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Comment by soyelmango | Hacker News Reader

These kettles that keep water hot all day long seem very wasteful to me.

That said, does anyone know if it takes more electricity to reheat water than to maintain it at a given temperature?

Partly anecdotally and partly empirically: I have a Wattvision thingy on my meter, I use an electric kettle, and I cook lots of things sous vide (in water baths held between 130-160f for very long times). It appears to take drastically less energy to have a rice cooker keep 120 ounces of water at 150f for hours on end than it does to bring a kettle of water to a boil.

This makes sense to me. Watch the sous vide PID controller govern the rice cooker; it's only switched on for a fraction of a second every 10 seconds or so.

Water also has a high specific heat.

I looked into it when I bought one, and if I remember correctly a modern highly-insulated kettle uses much less power keeping water warm for 8 hours than constantly heating cold water. Of course, part of that equation is how many cups of tea you drink. And how hot you keep your water. Since I'm a white tea drinker, I keep my kettle on a low setting. I get much better results with a lower setting and a longer steep. (Part of the fun here is trying different teas, temps, and steep times)

    That said, does anyone know if it takes more electricity 
    to reheat water than to maintain it at a given temperature?

How long is a piece of string? It depends on how quickly your kettle loses heat, how warm the room is, and how long the interval between pours is. I have a generic Japanese thermos kettle, with vacuum insulated walls, so it holds heat fairly well.

It should be pretty easy to figure out precisely what the tradeoff point is with a datalogger and a thermocouple and some math, or a clamp ammeter and slightly less math.

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