Expansion tank on hot water line? Cold

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Sbas

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Hi guys,

Had my plumber install my electric hot water heater. He installed it on the hot water line. From what I am reading online, most do it on the cold line but it doesn't really matter too much. Pros of the cold line are that it will have a longer lifespan.

Is this correct? Any issues with how it's installed?

Thanks!
 

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Jadnashua

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Not all ETs are designed for use with hot water, and their internal structure may not be designed for potable water use, either (being designed for hydronic space heating). But some can be used on either. Generally, one will last a lot longer when used on the cold, supply side.
 

ajaynejr

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In normal operation some water goes into the expansion tank each time a new tankful of water is heated. If the expansion tank is on the hot side, then the next time someone uses hot water, the now cooled water will come out of the expansion tank and head for the open faucet before fresh hot water from the heater tank gets up there, This lengthens the time and increases the water waste waiting for the water to get hot.
 

Penn

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Just wondering if a well pressure tank acts as an expansion tank? My electric hot water tank has never had an expansion tank and I have never had a problem. There is a check valve in the incoming water line from the well so no relief there. I am guessing the pressure tank has been acting as an expansion tank also.
 

Reach4

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Just wondering if a well pressure tank acts as an expansion tank? My electric hot water tank has never had an expansion tank and I have never had a problem. There is a check valve in the incoming water line from the well so no relief there. I am guessing the pressure tank has been acting as an expansion tank also.
It does. My system is that way.

In some special cases, a check valve is added after the pressure tank. In that case, you would need a thermal expansion tank. One motivation for such a check valve is to prevent backward flows through the softener from registering as water usage. Another would be to prevent hot water from going backwards thru the softener.
 

WorthFlorida

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Since it was installed with push and connect fittings or Sharkbite, it can easily be switched over to the cold side. The expansion tank pressure should be pressurized to the static pressure. The blader inside the tank (2.1 gal) will be only about a gallon of water when pressured by the water, as the water expands it may only be about a few cups of water additional depending on the inlet cold water temperature.

One advantaged as you set up is when the air pressure needs to be checked or the tank replaced, only the hot water will be turned off, not the entire home.

You can cut the CPVC or PEX at the tee off the hot pipe and get a Sharkbite Cap. Turn the elbow toward the cold water pipe and tee into it after the shut off valve. I just did this at my son's house. Normal house pressure was around 70 PSI but at times it was pressurizing up to 140 PSI and the T&P valve was opening. After the expansion tank the maximum pressure was down to 90 PSI. Why after 10 years the the T&P was opening suddenly we don't know.


IMG_6856.jpeg
 

LLigetfa

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Since it was installed with push and connect fittings or Sharkbite, it can easily be switched over to the cold side.
First off, the original post was from 2018 and just got dredged up. Second, moving the sharkbite to the cold side would put it before the shutoff valve.
 
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