What Happens If You Don‘t Use An Expansion Tank? A Complete Guide

Having the proper expansion tank installed on your water heater is critical to avoid serious issues caused by thermal expansion. But what exactly does an expansion tank do and what risks are you exposing your plumbing system to without one?

After seeing far too many problems caused by unchecked thermal expansion from my years as a plumber, I put this guide together to walk you through everything you need to know. I‘ll explain what thermal expansion is, the dangers it poses, when an expansion tank is required, how to size and install one properly, and routine maintenance to keep it working smoothly.

Whether you‘re installing a new water heater or maintaining an existing one, understanding expansion tanks is key to maximizing performance and avoiding costly repairs down the road. Let‘s dive in!

What is Thermal Expansion?

Thermal expansion is the increase in volume and pressure that occurs in water when it is heated. As water temperature rises, its density decreases and molecules spread further apart, taking up more physical space.

For example, water heated from 90°F to 140°F (typical hot water heater temperatures) causes water to expand in volume by 3-5%. In a 40 gallon residential unit, that can mean 1-2 gallons of expanded water in the tank and pipes!

This expansion is determined by the coefficient of thermal expansion – the degree to which a material expands with increasing temperature. For water, this ranges from 0.0001 in/in/°F to 0.0002 in/in/°F.

Without accounting for thermal expansion, the heated water takes up more space but has nowhere to go in a closed-loop plumbing system. This results in a rapid and dangerous pressure buildup unless an expansion tank is there to absorb it.

Dangers of Not Using an Expansion Tank

Based on hundreds of water heater service calls over the years, I‘ve seen firsthand how destructive unchecked thermal expansion can be. Here are some of the most common issues you risk by not having an expansion tank installed:

Water heater damage – Excess pressure can warp and deform the water tank, causing leaks and leading to complete failure. Replacement costs often exceed $1000.

Pipe and valve damage – Pressure spikes from thermal expansion can cause water hammer, which is the loud banging or hammering noise from sudden changes in water direction. Water hammer can damage pipes, valves, and joints, leading to leaks. Fixing water hammer damage averages around $200.

Corrosion and minerals – Pressure fluctuations corrode the water tank walls and pipes from the inside over time. This leads to rusty water, reduced efficiency, and leaks. Rapid pressure changes also allow scale and mineral deposits to accumulate and harden on components.

Higher energy bills – The constant expansion and contraction causes the water heating elements to cycle on and off more frequently as it struggles to regulate temperature. This excessive cycling uses more energy over time, driving up electric bills.

Safety hazards – If pressure climbs too high, the pressure relief valve will leak or burst. This can lead to flooding, scalding from hot water discharge, and deterioration of the valve requiring replacement.

Table 1 summarizes the most common risks and average repair costs associated with thermal expansion in a plumbing system without an expansion tank installed.

When Are Expansion Tanks Necessary?

Any pressurized, closed-loop water heating system needs an expansion tank – I can‘t stress this enough. Here are some of the most common setups that require one:

• Storage tank water heaters
• Tankless/on-demand water heaters
• Boilers used for heat and domestic hot water
• Solar water heating systems
• Radiant heating systems

Many local plumbing codes now require expansion tanks too. For example, the 2018 Uniform Plumbing Code adopted in many states mandates expansion tanks in any system over 199,000 BTU/hour. Some jurisdictions even require retrofitting older systems.

Always check your local plumbing code for specifics on expansion tank requirements in your area. Installing them during new construction or renovations is far easier and cheaper than retrofitting one later.

Signs Your System Needs an Expansion Tank

From spending thousands of hours troubleshooting plumbing issues over the years, I‘ve learned to recognize symptoms of unchecked thermal expansion. Here are some dead giveaways:

Dripping/leaking P&T valve – The pressure and temperature relief valve is dripping or leaking water. This means pressure is getting too high, jeopardizing the valve‘s integrity.

Pounding pipes or water hammer – Loud banging noises from sudden pressure changes as water is used. This can damage pipes and valves over time.

Rusty/discolored water – Corrosion inside the tank or pipes mixes iron into the water, giving it a rusty tint.

High energy bills – Frequent cycling on and off from pressure fluctuations causes excess energy usage.

Creaking water heater – Buildup of pressure can warp the internal tank, causing creaking or popping sounds as it expands and contracts.

If you notice any of these warning signs, I‘d recommend having an expansion tank installed or thoroughly inspected if one is already present. The fix is far cheaper than repairing the impending damage down the road!

