Is not having a expansion tank a defect?

Do you call out a Hot water heater without an expansion tank as a defect?

It depends. If the PRV(pressure reducing valve) is on the supply line for the water heater or if a back flow preventer is on the line an expansion tank or valve is needed since it is now a closed system with this devices installed on the supply line. Keep in mind that most new water meters have built-in back flow devices that you will not be able to see… We always not the absence of an expansion tank or valve and recommend them.


Only if it’s required by your local jurisdiction. Otherwise, no, it’s not a “defect.”

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They are required for all new installs in my area so I call them out if not installed, new or old. More than anything so the client knows what to look for when they get a new WH installed, same goes for WH drain pans.


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Wondering… what is a Hot water heater? Isn’t the water hot already?
Just asking :rofl:

Here you go Douglas


Thank You, sir

Thank You Sir

Thank you sir

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I do not. I would need more information about the water supply system before I called out the lack of an expansion tank as a defect.

An expansion tank is not the only method of controlling thermal expansion.


Allthe new installations in my area require them. Older installs don’t. The determinent has to do with the water entry setup as Scott answered. If i don’t see one I don’t call it out as it is usually not a problem.

First where are you located? For some it may be a local or State issue.

Here in Texas we are required by the State mandated SOP to call out a missing expansion tank when a PRV is installed. As I have previously stated, regardless of what Texas or others may say, Texas does use the IRC as a guide and this is covered in section P2903.4.1 (2018 code version).

What is interesting is that many if not all of the common PRV’s we see here (and possibly in your area) are designed with integral bypass valves to mitigate this issue. One example of a common PRV is the Watts LFN45B which you can read about HERE . These are “listed and labeled” valves.

Also what is interesting is we have a large municipality here that specifically requires PRV’s on all new systems but does not require expansion tanks. Also in that jurisdiction they are unable to fully control the supply pressure and is why they require PRV’s. I’ve measured water pressures as high as 165+ PSI on homes without PRV’s and the integral bypass feature of the PRV would not help.

So whether you choose to call it out or not, if not required, be sure to have your reasoning ready if it is challenged later.


This is what I say when there is no tank/device.

Water heater did not have a visible thermal expansion tank or device which is recommended for a “closed water system”. I was unable to conclusively determine if the water supply was an “open or closed” system and such determination is outside our standards of practice. Thermal expansion can create a rapid and dangerous pressure increase in the water. Recommend further evaluation and the installation of a thermal expansion tank or device as needed by a qualified plumbing contractor.

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In other words you state the truth and put it back on the client to ignore it if that’s what they choose. Nothing wrong with basically saying you don’t know (“unable to conclusively determine”) and I do it plenty! Worst thing is to try being BMOC as that gets us into trouble.

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Do you have an expansion tank on your own water heater?

Awesome thanks Brian

I don’t, unless a backflow or pressure reducing valve is also present. We have millions of homes without any of this stuff, that continue to work just fine. The city water lines can easily handle a little bit of thermal expansion flow: there’s no actual problem.

I do call it out for solar thermal systems, due to much higher tank volumes.
I see incorrectly sized thermal tanks, which is almost worse than having none.

No tank, but it has a thermal expansion valve that drips once in a while to relive the pressure on the supply line. Sometimes, this valve is installed inside a toilet tank! Does the exact same thing.

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Do you have a picture of one of these thermal expansion valves? I don’t think I’ve ever seen one in my area. Just curious

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Most common that I see…

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