Not saving energy

This is from Boris Johnson...

Please can we have competent people running the country, just some times?

So, let's explain...

  • An electric heating element, even in an old kettle, is 100% efficient at turning electricity in to heat. All the power used goes to heat. There is no "waste" due to being "inefficient" as waste is heat. [pedants: some very small part may go to light or sound]
  • Yes, some of the heat may not go directly in to the water - e.g. the body of the kettle, and the air. A more modern kettle may have a body that holds less energy, depending on the material (e.g. plastic not metal, etc). Again, this is a small part of what is used. Most goes in to the water.
  • Being "slow", so taking longer to boil, does not change that - it means that it is using less power (for longer time), but the total will be the same. There is an amount of energy needed to raise a volume of water by an amount of temperature - simple physics. The electrically energy is turned in to heat in the water. For the same volume of water getting hot by the same amount the energy used is the same.
  • Even if it was true (LOL), spending £20 to save £10 a year is hardly a newsworthy, or even useful, "tip" in this cost of living crisis - they seriously have no fucking clue do they?

What can help?

Old kettles used to have an element in the water at the bottom, and this had to be covered. It meant the minimum you could boil was more than one cup worth. This is wasted if only making one cup of coffee and leaving the water to go cold*.

New kettles often have an element in the base allowing you to only boil what you need, even if only one cup. That can cut down the power usage for each cup of coffee*.

* Such savings are less useful than they sound as that wasted energy, e.g. leaving a hot kettle of water to cool after making only one cup of coffee - ends up heating your house anyway. It is power used for something useful. It may not be as cheap as gas central heating or overnight storage heating, but it is power used to heat your house, so not entirely wasted in winter.

P.S. It gets worse!

If the walls are well enough insulated, which they should be in a modern house, this makes fuck all difference. Yet again, a basically lack of understanding, and yet again a total waste of time against the costs families are facing, they are fighting fire with water pistols, no - with eye droppers, empty eye droppers!


  1. True that energy is energy, but there are kettles that can significantly reduce energy consumption through configurable target temperature and improved insulation. For example https://hubimex.co.uk/hubimex-thermos-electric-kettle-v4-1-5l-steel/

  2. If a kettle takes longer to boil, then it is holding water at a high temperature for longer during the boiling process, which means that a greater amount of heat would be lost to the environment (since the rate of heat transfer is proportional to the difference in temperature).

    However I would expect this effect to be very minor, since the amount of heat lost during boiling ought to be a very small proportion of the total energy required to boil the water. You would save more energy by having a better insulated kettle, boiling less water, or boiling it to a lower final temperature. Perhaps it is these latter qualities which lie behind the claims that a newer kettle will save energy?

    1. Not saying some aspects of newer kettles do not help at all. But the impact will be very minor at best, and *any* saving in "wasted" energy is tempered by the fact that wasted energy heats you home.

  3. He's a buffoon in any case. The best way to save is to get one of the "instant" one cup kettles so you boils exactly what you want or a kettle on the gas hob might be cheaper as gas is cheaper?
    Or i suppose i could break out the Kelly Kettle and use that, just need some dry twigs, no electric or gas.

  4. The other issue is auto shut off. It seems many kettles are all made the same now, where a pipe inside the kettle funnels steam down to a bimetallic switch in the base. This means in order to automatically shut the kettle off, enough steam pressure needs to build up inside the kettle to force heat/steam down the tube to heat the bimetallic switch. It seems to take a good number of seconds (~15 with our current kettle) for this process to take place, and I've seen varying delays with all makes of kettles. The bimetallic strip isn't reacting to the boiling point of water, just reacting to warmer air/stream arriving due to the boiling water applying enough pressure to overcome what is leaving out the spout to slowly move heat into the base. An interesting video by Steve Mould shows this in action https://www.youtube.com/watch?v=VzqN4Cn8r3U where a kettle will turn off with boiling alcohol, even though that boils at quite a bit less than 100 degrees. We had a previous kettle using some electronic switch that switched off immediately it started boiling, but our current one we always intercept and switch it off manually, as otherwise it just boils madly for too long before it switches off. Given a single cup kettle boils very quickly, this extra boiling before auto cut out is a considerable percentage increase of power used, and I suspect most people don’t consider the kettle really boiled until they wait for it cut off by itself.


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