Science Hour…

Since starting the Great Energy Race, I feel a little like I have asked more questions than I have answered.
Having already amazed you all with my slow cooker maths, I thought I would dazzle you all with science, and test a theory….
I am going to take you all back to your secondary school science lessons and Conduct an Experiment.

It is more energy efficient to boil 3 mugs of water all at once, and then store the excess in a thermos for tea later in the day, than it is to boil the one mugs worth of water, three times
If I remember correctly, I should have a Null Hypothesis too, but it always confused the heck out of me, so I’m not doing it. Mark me down.


GERace kettle1

  • Electric Kettle
  • Clock with second hand
  • Mug
  • Water
  • Thermos flask
  • Calculator


  • Fill mug with water
  • Decant into empty kettle
  • Press switch to start kettle
  • Note time
  • Allow kettle to boil, and note the time that it stops at
  • Make tea and drink
  • Next time tea is needed, fill mug with water
  • Decant into empty kettle
  • Repeat twice more (3 mugs of water in total)
  • Press switch to start kettle
  • Note time
  • Allow kettle to boil, and note the time that it stops at
  • Make tea, and fill thermos with remaining water


  • Time for kettle to boil one mug of water: 75 seconds
  • Time for kettle to boil three mugs of water: 160 seconds (53.33s per mug)

As you can see, I have conclusively, without a shadow of a doubt, and with a greater than 95% significance (again, I remember that being important, can’t quite remember why now-something to do with confidence intervals..?) that the most frugal, energy savvy way to boil water for tea, is to boil more than you need, BUT only if you then store the excess in a thermos for subsequent cups of tea.

Hurray for science 🙂

PS. Rest assured that I wore a white coat and safety specs throughout proceedings…

Kettle and pud2

19 thoughts on “Science Hour…

  1. I use a teapot & cosy as I enjoy more than one cup, it stays hot enough to last me through a film & saves me popping out to the kitchen during the adverts to “put the kettle on”. Breakfast wouldn’t be the same either & it means using fewer tea bags too.

    • It’s not too bad if you use the hot water to make fresh tea each time, rather than make a flask of tea, which I agree, is not that nice!

  2. It would also be interesting to know how much energy each scenario uses. After Lent I will invest in an energy reader thingy and get the kids to do it as an experiment. I’d also like to throw in something like ‘how much energy does it take to heat a mug of water in the microwave’ or ‘how much energy does it take to boil the equivalent on the hob’ (though as we have a gas stove I don’t know how one would do that).

  3. I like this theory but drawbacks are
    Don’t have a flask so expense involved, few seconds of energy v new flask
    I like a fresh piping hot cuppa so will the water stay hot enough?

    • If you are lucky Kate, you might be able to pick up a thermos on Freecycle, or failing that the charity shop, so certainly not mega bucks. The water certainly stays hot enough for ‘piping hot’ for a couple of hours-guess it depends how much tea you get through!

  4. I’m sure Jen will answer later but I read it that you put a mugful of water from the thermos back in the kettle so it will be as hot as usual but starting from very hot so using less energy.
    It’s worth remembering to heat the inside of the thermos a bit first.

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