Water Heater Expansion tank

[MechGuy22]

Going to consult on a job tomorrow for a apartment building. The original engineer had designed the apartments with two water heaters, one on the 2nd floor and one on the first. He showed a "typical" detail of a electrical water heater with a expansion tank. So naturally the plumber installed two water heaters BOTH with expansion tanks. The problem is that the plumbing inspector is asking for the expansion tank on the 2nd floor to be removed because he doesen't want two expansion tanks on one potable water system..

Can ANYONE tell me why it would matter if there were two expansion tanks? I don't see any problem with there being two. In fact I think it should be required. Lets say there is a person that lives alone in the apartments perhaps an old guy. Old guys are always interested in saving a buck. If he shut the water heater valve off with the expansion tank upstairs because he never used that tank, and unplugged it, there were effectively be no path for thermal expansion at that point. Also, the plumbing code in my state (based off of the IBC) says nothing about having only one expansion device per system.

Any help or opinions would be MUCH! APPRECIATED!.

 

[MechGuy22]

Also, if there are heat traps installed on this water heater, which there should be, that would make both water heaters a closed system all the time and therefore I think they should be required on both in any case.

 

[Drazen]

Forbidding expansion tank for each water heater is opposite to common sense in my opinion, especially when heaters serve different users, having one for each tank should be good practice.

If your inspector is really stubborn and you have no option of questioning his decision, than it can be case of careful safety valve specifying.

Some codes do not require expanstion tanks for small heaters anyways, so the wors thing that can happen in practice would be frequent opening at safety valve.

I know at least one code that requires warning plate to be installed near safety valve, with text like "Do not shut off, leakage at safety valve is normal."

 

[chicopee]

If these two water heater have independent piping systems than two expansion tanks should be required independent of the source of make up water.

 

[MechEngNCPE]

Why would he not want 2 expansion tanks on the system, there is no reason not to.

 

[MechGuy22]

Thanks for the help everyone.

One thing I can't understand is if the water heater has factory installed thermal expansion nipples on the cold&hot, how would the expansion tank even do anything? The heat trap nipples basically function as a back flow device which closes the water heater off to the rest of the system, so basically when the water expands it wouldnt be able to go into the tank because the heat trap stops the passage of water. In my opinion the nipples should have some type of pressure bypass or they should be installed before the expansion tank.

Any opinions?