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Tanklets > To Drain or Not to Drain

Q: Hi.  I heat my water with oil during the winter time.  I heat the water in an electric water heater during the summer.   I am wondering whether or not I should drain my water heater for the winter. 
Would it rust more or less with water in the tank?  I've been draining it, and not sure if I'm doing the right thing.

I assume that even if I left the water in the tank, I'd have to drain and fill before starting it up.  (Legionella?) Any other Legionella aspects? Thanks very much for your expertise.  It's hard to find anything about this on the web.

A1: If you drain it, the sacrificial anode can no longer function, yet the environment will still be quite moist, so exposed steel in the interior will rust. If the tank isn't powered up, there is no legionella risk. That likes heat. You might, however, want to pour a couple of pints of drugstore peroxide into it to eliminate stagnation odor. -- Randy

A2: Hello:  there are things to balance.  A benefit of keeping a tank full of water is that the anode can then protect the tank and keep it from rusting.  Balancing this with bacterial concerns is not too hard.  I'd find a way to put either hydrogen peroxide (preferred) or bleach into the tank when shutting it down, and then drain and flush the tank again on start up.  Alternately, if you drain and COMPLETELY dry the inside of the tank, that can work also. -- Larry

Q: Thanks. It sounds like I probably should keep water in it when storing. I didn't know that Legionella required warm water-I thought room temperature would do it. (I've got well water, not chlorinated.)

A2: Hello:  The bacteria go dormant at 68F and lower.  They aren't killed off, but they don't multiply either.  With these bugs, it's a matter of dose.  You don't want to inhale too many at once.  So, if your stored water will be in that range, you're good. -- Larry (4/1/2016)

Q: I recently installed a new gas water heater with your recommended retrofits (two anode rods, curved dip tube, ball valve, heat traps) in my house that I don't currently live in and am renovating. Maybe once every 6 months a guest will use the house but otherwise I turn off the gas and water supply to the water heater. The question I have is whether I should leave the water heater full of water or drain it during long (6 months or more) periods of inactivity? If I drain it and the residual water level is below the longest anode rod will there be the possibility of rusting if the glass lining is compromised? Thanks for your help.

A: Hello: The problem is double edged. The tank is best protected from rust by being full of water with the anode working correctly. A partly filled tank is not protected. Draining the tank can work if the tank is completely dry and stays that way. Leaving a tank unused for six months, full of water could give you a really stinky mess -- Larry (9/6/10)

Q1: Thanks Larry for the insight. I then have two other scenarios for you to comment on: 1) Would leaving a hot water tap open on an upper floor with a full water tank be beneficial? 2) Would leaving the gas and water supplies on and just running the pilot light be a good idea? I know from experience that just a pilot light will maintain quite a bit of the temperature of a full tank if it is not emptied frequently.

Q: We leave our mobile home in Florida for the summer. We turn off the water and drain the tank after turning off the electric power to it. Once when it was turned on again in the fall, it leaked seriously and we had to replace it. Is there a necessary procedure to follow on power up?

A: Hello: That tank may have leaked because it's time had come or because the tank remained wet inside and rusted while you were away. Any tank stored empty needs to be made as dry as possible to stop or slow rusting. Unless there were a serious water pressure problem, I would not expect filling to cause damage. Do make sure power is kept off to the heater until you have a good solid stream of water running from the tap.-- Larry (9/6/10)