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Does My Water Heater Need an Expansion Tank?

August 31, 2017

The short answer? Most likely. In fact, the city of Boulder states that if you have a “closed” plumbing system, you are required by law to have an expansion tank installed.

Some manufacturers may even void your water heater warranty if you have a closed plumbing system but don’t have an expansion tank for your water heater.

You see, expansion tanks work like shock absorbers on your car. They absorb excess water pressure, protecting your water heater from damage and early failure. 

Not sure what a closed plumbing system is or how to determine if you have one? We’ll explain.

Already know you need an expansion tank? Just contact us for a quote and reliable installation.

What’s a “closed” plumbing system?

Homes have either “closed” or “open” plumbing systems. In a “closed” plumbing system, water can’t flow back into the city water lines once it enters your home’s plumbing. 

Now that might not seem so bad but if you don’t have an expansion tank, a closed system doesn’t give expanded water any route for escape, causing damage to your home’s water heater and plumbing.

Here’s what we mean: When water is heated inside your water heater, it expands. This is called “thermal expansion”. For example, the cold water in a standard 50-gallon water heater expands to 52 gallons when heated to 120°F. That extra water volumeraises the pressure in your water heater to dangerous levels.

So how does that extra pressure affect your water heater? Well, think of thermal expansion in your water heater as bending a paperclip back and forth. Eventually, the paperclips breaks, right?

The same thing happens to your water heater. Your water heater tank isn’t designed to expand and contract to accommodate for thermal expansion and will eventually burst.

That’s where an expansion tank comes into play.

As water heats inside the water heater and exceeds the capacity of the tank, the overflow rushes into the expansion tank.

When an expansion tank is installed, the extra water volume automatically rushes into the tank. This lowers the water pressure inside your water heater to safe levels, protecting your tank (and other water appliances) from damage.

How do I know if I have a “closed” plumbing system?

Bottom line: If your home has any kind of backflow prevention device installed on your home’s main water line, your home has a closed plumbing system.

These “backflow prevention” devices stop the water from flowing out of your home’s plumbing and back into the municipal water lines.

Where to look:

Backflow prevention devices are always connected to your main water shutoff valve. In Colorado, main water shutoffs are usually located:

  • In a basement
  • In a utility room/closet
  • In a crawl space

Note: It’s very rare for the main water shut off valve to be located outdoors in Colorado homes.

You may have difficulty pinpointing the backflow prevention device on the main water line because these devices vary in appearance. However, most should look similar to this backflow prevention device

If you can’t determine whether you have one, have a professional plumber perform this task.

Note: Don’t have a backflow prevention device? Then you have an “open” plumbing system, which allows water to flow back into the city’s water lines as it expands, preventing high water pressure situations. While expansion tanks aren’t required for open water systems, you could still benefit from one. Ask a plumber if you should still consider installing an expansion tank.

Need an expansion tank installed? Ask a Denver plumber

If you need an expansion tank installed, just contact us. We’ll send over one of our trusted plumbers to inspect your system and give you a fair quote for the job.

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