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Question DetailsAsked on 9/2/2014

We have well water. We don't have an expansion tank now. We are going to replace water heater. Do we need an expa

Do we need an expansion tank if we have well?

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1 Answer


Theoretically, depends on length of piping in the water system, etc.

However, from a practical standpoint, unless you already have an air expansion tank at the pump/wellhouse (commonly about 30-60 gallon vertical tank) that is NOT blocked from the water heater by a backflow preventer, then yes - it is cheap insurance against flooding due to a blow-off by the overpressure valve or a broken/leaking pipe, which by Murphy's Law always occurs the minute you leave the house for an extended period of time or vacation. Well worth the extra $100-250 it should cost if done concurrent with water heater installation, depending on your local code requirements for type and size.

The reason you probably should put one in is the same as on houses with city water with backflow preventers - the footvalve on the well suction line or bottom of the submersible pump prevents waer from flowing back into the well, but also acts as a backflow preventer from the house, so the heating water expands and pressures up the entire water system when there is no hot water usage, and for a full tank of cold water coming up to temperature, say after a lot of clothes washing or bath or long shower, can cause enough expansion to damage the piping or tank.

BTW - if you have a large tank that looks sort of like a galvanized water tank near your pump or well, do not just assume it is an air tank - might be an air trap (typically 5 gallon or less in size) to remove air from the system (especially with centrifugal or jet pumps), or a sand filter. If an expansion tank if will sound mostly hollow in normal use if you tap it with a tool, and if you run your hand up the side only the bottom third or less should be cold - the rest should be warmer than the bottom, as that is where the air expansion pocket is. Should also be labelled as an expansion tank or chamber.

Answered 6 years ago by LCD

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