Thermal Expansion Tank, IPC 308.10

IPC 308.10 states, “… Thermal expansion tanks shall not be supported by the piping that connects to such tank.”

So, this means the installation in picture is not properly done?

They are almost never supported, in fact I did not even know it was a requirement till now, but looking into it you are right, it should be strapped.

Water weighs about 8 lbs a gallon, meaning that if it ever fills all the way (for example if the bladder ruptures, or it’s under inflated) your expecting that pipe to hold 16-24 pounds.

I will start calling it out now.

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Agree Yossi. It would be especially important in situations where tank is laying over @ 180 degrees, although vertical position is best for operation of bladder. All that I have seen are not supported other than with the piping. Anyone out there seen a tank installation with a legitimate support method and a picture they can post?

I called this out on every new home inspection however when they’re piped with metal piping material the local authority having jurisdiction allows it.

This code was a result of the popularity of PEX piping and using that piping material to support the expansion tank.


This YouTube guide on how to replace an expansion tank show the installation of straps. But even he says that if it’s mounted sideways you have to get creative.

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Logistically how would that even work, it would more be dangling than supporting. Also, it’s kind of redundant because you cannot have Pex with in 18 inches of the water heater, and the expansion tank is almost always right next to the water heater.

I look to see if the weight is supported by any means other than the water piping. If I see this has been accomplished no matter how creative, I am satisfied. I’m not sure about seismic areas.


I’m not sure where you’re hearing this but I can tell you that in the IPC you absolutely can.


You got it Brian this is what I use.


If the tank is mounted vertically as shown in the pic, and supported by metal pipe, I usually just make a statement about additional support based on blah, blah and more blah, or if it’s required by local blah. JMO, it’s not going anywhere the way it’s mounted.

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Welcome to our forum, George!..enjoy participating. :smiley:

604.11.2 Water Heater Connections. PEX tubing shall not be installed within the first eighteen (18) inches of piping connected to a water heater.

But I do see other sources online saying that you could attach it to an electric water heater, so if someone can clarify when this code applies that would be great.

Where is this from? UPC? Always quote source. The UPC covers about what maybe 20% of the United States?

Yes, the UPC is where I got that. The plumbing code for los Angeles, witch is where I am.

I’m not saying you should follow the UPC if it’s not code where you are, but you asked me where I got it from as if I pulled it out of a hat.

Well, you started the thread with ICP, then switched mid thread to UPC and @mwilles caught it.

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The INTENT of the code is to prevent damage to the PEX caused by heat from an exhaust flue pipe, which an electric WH has none.


I asked for the source because of this statement…

I’ve been a licensed plumbing contractor in UPC and IPC both codes vary more than most home inspectors assume. What may not be accepted in your region is accepted in others.

So why does the UPC still require 18 inches of other than PEX piping on the inlet and the outside of the water heater. It’s easy, not every water heater has a built-in heat trap and the hot water migrates through the piping system. The water temperature is obviously hotter closer to the source.

The bigger issue with expansion tanks is the pressure in the tank is probably never properly set…

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…and more than likely NEVER had annual general maintenance performed, such as rechecking the pressure!

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