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Thread: shut off tank when on vacation

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  1. #1

    Question shut off tank when on vacation

    My preference is to shut off a water heater and water when going away for a couple of days or more. Someone mentioned the cooling water would subject you to bacteria on your return. Would not turning the WH back on (say, set at 140 with a tempering valve) protect and "clean" your water in a few hours or overnight with that heat?

  2. #2
    Jack of all trades DonL's Avatar
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    I think it would be fine, and depend on your water quality.

    I turn mine off for a week at a time and have not gotten sick yet.

    Water in the pipes may be a bigger worry.


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    In the trades Dana's Avatar
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    The danger zone for legionella is storage temps between about 85F and 115F. Below 85F it just doesn't grow very quickly, nor above 115F. While it takes 140F to outright kill an established colony (and it takes days not hours at a mere 140F) it's very hard for a colony to get established even at 120F storage temps.

    So, when you go away for several days the temps will fall through the danger zone to some lower temp- usually below the zone except in the middle of summer in homes with a lot of solar gain and the air conditioning off. If the heater is located in a below-grade NJ basement it's unlikely to stagnate at 85F under any realistic weather & solar gain scenario.


    Seriously- every time you draw hot water water abandoned in the plumbing goes through the same cooling through the danger zone situation, and far more often than the turned-off tank does. In the rare instances where the distribution plumbing ends up being contaminated with established legionella colonies, the sterilization protocol is to purge with 160F water for something like a couple of hours.

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    DIY Senior Member guy48065's Avatar
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    I have a seasonal cottage that's unoccupied 90% of the year and the standard HWH is on "pilot" during that time. Mine is close to a worst-case scenario in that I'm on untreated well water from a 25-foot-deep well and I've had no problems with sickness, the runs (can't spell diarrhea), or any bad smells.

    A bonus: I was amazed to find that the water in my standard 40G gas water heater, with no extra insulation and in an uninsulated garage, stays hot enough with that little pilot flame to take a hot shower after it's been shut down for weeks. And I've always been told a standing pilot is a waste of energy ;-)
    Romeo and Atlanta, MI

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    In the trades Dana's Avatar
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    And a standing pilot IS a waste of energy. It's enough heat to pretty much balance the standby losses, but those standby losses are real. Most standing pilots on water tanks consume on the order of ~500,000 BTU per month give or take- you're talking 5-6 therms or 6+ gallons of propane per month for the convenience of having the water hot enough to use the instant you arrive.

    Recovery times from room temp is pretty reasonable for gas or propane fired tanks, so yeah, it really is kind a waste in a seasonal cottage only occupied 10% of the time.

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    Master Plumber Caduceus's Avatar
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    I could never recommend allowing a water heater to drop below the 120 deg.F. mark for any period of time. If you are gone for just a few days, what is the harm in leaving the tank stay as it is. It is unknown at any time how much legionella bacteria may exist in your public water system at any time. Typically there are low amounts of microrganisms depending on what type of chemicals are being used for water treatment and they have no affect on us because of the low concentration. But don't try to sell yourself into an idea that promotes a lack of safety, err on the side of caution.
    Some may say that they have never gotten sick from their hot water, but may have and not realized it. The symptoms are the same as the flu and may take just as long after exposure to show the symptoms. Children and the elderly are especially susceptible to the health risks when exposed. Rarely is ingestion of contaminated water a cause, unless aspirated. It is when taking a shower that it is inhaled with the vapors and settles in the lungs.
    The ideas that water sits in the pipes anyways and that temperatures drop in the tank when cold water is used are geared towards ignoring the core issue of safety with your water system.
    Just flush the pipes when you walk in the door and keep your tank at the normal operating temperature and you won't have to worry about Pasteurizing your tank or chlorinating the piping.

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