Some things you are not meant to know

This is, I hope, the last chapter in the water-heater debacle. Cue Ed McMahon: “How … hot … IS IT?”

Well, it’s like this: today, it’s apparently considered bad form to put any kind of actual numbers on the control knob. There’s a dot, and there’s the word “VACATION” about 180 degrees away from it. Nowhere will you find 180 actual Fahrenheit-approved degrees, which is too hot anyway. In the US, everybody says 120. The Canadians beg to differ:

To reduce the risk of burns from hot tap water, the temperature setting on the water heater can be turned down. But if the temperature is set too low, bacteria may begin to grow in the tank. Even at 60°C — the setting on most electric water heaters — an estimated 25% of all water heaters are contaminated by legionella bacteria.

Legionella bacteria tend to grow in the lower temperatures at the bottom of water heater; such bacteria can cause a form of pneumonia. The organism is generally transmitted when people inhale contaminated water droplets from whirlpool baths, showers or building air conditioning systems. In Québec, about 100 people a year are hospitalized for pneumonia caused by contaminated residential water heaters.

In light of the statistics, it is not advisable to lower the water heater temperature to, say, 49°C. This would not only reduce the hot water supply by some 20%, it would also put your household at risk of contracting pneumonia.

Forty-nine degrees Celsius is — guess what? — 120°F.

So I feel much better with my estimated 140°F (60°C) setting. Admittedly, this would be considered a seat-of-the-pants estimate if pants were involved, which they are not. My criterion, using my current single-knob shower, is this: “With the knob turned all the way up, does it seem like it’s almost too hot?” If so, the setting is correct. It reminds me somehow of P. J. O’Rourke’s advice on steak in an iron skillet: “As soon as you think the steak should cook just a little longer, stop cooking it.” This, of course, assumes the steak is as thick as the heel of a Bass Weejun.


  1. McGehee »

    7 February 2016 · 8:02 am

    In our old house I routinely kept our water heater set as high as possible, simply because it wasn’t just a water reservoir, but a heat reservoir. The more the new water could be heated simply by being infused into the tank, the less additional heating it would need to get up to temperature. Meanwhile there’s plenty of cold water to leaven the hot, which would also help conserve the water in the tank.

    I’m not sure whether the logic actually works, but I think I’ll go make sure our new tank is set as high as possible.

    And if 160° is hot enough to keep bacteria out, I’ll stop worrying about the default 192° setting in the heating crucible of my Keurig brewer being short of boiling.

  2. fillyjonk »

    7 February 2016 · 1:16 pm

    I’ve alternately heard the lower temperature is recommended to save energy or “for the children” (so they don’t scald themselves.)

    I dunno. No children darken the door of my house, and in a lot of other ways I tend to save energy (too busy with work to drive very far, for one thing), so I’d rather have a marginally-better-at-killing-bacteria temperature.

    (I had to get in there with a flashlight and check mine: yup, it just says “HOT,” “WARM” and “VACATION” I have never bothered to turn it to “VACATION.”)

  3. McGehee »

    7 February 2016 · 1:55 pm

    I keep mine one notch under “Mythbusters episode.”

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