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Old 06-18-2008, 08:42 AM   #1
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Hot water heater expansion tank?

My local water company installed a new meter and a check valve on my incoming water line. Now my TP valve weeps; Older house without an expansion tank. Because of the check valve I know I need to install an expansion tank. The installations I have seen have the tank on the cold water inlet. Due to my piping configuration, it would be hard to install on the cold side and a snap to install on the hot side. Question: is installation on the cold side neccessary or does it make no difference?


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Old 06-18-2008, 08:50 AM   #2
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I've seen them on the hot side once before, but we always install them on the cold. I'm not honestly sure why, though. Hopefully someone else will pipe in and learn me.


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Old 06-18-2008, 09:27 AM   #3
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If instructions say cold side then thats where is needs to go, however I seen them on the hot side also, only thing is, if you don't follow installation instructions, and it fails, you void the warranty of said product.
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Old 06-21-2008, 10:53 AM   #4
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Cold side is best. I have seen a few instances where a tank installed on the hot side caused the heated water to be pushed back into the cold side. (That one was fun to diagnose). The tank works by compressing an air bladder to absorb excess water pressure. When a cold faucet was opened the pressure was relieved and the bladder expanded, forcing the extra water back through the path of least resistance, the water heater. This in turn forced hot water back up the cold inlet to the water heater. This is admittedly very rare and all the planets have to be in line for it to happen but I have never known of a problem with the tank installed on the cold side.

One other thing. If at all possible, install the tank with the opening facing down. This will help prevent sediment and scale from collecting in the tank and reducing it's effectiveness.

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Last edited by mstplumber; 06-21-2008 at 10:54 AM. Reason: typo
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