Overview

When you install a water heater, there's more to think about than just hot showers. As water heats up and expands, all that extra pressure can strain your plumbing system. That’s why many setups include an expansion tank to give that pressure a safe place to go.

In this post, Knights Plumbing, LLC. explains why expansion tanks matter, when you need one, and how they help protect your water heater and pipes from damage.

Highlights

Introduction

When installing a water heater, it’s easy to focus on the big equipment and forget about the smaller parts that make the whole system work safely. One of those parts is the expansion tank. If your home has high water pressure or a closed plumbing system, skipping this step can lead to leaks, pressure issues, or even water heater failure.

In this blog, we’ll walk you through the importance of installing an expansion tank alongside your new water heater.

What Is an Expansion Tank?

An expansion tank is a small add-on that connects to your water heater and helps manage pressure in your plumbing system. Inside, it has a rubber bladder that separates the tank into two sides—one holds air, and the other absorbs extra water when things heat up.

You can think of it like a shock absorber for your pipes. As water heats and expands, it needs somewhere to go to relieve pressure. In a closed plumbing system, there’s nowhere for that extra pressure to escape. Without an expansion tank, all that buildup pushes against your pipes, fittings, and water heater, which can lead to damage over time.

How Thermal Expansion Affects Your Plumbing

As water heats from room temperature to around 120°F, it expands by roughly 2% in volume. In an open plumbing system, this extra water can flow back into the municipal supply without causing problems. However, in a closed system, like one with a backflow prevention valve or a pressure-reducing valve, there’s nowhere for that added volume to go.

Without a buffer in place, you may run into issues like:

  • Rising water pressure: Excess pressure builds up throughout the plumbing system.
  • Added strain on pipes, fixtures, and the water heater: This strain accelerates wear and the risk of breakdowns.
  • Leaks, cracked tanks, or failed joints and valves: These are common results of unchecked pressure buildup.

An expansion tank helps prevent these problems by giving the extra water a place to go when it heats up. Instead of building pressure in your pipes, the tank absorbs it and helps keep everything working the way it should.

Why You Might Need an Expansion Tank on Your Water Heater

If you’ve never heard of an expansion tank before, you’re not alone. But if your water heater has been acting up or you’re upgrading your plumbing system, it’s something worth knowing about.

Here’s how to tell if your home could benefit from one:

1. You Have a Closed Plumbing System

Some homes have what’s called a “closed” plumbing system. That just means there’s a valve in place (like a check valve or pressure-reducing valve) that keeps water from flowing back into the public water supply. While this helps with safety, it also means pressure has nowhere to go when water heats up. That pressure can build dangerously, but an expansion tank gives it a safe place to go.

2. You Just Got a New Water Heater

Today’s water heaters are more efficient and high-tech than ever. But with that comes sensitivity to pressure changes. Some newer models can shut off completely if the pressure goes too high, so an expansion tank can help keep things running smoothly.

3. Your Local Plumbing Code Says So

In many areas, having an expansion tank isn’t optional. If you have a closed system, local codes often require one. It’s also something home inspectors check for, and skipping it could affect your warranty or cause problems during a future home sale.

4. You’re Seeing Plumbing Problems

Sometimes, your house gives you hints.

Watch for signs like:

  • Water leaking from the temperature and pressure relief valve
  • Water pressure rising and falling while using a tap
  • Unusual sounds coming from the water heater
  • Leaking around fittings or valves

This could mean pressure is building up too much in your system. An expansion tank can relieve that pressure and keep minor problems from escalating.

Benefits of Installing a Proper Expansion Tank

Beyond avoiding code violations or plumbing headaches, a properly installed expansion tank can significantly improve the performance of your system.

An expansion tank:

Extends the Life of Your Water Heater

Too much pressure wears down the inside of your water heater faster than you’d think. An expansion tank eases that pressure, helping the unit last longer and work more efficiently.

Prevents Damage to Plumbing Fixtures

Thermal expansion can send tiny pressure waves through your pipes that impact everything from your faucet seals to your dishwasher. By smoothing those spikes, an expansion tank helps protect parts you might not even realize are under stress.

Helps Maintain Consistent Water Pressure

If your water pressure randomly jumps or drops, especially when using multiple taps at once, thermal expansion might be the reason. An expansion tank helps keep pressure more stable, making showers and laundry cycles more predictable.

Reduces Risk of Water Damage

When pressure gets too high, leaks can pop up in unexpected places, leading to stains, warped floors, and costly repairs. Adding an expansion tank is a small upgrade that can prevent big messes down the line.

The Hidden Costs of Skipping an Expansion Tank

Replacing a water heater isn’t just about swapping the old one for a new model. It’s also a chance to make sure your entire hot water system is set up for long-term performance, including managing pressure the right way.

While an expansion tank isn’t strictly necessary, opting out of installing one can quietly lead to expensive problems. Without one, thermal expansion puts stress on your pipes, valves, and appliances every time your water heater kicks in.

As the system ages, that added pressure can lead to:

  • Leaking joints: Wear down faster than expected
  • Failing valves: No longer hold pressure reliably
  • Cracked pipes or fittings: Often hidden behind walls and expensive to fix
  • Inconsistent hot water: An inconvenience caused by pressure imbalances in the system

The Damage Doesn’t Show Up Right Away

These problems don’t always appear right after installation. In many cases, signs of stress, which include leaks, pressure issues, or hidden damage, can take months or even years to show up. By the time they do, warranties may have expired, and repairs can be more complex and expensive.

Taking steps to manage pressure from the start, like adding an expansion tank, helps prevent these long-term surprises and preserves your new water heater for a lot longer.

New Water Heaters Are More Vulnerable to Pressure

Today’s water heaters are built to meet modern efficiency standards, which means they heat water faster and waste less energy. That’s great news for your utility bills. However, it also means the water in your system expands more quickly, creating sudden spikes in pressure. Unlike older tanks that could handle a bit more fluctuation, many newer models have thinner walls, smaller footprints, and digital components that are more sensitive to stress.

This shift in design makes expansion tanks more important than ever. When you’re upgrading to a high-efficiency unit or switching to a larger-capacity system like a heat pump water heater, adding an expansion tank helps manage the added pressure from rapid heating. It’s a small addition that supports the performance of your new water heater and keeps your plumbing system running smoothly.

Repairs Can Cost You Much More Later

When installing a new water heater, it’s tempting to stick with the basics and skip any extras. However, some additions aren’t really “extras”—they’re smart long-term decisions. An expansion tank is one of those things that quietly does its job in the background, offering added protection without requiring any ongoing attention.

It’s not a matter of simply spending more—it’s a matter of avoiding unnecessary problems later. Once it’s in place, an expansion tank helps your system run better, protects everything it connects to, and gives you the confidence that your upgrade was done right from the start. For such a simple component, the peace of mind it brings is hard to beat.

Maximize Your System with Our Water Heater Installation Service

When you’re investing in a new water heater, don’t settle for the minimum. Give your system the support it needs to last longer, perform better, and run safely. An expansion tank is a high-demand plumbing accessory and a smart layer of protection for your home.

If you’re unsure whether your home needs one or want a quote for a bundled installation, Knights Plumbing, LLC. is here to help. We install water heaters complete with everything needed to match your home’s water pressure, system type, and heater size. Give us a call at (763) 286-9941. We’re happy to walk you through your options.