Expansion Tank Installation Questions / Opnions

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Mr.T

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I'm installing a brand new expansion tank on my fully re-piped system. My current plan is to install the tank right after the incoming city water service. Although I started to rethink this for a few reasons. As you'll see in the pictures, everything else is basically completed (PRV, Water heater, shut-offs, etc.).

1) Water heater is approximately 20 feet away from where I plan to install the expansion tank. There are various tees and also the heater cold inlet shut-off between the tank and the heater. Am I making a bad decision by mounting it where I planned vs right near the water heater?

2) Current location would put the tank right above where the future water meter will be (city provided PVC pipe template in the picture). Am I being overly worried about the risk of the tank failing/filling/falling on the meter if it were to be dropped during an R&R?

3) Is there any reason NOT to put a shut-off valve on the expansion tank line to aid in future R&R if needed?

If there is anything else that looks wrong/bad practice please feel free to comment. I have thick skin and want to do this all correctly.

Thank you!

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hj

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Theoretically, an expansion tank can be anywhere in the system. Practically, it makes more sense at the water heater AFTER the heater's cold water shut off valve.
 

wwhitney

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No personal experience with expansion tanks, but the idea is to have an unimpeded water path between the tank and the water heater. So I would think you'd put it by the water heater, between the cold shutoff and the hot shutoff. That allows you to service the expansion tank or the water heater without draining the pipes.

In particular, I would think a valve between the water heater and the expansion tank would be a bad idea, as if it gets closed, the tank can't do its job.

Cheers, Wayne
 

Terry

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I have an expansion tank in the garage on the incoming cold line, not near the water heater at all. It still works in that location.
Normally I install them at the water heater during a new install.
 

Mr.T

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Thank you all. What I started to debate was how important it is to have the tank closer to the "source" in terms of functionality. I guess I'm in one of those situations where I probably chose a location that will work in terms of the rules, but perhaps is not ideal compared to standard practice. Admittedly, I recognized the need for the tank AFTER I had already piped in the water heater.

HJ,
When you say AFTER the shut-off, I interpret that as between the shut-off and the heater.

Wayne,
I do agree that there is always the risk of having it accidentally shut-off thereby rendering it useless, but I feel like the risk is generally minimal.
 

Reach4

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It is best to have the expansion tank somewhere after the softener, because otherwise that bi-directional flow through the softener to/from the tank results in a bit of phantom flow recorded by the meter in the softener.

That said, most people with wells and pressure tanks don't have thermal expansion tanks. The pressure tank acts like a giant expansion tank. But if phantom flow were deemed to be significant enough, then the there would be a check valve after the softener, and a thermal expansion tank would be after that. I don't consider my phantom flow to be at all significant.

I do agree that there is always the risk of having it accidentally shut-off thereby rendering it useless, but I feel like the risk is generally minimal.
When you shut off the water, you should also shut off the WH.
 

Mr.T

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Reach4,
Just to clarify, this expansion tank is only on my incoming city water line (not my separate well water system). So there is no softener that I need to worry about. The city water is what will be heated.

Also, My plan was to put a shut-off in the white pex line after the tee and before expansion tank so that if needed in the future, it could easily be isolated and removed without shutting off and draining down the system. Does that make sense?
 

Reach4

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Just to clarify, this expansion tank is only on my incoming city water line (not my separate well water system). So there is no softener that I need to worry about. The city water is what will be heated.
Yeah, I was just talking general tank philosophy, trivia, etc.
Also, My plan was to put a shut-off in the white pex line after the tee and before expansion tank so that if needed in the future, it could easily be isolated and removed without shutting off and draining down the system. Does that make sense?
Yes. Your plan makes good sense.

Air precharge should be set to match the normal incoming pressure. So if no expansion, then the tank is empty of water. Air precharge is measured and set when the water pressure is zero.

Knock on your empty tank, and remember what that sounds like. If your tank gets water in it, it will sound different.
 

Mr.T

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Yeah, I was just talking general tank philosophy, trivia, etc.

Yes. Your plan makes good sense.

Air precharge should be set to match the normal incoming pressure. So if no expansion, then the tank is empty of water. Air precharge is measured and set when the water pressure is zero.

Knock on your empty tank, and remember what that sounds like. If your tank gets water in it, it will sound different.

- I set the pre-charge exactly as you described. (set to 60 psi which is what my PRV is set to). Glad I did it right. Good idea on the empty tank sound. I'll do that.
 
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