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I need to replace an electric hot water tank (it has started to leak). I'd like to replace it with a used one because the property, which has 2 occupied units, is for sale and it is expected to be torn down.

I do not want to put the tenants at risk and I recognize the safest / easiest / fastest solution is to buy new (which may be the route I take) but this question is meant to understand if, and how, the risk of a used used tank water heater can be mitigated. It seems it should be possible to accomplish this goal.

I can find used ones online (at all kinds of prices) and I have come to understand that the concerns around used tanks are, in general, build up of bacteria, rust and calcium.

1 RUST Not being familiar with heater tanks, I'm not sure where to be looking for rust other than connections and the bottom of the unit. Are there other locations I should look at? I assume the main issue with rust, if found, is the impact on the remaining life of the unit rather than health concerns. Is that correct or are there health / other issues with rust?

2 CALCIUM My understanding of calcium build up is that either vinegar or a specific cleaner (based on the tank's composition) can be used to help remove it. Is this correct and if so is calcium a barrier to a used unit? Or is there something more to calcium build up that is a concern?

3 BACTERIA From what I've read, the most serious concern is bacteria which causes legionnaires disease. The approach seems to be to ensure the temperature setting is correct - somewhere between too hot (scalding) and too low (bacteria-friendly). Will a high temperature (temporarily) kill any bacteria? If not is there another way to ensure that the water is safe?

Since most tanks that I've seen online are disconnected and ready for sale, my last concern lies with whether the above problems are exacerbated if the tank still has water in it or has been dried out for a year or more.

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Look at the anode rod, the condition of which would tell you a lot about how much of a problem rust is likely to be. Rust, and the ensuing leaks, is the big concern. If it's detieriorated but not gone, replace it. If it's gone, pass on the tank.

Calcium is pretty much a non-issue, as it can be removed.

Depending how short your short-term concern before sale and teardown is, simply the age of the heater (say, 5 years or less) and no evidence of leaking might do for a used one. 10 years is a "typical ballpark" for the short end of life on electric heaters - you may have more locally relevant information by considering the present age of the one that's now leaking.

Bacteria is a matter of temperature. You can also give the thing a (diluted) bleach flush before putting it in service if you have issues with it being used.

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  • A few hours at 140°F+ should kill any bacteria present in the tank. Then the temp can be turned down to a more reasonable 120°F or so. Of course, many tanks do not have an actual temp scale but just "warmer/cooler/vacation" type of scale (which is useless), so a thermometer held under the hot water at the closest tap can be used for determining water temp. If it's 140° at the tap, it's > 140° in the tank.
    – FreeMan
    Aug 31, 2023 at 15:24
  • This response has confirmed my thoughts on the idea. My guess is this approach is reasonable for a homeowner/diyer to pursue but may not be a cost/time/labor effective solution for a professional plumber. I'm looking into some used options and will update my experience here asap. Thanks for the quick reply.
    – Ric
    Sep 1, 2023 at 15:33
  • Disappointingly I could not source a local electric heater that was ~200L in a suitable time so I've had to purchase new. The response was helpful in understanding the concerns of installing a used water heater.
    – Ric
    Sep 8, 2023 at 17:32

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