, the female threaded copper adapter must be passed onto the union.
  3. Use a channel-lock plier or pipe wrench to tighten the copper adapter and secure it.
  4. Place a tee-fitting and short copper pipe on the dielectric union of your water heater. Keep the fitting at least 1 foot above the heater to allow enough clearance for the expansion tank. You can use sweat soldering or push-fit/shark-bite to secure the connections.
  5. Place a short horizontal copper pipe into the tee-fitting’s side outlet. The length of the pipe should be based on the available space (6 inches or less). Connect a female threaded adapter and make a secure connection using the method of choice.
  6. Place the pipe-sealing tape on the threaded fitting of your tank and screw the adapter to the horizontal pipe. Do not overtighten, as this can damage fittings.
  7. Finally, connect the cold water line to the top of your tee-fitting using the necessary pipes. It is a good idea to use a copper flex line. Finish off with hot water connections and turn on your heater and valves for a test operation. Check for leaks, and if all is clear, you are good to go.

How Do Expansion Tanks Function?

Expansion tanks allow a water heating system to last long and are necessary in certain conditions. Water tends to expand when heated; an expansion tank is crucial for containing this expansion to prevent major damage to a plumbing system.

The volume of water rises by about 2% when heated from 50 degrees Fahrenheit to 120 degrees Fahrenheit. Extra space to allow room for this expansion will prevent extra pressure/load on the water tank, fixtures, and pipes. This ultimately reduces the chance of water bursts.

An expansion tank is a necessary installation in a closed plumbing system. It prevents water from putting excess pressure on backflow valves/pressure-limiting valves and reverting back to the main water supply. The expansion tank comprises two parts:

  • An air chamber that builds pressure on diaphragm expansion.
  • A water section that accommodates water when expansion occurs upon heating.

Is The Installation Of Expansion Tanks Mandatory?

In most areas, it is necessary to have a plumbing license or permit if you wish to install a water heater. They will guide you about other requirements while getting the permit and will often tell you it is mandatory to get a water expansion tank installed as well.

If pressure-limiting or backflow valves are in position, it may not be necessary to get one, but the need to abide by local rules may make it necessary.



An expansion tank may not be necessary if you have pipes with fittings that can prevent backflow, but they are a definite requirement in most areas. It is a good idea to know how you can install one yourself using the steps we have explained above. 

While most people prefer installing it in an upright position, there is no harm in changing the orientation of your tank to fit it in your desired space.

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