How to Install an Expansion Tank

Adding an expansion tank to an existing water heating system is actually a pretty straightforward DIY project. Here is a step-by-step overview:

1. Turn off water supply and power

Shutting off the water supply and power to the water heater provides a safe work environment. Be sure all hot water taps are turned on to relieve pressure too.

2. Select location

Pick an accessible location along the cold water inlet line going into the water heater. Install it as close to the tank as possible, but always after the main shut-off valve and backflow preventer if present.

3. Mount tank

Use the provided straps or brackets to securely mount the expansion tank to a wall or stud. It should be supported but still allow access to service.

4. Connect to plumbing

Using the proper fittings for your pipe size, connect the expansion tank to the cold water inlet line leading to the water heater.

5. Charge tank

Use a bicycle pump or air compressor to charge the expansion tank‘s air bladder to 2-3 PSI less than the working pressure of your plumbing system. This gives thermal expansion room before reaching maximum pressure.

6. Turn water back on

Slowly turn the main shut-off valve to refill the system. Check for leaks during pressurization. Confirm proper expansion tank pressure.

7. Flush tank

Once pressurized, open the nearest hot water faucet and let it run until hot to flush the tank and lines of any debris that may have entered during service.

And that‘s the basic process for installing an expansion tank! Now let‘s go over proper sizing and placement.

Proper Sizing and Placement

Choosing an expansion tank that‘s too small won‘t properly handle thermal expansion. Follow the manufacturer‘s sizing guidelines based on your water heater‘s capacity.

As a general rule of thumb:

• Residential systems up to 120 gallons need a tank equal to 10% of total system volume

• Large residential and commercial systems over 120 gallons need a tank equal to 4-5% of total volume

For example, a 40 gallon residential unit would need a 4-5 gallon expansion tank minimum.

In terms of placement, the key is installing the expansion tank immediately on the cold inlet line, after any main shut-off valve or backflow preventer. This allows the tank to absorb thermal expansion before excessive pressure reaches the hot water system.

Here are the recommended expansion tank locations from major manufacturers:

Pay close attention to properly sized connectors and supports, and always follow local code requirements too. Taking the time to correctly size and position the expansion tank will ensure it adequately protects your plumbing system.

Routine Maintenance Is Crucial

While expansion tanks are built to last, I recommend inspecting and servicing them at least once a year to maximize their lifespan:

• Check air pressure – Use an accurate pressure gauge to verify the expansion tank is charged to 2-3 PSI under your plumbing system pressure. Top it off as needed.

• Inspect for corrosion – Check the external shell and connecting pipes for corrosion and rust. These can indicate a failing tank.

• Clean debris from valves – Use a rag to wipe away any debris around valves and fittings. Mineral deposits can cause them to malfunction over time.

• Listen for water sloshing – If you hear water moving inside the tank, it means the bladder is damaged and can no longer separate air and water. Replace tank immediately.

• Watch for leaks – If you see any water leaking, replace faulty valves or fittings. Leaking tanks must be replaced.

With periodic maintenance, your expansion tank should last 8-12 years depending on water quality and usage. Catching small issues now protects you from huge headaches down the road!

Helpful Expansion Tank Tips

Here are some additional pointers from hundreds of plumbing calls to help your expansion tank installation and maintenance go smoothly:

• Record tank size and pressure settings on the tank or nearby with permanent marker for easy reference.

• Shut off the water and relieve pressure before servicing. Tanks hold high pressure – safety first!

• Install an isolation valve before the tank for easier maintenance. Shut it off and drain the tank completely to service.

• Don‘t undersize the expansion tank line diameter. This creates backpressure and renders it ineffective.

• Avoid installing below the overflow level of the water heater to prevent backflow of hot water.

• If your tank runs out of air pressure quickly, you likely have a larger issue allowing water in.

• For difficult access locations, install a remote expansion tank kit which allows recharging the air from a distance.

And if you have any difficulty installing or maintaining your expansion tank, don‘t hesitate to call in a professional. It‘s a small investment to ensure this critical system is functioning properly for years to come.

Conclusion

I hope this guide provided you with a complete overview of thermal expansion tanks and just how important they are for avoiding catastrophic damage and safety hazards.

While the basics of sizing, installation, and maintenance are straightforward, there‘s no substitute for years of experience recognizing issues before they become major problems. Don‘t hesitate to tap into professional expertise when needed.

A properly functioning expansion tank is one of the most important accessories for maximizing water heater performance and longevity. Take the time to understand how they work and ensure yours is protecting your system. It‘s one plumbing issue you certainly don‘t want exploding out of control!

Stay safe out there,

Lillie Gabler, The Plumbing Doctor