Two heaters, one expansion tank

[David Cortez]

Just finished a new home inspection. The home has a water pressure regulator installed. The house has two electric water heaters installed. However, only one has an expansion tank. Shouldn't there be an expansion tank installed on both? What am I missing? Thanks in advance for the help.

[Billy Stephens]

If they are in tandem one expansion tank.
* two supply lines 2 expansion tanks.
.

[Jim Luttrall]

Look at the rating for the tank and make sure the size of the expansion tank jives with the total size of the heaters if in tandem on the same system.
If the heaters are capable of being valved off to operate independently, then two tanks are needed IMHO.

[brianmiller]

Where do you guys typically find the water pressure regulator installed?

[David Cortez]

I've usually found them in line just after the water meter.
Thanks for the responses. These two water heaters are on oposite sides of the house, so I don't think they're in tandem. Since I can't tell without a doubt, I'll write it up. I do know that both of these were installed at seperate times, by at least a month, so the left hand might not have known what the right hand had done or why.

[Vern Heiler]

If the expansion device (could be a tank) is on the supply side of the valve, it can be anywhere in the system. I've seen them in the crawlspace no where near the water heater. The reason I stated "device" is because you may find an expansion relief in a toilet tank. There are several types of expansion device that can do the job. With a tank you do need to know the volume of the water heater/s to know if its large enough.

[Vern Heiler]

I've usually found them in line just after the water meter.
Thanks for the responses. These two water heaters are on oposite sides of the house, so I don't think they're in tandem. Since I can't tell without a doubt, I'll write it up. I do know that both of these were installed at seperate times, by at least a month, so the left hand might not have known what the right hand had done or why.

Be aware that an expansion device is only required on a closed system. Not all water meters create a closed system.

[Scott Patterson]

Where do you guys typically find the water pressure regulator installed?

Most of the time I find them right after the supply cutoff valve and with newer homes in my area this is usually near the water heater. I have found them in the crawlspace but I do not see them at the meter in my area.

Just about every home in my area needs a PRV. All of the local utilities put their water storage tanks up on the surrounding hill's 200' or more above the homes. It does produce a heck of an amount of pressure most of the time. Without as PRV the water at my home is 130lbs

[James Duffin]

At the CE class for my NC plumbing license this year the instructor reminded us that expansion tanks now have the same requirement as water heaters for backup drain pans. The instructor was a plumbing inspector and he said he is passing the installation where the expansion tank is mounted over the water heater so if the expansion tank leaks it will leak on the top of the water heater and run into the backup drain pan. He said he is also seeing more expansion tanks being put in the crawl space due to this requirement. This is in NC Plumbing Code....may not apply in your area.

[Ron Hasil]

If an expansion tank is installed in a crawl space, or anywhere in the system serving the water heater, it will not meet the code or manufacturer installation instructions. The expansion tank is to be installed after the supply shut off valve, and not to have any shut off valve after where it tees in. Code below is from the Illinois Plumbing code book.

Section 890.1220 Hot Water Supply and Distribution

C) A properly sized and approved expansion tank shall be
located on the outlet side of the check valve in the water heater's cold water
supply with no shut-off valve between the heater and expansion tank.