Expansion Tank in Domestic WH

[Golestan]

Hi,
This may not be just the right forum, but please give me your openions:
Where should the expansion tank in a domstic water heating piping go? Before the water heater on the cold water line or after the heater (on hot water line)? Is the concept similar to heating water piping?

Also, at what size, in copper piping would you stop soldering (brazing). Can 4 inch or 6 inch copper be soldered, what is the preffered connection/joing means/ method?

Thanks,

 

[willard3]

If the expansion tank is on a recirc system, it will go on the negative side of the pump.

I specify 2.5" and up as welded; below 2.5" soldered.

 

[CptHk]

As far as pipe sizes go, I agree with willard3.

I have seen 4" soldered, and a few jobs I worked on needed some 4" soldered due to the nature of the renovation work required. The pipefitters/plumbers told me that even for the most experienced at sweating pipe, 4" is tough to do. There is just a much larger chance for a mistake. One of the 4" solder jobs did develop leaks within a month, which needed another shut down to fix the leak.

I have not seen 6" soldered.

 

[RossABQ]

With lead-free solders the joining of large copper is even worse (i.e., it's brazing). On a recent job, 25% of a compressed air system's joints >2" failed pressure test. Client will be using Sch 10 SS in the future.

 

[PEDARRIN2]

The expansion tank on a plumbing system should go on the upstream side of the water heater. There should be no check valves or bacflow preventors downstream of the expansion tank.

And if possible, there should be no valves downstream of the expansion tank as well.

I have seen 3" copper soldered. Above that, it is typically grooved pipe.

 

[PEDARRIN2]

I did not mention whether the expansion tank should be on the upstream or downstream side of the pump. I asked one of the more experienced engineers about this since I was unsure. He has never seen any problem doing it this way.

A domestic system is an open system in that it has to deal with the incoming service water pressure and the pressure being released when a faucet is opened.

A HVAC system, typically is a closed system, except for make up, so the expansion tank should be on the suction side of the pump. Otherwise you are just pumping against the diaphragm or bladder.

On a domestic system, typically the expansion tank is piped on the downstream side of the pump and you do get a little bit of give in the bladder from the pump head. But the main purpose of the expansion tank is to compenate for the expansion due to heating water against a closed valve, check valve, or backflow preventor upstream of the water heater.

This pressure increase will be more than what would be seen from a pump.

Also, it would be very difficult to pipe the system in such a way that the expansion tank is upstream of the pump and still be downstream of any valving upstream of the water heater.

I hope that helps.