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Everything You Need to Know about Thermal Expansion

As a homeowner, chances are you’ve never really thought about thermal expansion
and how it relates to your home. But thermal expansion is a big deal for a homeowner,
and it can cause real damage to your home if you’re not prepared


As a homeowner, chances are you’ve never really thought about thermal expansion and how it relates to your home. But thermal expansion is a big deal for a homeowner, and it can cause real damage to your home if you’re not prepared.

What Does Thermal Expansion Mean, and Why Does It Matter?

Merriam-Webster defines thermal expansion as the “increase in linear dimensions of a solid or in volume of a fluid because of rise of temperature.” To better visualize how this works in the real world, we need a real-world example.

Have you ever taken a hot drinking glass right out of the dishwasher, poured an ice-cold beverage into it and witnessed the glass suddenly crack? That’s thermal expansion at work. While the glass was going through the wash cycle, it increased in temperature, causing it to expand. When the cold liquid was added to the glass, the inside immediately started to contract. But since glass is such a bad thermal conductor and can’t evenly distribute temperature changes quickly enough, it literally cracks under the pressure.

So how does thermal expansion affect your home? Thermal expansion can affect multiple areas in your home from your windows and doors to your foundation and walls. But the biggest area affected by thermal expansion is your plumbing system.

Thermal Expansion and Your Plumbing System

If there’s one area in your home that’s hardest hit by thermal expansion, it’s definitely your plumbing system. Since all the pipes in your home are full of water at any given time, thermal expansion creates pressure and stress that can cause damage or wear and tear. It all starts with your water heater.

When water enters your home through the water main, some of it is directed into your water heater tank. As that cool water is heated up, it expands. If you have a 50-gallon water tank, you could end up with an extra couple gallons of water after heating. What happens next depends on whether you have an open or closed plumbing system.

Open vs. Closed Plumbing Systems

In an open system, water is allowed to flow both in and out of your home from the water main leading to your city’s municipal water supply. That means that when the water in the water heater tank starts to expand, the excess water flows back through the water main and into the city’s main water supply.

In an ideal world, we’d all have open plumbing systems, and we wouldn’t have to worry about thermal expansion. But there are a couple reasons why these open systems don’t really work.

The first reason is simply that open plumbing systems can become a public safety issue. Contaminants in pipes can be picked up by the water and put into the city’s water supply, putting multiple homes at risk. Most cities have ordinances that require a check valve in every home that prevents water from going back into the supply.

The other factor preventing open systems is pressure. Many municipal water suppliers pump their water out at extremely high pressures, sometimes as high as 150 pounds per square inch (psi). Homes aren’t designed to handle pressure that high, so homeowners and contractors have pressure reducing valves installed to drop incoming water pressure down to a more reasonable level, like 60 psi. Pressure reducing valves only allow water to flow one way, which brings us to the much more common closed plumbing systems.

In a closed system, water can only flow in to your home. So, when your water tank starts to heat up and the volume of the water increases, that extra water has to have somewhere to go. This is usually taken care of by a thermal expansion tank or a pressure release valve, both of which are installed on or near your hot water tank.

The Role of the Pressure Release Valve

The pressure release valve is a basic line of defense for dealing with thermal expansion. It works by allowing a little bit of water to drip out when thermal expansion is happening. Pressure release valves usually have a hose that redirects excess water to a floor drain or water bucket. The Role of the Thermal Expansion Tank

Expansion tanks look like smaller versions of your water heaters. They’re a little tank that gets installed on top of, or adjacent to your water heater. Inside the expansion tank is a little bladder that takes on excess water when your home’s water starts heating up. Expansion tanks keep your water pressure at a consistent level and help prevent damage to your plumbing components.

Thermal Expansion and High Water Pressure

What happens to your plumbing system if you don’t have an expansion tank or pressure release valve? As the water in your pipes heats up and expands, the water pressure in your entire home starts to rise. Since the spike in pressure happens after the water passes through your pressure reducing valve, the pressure gauge will read as if nothing has changed.

But if you pay attention, you’ll notice some of the tell-tale signs of high water pressure:

  • Water hammer. Do you ever hear loud banging sounds coming from your pipes whenever you open or close a faucet? It’s called water hammer, and it’s a red flag that you almost certainly have a pressure problem.

  • Toilet trouble. Water under high pressure has a knack for escaping your pipes, and one of the points of least resistance is your toilet. While a running toilet might be caused by worn out components in your toilet’s tank, it could also be a sign of high pressure.

  • Dripping fixtures. The gaskets in your faucets and showerheads are only built to handle pressures of up to around 80 psi. Anything over that and you’ll notice some dripping even when they’re turned all the way off.

  • Water spots on walls and ceilings. High water pressure can lead to tiny leaks around pipe joints. These leaks can happen in several places throughout your home, usually behind walls and ceilings. If you notice any discoloration on your walls, you might have a small leak that is seeping into the drywall.

Those are just the early warning signs. If you’ve got a water heater that keeps running and doesn’t have a working expansion tank or pressure release valve, you could end up with huge leaks, floods and even a tank explosion as your plumbing system wears out over time.

Keeping Tabs on Pressure

Even if you have a pressure relief valve or expansion tank installed on your water heater, there’s always the chance they could stop working. Here are a couple reasons your expansion tank might fail:

  • Mineral deposits. If your area’s water has a high mineral content, the valve in your expansion tank might be blocked.

  • Bad bladder. Your expansion tank has a rubber bladder inside to keep the air in the tank from mixing with the water it lets in. Those bladders can fail after some time, leading to your expansion tank getting waterlogged.

Since the gauge on your pressure reducing valve won’t register pressure spikes caused by your water heater, you need to find another way to keep tabs on it. You can use a simple pressure gauge to check your home’s actual pressure, but what if you’re not at home and your expansion tank fails? Now there’s a way to accurately monitor your home’s water pressure remotely.

The Flo Smart Water Monitor and Shutoff is a smart water security system that constantly monitors your home’s plumbing. It provides an accurate reading of your home’s water pressure in real-time, 24 hours a day. And it’s smart, which means you can access it from your phone no matter where you are.

Even leaks as small as one drop per minute (which adds up to thousands of gallons of water leaked in a year) are detected by the Shutoff, giving you an early warning system you can use to address problems before they do any serious damage.


You don’t really need to know all the science behind thermal expansion to know how it can harm your plumbing. To keep everything flowing smoothly and protect your home from high water pressure, make sure your thermal expansion tank or pressure release valves are in working order. Finally, monitor your home’s water pressure to prevent future problems.



For more information contact:
Email Address:

Samantha Eastman or Emily Baker

Falls & Co.

Phone: 1-216-696-0229

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