I see them on nearly every new home in Charlotte, NC. Must be code there. Been told that the county I live in now requires them also.
I recommend them for all homes on municipal water systems and attach this useful article for the client’s information. The article link is below.
P.S. We must remember that we are not ‘code inspectors’. The home has already had that done. The code is the minimum expectation. I often make recommendations that exceed code. And the home inspection report should not be taken to be a “repair list”. Start recommending things that exceed code and you’ll have to remind agents of what our role is, but it’s what we should be doing as a service to our clients.
Good link Joe, interesting reading.
An expansion tank must always be installed in order to prevent the excessive pressure in the water when the water heater is connected to any closed system. Also you need to check the valve regularly.