Watch! Performing a Multi-Inspector Home Inspection

Follow along as six InterNACHI® Certified Professional Inspectors CPI® in Texas perform a home inspection, a pool inspection, and an infrared inspection according to the Home Inspection Standards of Practice.

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11:29 the dude says you need an expansion tank because there is a PRV. An expansion tank is needed when there is a backflow preventer, which is commonly used with or part of the PRV.

According to the 2018 International Plumbing Code (IPC) section 608.3, tankless water heaters do not require a thermal [expansion tank] when no water storage device is used.**


Commonly but not always. So in my world, I do not consider the PRV when talking about a thermal expansion tank.

I do note the absence of a thermal tank and say something like this.

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/device as needed by a qualified plumbing contractor.

This was interesting an interesting blog conversation

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I call out the lack of an expansion tank when it is missing (about 80% of my inspections) but not on tankless water heaters.
If it wasn’t clear, that’s the point I was trying to make.

Also, he states that expansion tanks are needed “when there is a PRV”. That is not true. An expansion tank is called for when there is a backflow preventer (which makes a closed water system) and water storage. Many but not all residential PRV’s have a built in backflow preventer. And a tankless water heater does not have storage.


I agree and you are correct. Thanks for making that crucial statement. The presenters statement about the PRV also got my attention.

My takeaway. Tankless does not need a T-tank and a PRV should not be considered when recommending a t-tank unless you have extensive knowledge about the PRV installed on the subject property.

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