The kettle that beats the stock market!

The one I bought is slightly more modern than this (credit)

(Don’t worry, I haven’t gone completely barmy, there is some logic behind that title.)

This is one of those things where I offhandedly thought about something and then got stuck in the rabbit hole of my own creation trying to work what the actual answer was and if it was at all relevant in the grander scheme of things. The answer to the question you don’t know yet turned out to be kinda interesting, so here I am sharing my findings with you and why I opted to go buy a new kettle.

I swear I’m sane. Bear with me.

How much does it cost to run your kettle to make a cup of tea?

It’s a surprisingly simple calculation once I google’d the right words:

(# of litres of water X temperature change X 4.2) X (electricity rate in p / 1000)

Or if you’d prefer that with some actual numbers, assume the following:

  • My old kettle had a minimum fill of 1 litre, so we use 1 here
  • Roughly, water is at room temperature of 15 degrees Celsius and we’re heating it up to boiling, otherwise known as 100 degrees Celsius
  • 4.2 is the specific heat capacity of water (how much energy you have to put into it to make its temperature increase)
  • And my electricity rate is 15p

Put it all together and you get the following:

(1 litre X (100 – 15 degrees) X 4.2) X 0.015 = 357 watts X 0.015 = 5.4p

Thank you Xailter, my life is now complete

The story doesn’t end there though. I was actually looking into whether a kettle existed that let you modify its power draw. Most kettles pull about 3000W (3kW) through the plug to boil the kettle as fast as possible. I was thinking that if I could limit the power draw to about 1000W then I could basically boil my kettle for ‘free’ from my solar panels. During winter, they don’t produce a whole lot more than that.

Turns out that is not a thing that exists.

But I did stumble upon a breed of kettles that let you change the temperature the kettle will stop heating at. I never knew this was a thing! Even better, these kettles let you boil an incredibly small amount of water as a minimum, instead of the whole 1 litre I had to boil each time which mostly got wasted! I had to experiment further.

So here’s my new kettle

A thing of beauty, no? (link to buy – I paid £54 for mine)

Why is this relevant? The main points here are:

  • You can boil a minimum of 250ml compared to my old one’s 1 litre minimum
  • You can choose the water temperature from: 70/80/90/100 degrees Celcius

Before, if I wanted a brew, I burnt through 357 watts to get the hot water I wanted to enjoy my delicious cup of tea. If instead I’m heating the bare minimum to get my hot water and I’m only heating it to the temperature I want, then the inputs to the equation change and it now looks like this:

(0.25 litres X (70 – 15 degrees) X 4.2) X 0.015 = 58 watts X 0.015 = 0.9p

Or an energy saving of 6.0x the amount of electricity! Damn, I didn’t expect it to be that good! In reality though, I’ve found coffee at 70 degrees to taste… not great, but I can’t tell much of a difference on the 80 degree setting. That is still a 5.3x saving win over the old kettle.

So you can retire tomorrow then on your savings?

No, of course not. My wife or I probably boil the kettle 5-6 times a day; we’re real tea/coffee/hot chocolate fiends. A 4p saving each time isn’t much on its own, but add it up over the lifetime of the kettle and it will basically pay for itself, assuming your old kettle was an old crap one like mine. For example, assume I boil the kettle 3 times a day for a year (not an unreasonable assumption in an average household) up to 80 degrees:

3 times a day X 365 days a year X (5.4p – 1.02p (80 degree cost)) = £47.96

My new kettle cost £54 from Argos (no idea why the price is so high now). Even if we assume you only save half the amount above (boiling 500ml instead for two people all the time), the kettle easily pays for itself in 2 years. After that you’re home free and up on the deal. Who doesn’t want an ROI (Return on Investment) of over 50%?!

Oddly the best thing is, I haven’t even changed a habit. Put water in kettle, up to the line. Put kettle on, make sure it’s set to 80 degrees. Enjoy delicious beverage. Easy. Everyone can start doing this right now and enjoy the savings and you have to change nothing in your life.

Of course, ASDA has a cheaper one (link to buy)

Oh and if the above price put you off, don’t worry. ASDA has a similar one for just £30. What are you waiting for?!

And now you know why I bought a new kettle.

6 thoughts on “The kettle that beats the stock market!

  1. I’ve never seen such enthusiasm for a kettle haha! Interesting discussion though, I’ve never even thought about mine except for what colour it should be.

    Liked by 1 person

    • Hi Brian, thanks for the link. I was aware travel kettles existed – what I was looking for was a kettle where you can change the amount of power it draws, e.g. set the kettle to draw either 500 / 1000 / 2000 / 3000W manually. Alas, that doesn’t seem to be a product that exists 🙂 The variable temperature controlled ones are a good second place choice though.


      • Sorry, that maths looks a bit dodgy to me too – 0.015 is 1.5 pence, not 15p i.e. 15p is £0.15 still trying to get my head around the rest – been a long time since I was at school & I worked in j/kg/degC
        As for varying the power input, easiest is to put a (powerful enough) dimmer switch in circuit – but not really practical 🙂
        p.s. why does your comments box insist on the website field being filled in? (I don’t have one)


  2. Ahh, you’re too stuck in the problem to see the simple solution!! 🙂

    I did the exact same Maths and was shocked at the >5p per boil of our kettle so I’ve been boiling water in a small saucepan for my morning coffee for the past year. The cost was reduced to something like 1/10 of a penny per boil.

    Of course, this isn’t saving the environment much. I’d love to install a wood-burning stove.

    Liked by 1 person

  3. Actually, the 5.4p cost is wrong, didn’t sound right to me – if it was correct the the 3kW kettle would take almost 7 minutes to boil that litre of water, actually should take less than half that.
    I’ve worked it out to about 2.7 pence, however, don’t ask me to show the working, as I’ve been round so many (metaphorical) houses that I’m quite lost, I *think* your error is somewhere in converting from joules to kWh.
    on another note, how many kWh can you buy with the cost of your kettle? (£54 would make a lot of cups of tea) – would the ketle even use £54 worth of Electric during it’s lifetime?


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