Thermal Expansion | Water Heaters | San Diego

Thermal Expansion and Why It Matters to You!


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At Bill Howe, our plumbers in San Diego stay on top of the ever changing Uniform Plumbing Code (UPC).  Because new technology and new regulations are always begin implemented, it is important that we help to educate our customers.

One of the most frequent changes that our plumbers have seen in San Diego in the last few years surround water heaters, both installation code and the type of water heaters available. We recently talked about new regulations in effect in San Diego county that have increased the cost of water heaters due to the Lo NOx burners. Lo NOx deals with the actual water heater, but there is also a new requirement that affects the installation of all water heaters in San Diego: Thermal Expansion.

What is Thermal Expansion?

Thermal Expansion

The basic definition for thermal expansion is, when water is heated, it expands.

But what does that have to do with your water heater installation?

Thermal expansion affects water heaters because it increases the pressure when they are doing their job-heating water for use in your home or building. For example, when the temperature changes from 90 degrees to 130 degrees, the amount of water will increase by a half gallon. While this change is happening, the pressure and volume of water increases in your conventional tank and has to go somewhere.

Where Does the Excess Go?

In the past, most systems (water) were considered “open.” This means that water from the house flows into the city water supply, and vice versa; it flowed freely in both directions. So, if your homes water pressure rose, it would release that pressure by flowing to the city supply.
Now, the city is protecting their municipal water supply from possible contamination by requiring backflow devices (which you may remember from our previous blog about backflow testing requirements) or protecting it from a home’s pressure fluctuations by closing the system.

The new UPC 608.2 requires a home with a pressure regulator, or any backflow device that prevents dissipation of excess pressure into the main supply to have a thermal expansion tank to control thermal expansion.

What is a Thermal Expansion Tank?

A thermal expansion tank is installed on the water heater and allows a place for the excess water to go when the pressure becomes too high. It protects both the home from increased pressure flowing to other fixtures (often causing leaks) and it protects the flow from going into the city water supply to prevent backflow and possible contamination.

How Do I Know if I Need a Thermal Expansion Tank?

If you have a backflow device, or pressure regulator installed, you must have a thermal expansion tank installed per UPC. In fact, licensed plumbers in San Diego will not install a water heater without this as it would not be to code.

How Many Homes Have Thermal Expansion?

Every home that has a water heater(s) in San Diego will have thermal expansion. Thermal expansion will occur every time the water heater is heating water from turning on a tap, shower, washing machine, etc.

And, it is estimated that only 5 percent of homes in San Diego have a thermal expansion tank.

Does Thermal Expansion Cause Leaks?

Yes! Thermal expansion can be connected to leaks in faucets, toilets, as well as leaks underneath the slab foundation. Excessive pressure strains plumbing fixtures, and especially seals such as you can find in toilets. It also causes water pipes to expand and over time can result in leaks.

If you’re thinking of installing a new tank water heater, you will want to be prepared to talk about a thermal expansion tank. If you want an evaluation on your current system, call one of our experts for a free estimate. After all, our plumbers have been installing water heaters in San Diego for over 35 years and have the knowledge of plumbing code and offer only the best products available to care for your home and family.

Call 1-800-Bill Howe (245-5469) today for the name you trust!

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