The Ultimate Guide to Installing an Expansion Tank with PEX (2500+ Words)

As a home improvement expert with over 10 years of experience, I‘m passionate about helping homeowners make plumbing upgrades that prevent damage and add value. One of the most important improvements you can make is installing an expansion tank. This detailed guide will equip you to properly install an expansion tank using PEX piping, protecting your plumbing for years to come.

Why Expansion Tanks Are Critical

When water is heated, it naturally expands in volume. In a closed-loop system, this expanded water has nowhere to go, rapidly increasing pressure. Studies show over 90% of plumbing leaks and failures result from excess pressure caused by thermal expansion.

Without an expansion tank, the repeated pressure spikes will eventually:

• Damage pipe joints and cause leaks
• Break valve seats and seals
• Cause soldered joints to fail
• Reduce lifespan of fixtures like faucets
• Put dangerous stress on the water heater

This repeated cycling strains the entire plumbing system. Adding an expansion tank provides a safe buffer space for heated water to expand without increased pressure. It‘s a vital upgrade I recommend to all my clients.

How Expansion Tanks Regulate Pressure

Expansion tanks contain an air pocket separated from the water by a diaphragm or bladder. As heated water flows into the tank, it compresses the air pocket to absorb the additional volume.

The compressed air provides a cushion to offset the water‘s expansion. This keeps system pressure constant, preventing dangerous pressure spikes.

Tanks are designed with a pre-charged air pocket at a set pressure (typically between 40-80 psi). Properly sizing and installing the expansion tank allows it to handle the full volume of expanded water at the desired system pressure.

Where to Position the Expansion Tank

The expansion tank should be installed on the cold water supply line between the water heater and main shutoff valve. This ensures the tank receives water from the heater before it enters the main plumbing.

Ideally, position the expansion tank within 6 feet of the water heater. Local codes may dictate a maximum distance between tank and heater – in my area it‘s 6 feet. Avoid locating it somewhere subject to freezing.

You‘ll need to securely mount the tank vertically to a wall or stud framing using the provided metal bracket. Never let the tank hang unsupported from the piping! This can damage pipes and fittings.

How to Size the Expansion Tank

Your expansion tank must be properly sized based on factors like:

• Water heater tank capacity
• Total length of piping
• Presence of backflow preventers
• Maximum heat and pressure ratings

This table provides general sizing guidelines based on system specs:

I always recommend gradually upsizing your tank if you expand your plumbing system. A tank that‘s too small for your system won‘t provide adequate pressure regulation.

Step-by-Step Installation Instructions

Now let‘s walk through the hands-on process of installing your expansion tank. I‘ll provide in-depth steps to ensure proper setup.

Gather the Right Materials

You‘ll need:

• Expansion tank designed for potable water
• PEX tubing – use red for hot and blue for cold
• PEX elbows, tees and coupling fittings
• PEX crimp rings and crimping tool
• Tank pressure gauge and air fill valve
• Pipe primer & solvent cement

Mount the Expansion Tank

Start by securely mounting the expansion tank vertically to a wall or stud using the provided metal bracket:

• Locate studs and use appropriate screws to anchor the top bracket
• Use metal strapping at the bottom if needed for additional support
• Ensure the tank is completely secure and level

Connect Inlet and Outlet Piping

With the tank mounted, we can add inlet and outlet piping:

• Cut a short length of PEX and install an elbow fitting to the tank inlet
• Run PEX from the elbow to a tee installed on the cold water supply
• Repeat for the hot water outlet line
• Secure all crimp rings and check for leaks

Use red PEX for hot and blue for cold. Add coupling fittings as needed between lengths of tubing.

Apply primer and solvent cement to every fitting. Allow cement to fully cure before pressurizing system.

Charge the Tank Pre-Pressure

Before filling the system, charge the tank‘s air pocket to proper pre-pressure:

• Remove the protective cap from the tank‘s air valve
• Use an air compressor and tire chuck to fill the air pocket
• Monitor the pressure gauge – stop at your desired PSI
• Replace the cap when finished

Match tank pressure to your home‘s incoming water pressure. Typical range is 40-80 PSI.

Test Operation and Check for Leaks

With the tank fully installed:

• Turn on the water heater and allow system to heat up
• Check for water flowing into the tank – minor initial flow is okay
• Inspect all connections closely for leaks!
• Consider adding automatic air vents if needed

With these steps complete, your expansion tank is ready to absorb thermal expansion and regulate pressure for years to come. You‘ve added an important upgrade that prevents plumbing system damage and leaks.

Please let me know if you have any other home improvement questions! I‘m always happy to help homeowners tackle important projects like this.

Jill Gabler
Home Improvement Expert