MoneySavingExpert Chair, Martin Lewis · Editor, Marcus Herbert

# What does it REALLY cost to run your energy guzzling household appliances? (Less than you think)

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On another forum, I saw a heartbreaking post from someone who told us they were going to give up heating food to save money.  Raw food only from now on.

This really brought me up short.  I already knew that many people are the wrong side of the breadline, with not enough money to live on.  However, I did feel that this post was based on not understanding how much it costs to cook food, and this led me to think a lot further about what it costs to run household appliances - especially what it costs to cook food.

I want to know this in order to be able to reassure people to whom pennies make a difference what it actually costs to use their appliances.

So I started to do some maths.  And I found that virtually all the sites I found agreed with my maths.  But here's the kicker - WE WERE ALL WRONG.  The wrong sites are still out there - sites like How Much Electricity Does a Slow Cooker Use in the UK? - Chef's Pick (chefspick.co.uk)

So here are the questions.  I want your help with number 3, good people of MSE.  If you want to discuss questions 1 and 2, the floor is yours.

1. What was my maths?
2. Why was I wrong?
3. What are the real costs of running electrical appliances - and let's focus on the ones used to heat food, as a starter?

I reserve the right to add further questions!

QUESTION 1.

First I found out what a kilowatt hour costs.  I thought that https://www.nimblefins.co.uk/average-cost-electricity-kwh... was a good listing, shows different regions of the country, and looks pretty up to date. Let me know if you think I was wrong.  So I will use 29p as the cost of a kWh.  So far so good.

Then I looked at the wattage of the appliance I was considering.  For example, and let’s keep it simple, a small slow cooker is 100w.  (A large one is about 1.7Kw)

So then I made my Big Mistake.  ‘OK’, I thought.  If a SC (for example) is 100w, that means it will use a Kw in 10 hours. (No-one is likely to use it for that long, but as I said, let’s keep it simple.)  So cooking a stew in this little machine for 10 hours will cost a kWh – 29p.  Job done.

QUESTION 2.

I WAS WRONG!  I was actually surprised that it cost that much, and rightly so.

If you listen to a slow cooker cooking (or a hob heating up, or an oven) you can actually hear it switching itself on and off as the thermostat kicks in.  If it’s a gas oven, you can see the flames adjusting their size.  My 100w slow cooker does not draw 100w consistently.  A simple model will just turn itself on and off to maintain the temperature and not overheat.

A 100w appliance will not draw more than 100w (ok, it may have a 10% tolerance) so if it has a thermostat, it is obviously drawing a whole lot less than 100w an hour.  In fact, once the crockpot gets up to temperature, it will draw hardly any energy – it just needs to maintain that heat. (And yes, I appreciate that it might be a good idea to transfer the pot to a hay box once it’s hot, and I will be passing on this idea too.)

Similar questions apply to the operation of an oven.  Husband tells me – and it makes total sense – that modern ovens use hardly any electricity once they get to temperature.  (Ours displays a light when it is topping up the temp, and this light is hardly ever on!)  I hardly like to mention the difficulties of costing gas consumption – I think I would be happy to tell people that ‘modern, well insulated gas ovens cost less’ once we’ve got a good figure for electricity, and leave it at that.  But what does an oven actually cost to run for 30 minutes?  2 hours?

QUESTION 3.

So what is the real cost?  Obviously I appreciate this will vary.  Even the kWh cost varies, for heaven’s sake.  And the start temperature of the crockpot.  And the efficiency and insulation of the SC.  But I’m sure we can improve on telling people that a slow cooker costs 19p to 49p to use, which is what the site listed above (and others)  is/are  telling people on current prices.

A friend used a plug in power and energy monitor (PEM) on the kWh setting to measure a 6 hour slow cook, and came up with results which suggested that what the PEM was doing was actually taking the max wattage used and multiplying it by the time the PEM was plugged into it.  The same faulty maths, in fact.  Husband (an electrical engineer) tells me that the kWh setting on these simple machines is useless, and common sense would suggest he is (as ever!) right.  Using the wattage setting suggests a far, far lower reading.  When we plugged in our SC the wattage reading was in low single figures initially – the time when the reading would be relatively high, as this is when the pot itself would be heating up.

I do remember that when SC were launched as a major product the advertising blurb was that they cost about the same as a lightbulb.  Even this seems high, frankly.  Lightbulbs of the time were 100w, and lightbulbs DO draw 100w consistently.  SC do not.

The only way I can tell of demonstrating the real cost (without spending lots of money on specialist equipment) is to have a video recording of the PEM the drawdown of watts over many hours, and then averaging this.  Another, much simpler way, might be to ask the SC manufacturers.  Of course, they want to sell SC, so are likely to give optimistic figures.  But I thought this question was worth discussing on here to see if I could get any helpful input.

Thank you for any helpful contributions, which I hope will help some people who are really suffering from rising costs at the moment.

I was a board guide here for many years, but have now resigned. Amicably, but I think it reflects very poorly on MSE that I have not even received an acknowledgement of my resignation! Poor show, MSE.

This signature was changed on 6.4.22. This is an experiment to see if anyone from MSE picks up on this comment.

## Replies

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Another thing to consider, which complicates it further. Most SC cookbooks say to brown any meat first, and also to use boiling water for the stock. So you are preheating what goes into the SC if you follow those recipes, and will have already used some electricity. However, some people throw everything in as is then just cook it for longer, much longer i.e. overnight and seem to get the same results.
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i tend to blitz my hard veg in micro wave before slow cooking for an hour or so only This works well for me as I can hardly wait once i have cooked something delish
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otb666 said:
Surely if the cooker is jammed packed it will work harder than with one or items in it. Also if you then freeze surplus more electric used  Basic physics or Maths I dunno which.  The same thing with boiling kettle and using a flask. You are still boiling same amount.  So at end of day I just use what i need when i need it. Rather than all this over boiling and cooking  for the future.

I think most people who have been talking about boiling water and putting it in a flask have been people who have Economy 7 and therefore are taking advantage of boiling the kettle when the electric is cheaper than when they want to use the flask contents.
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We've had a smart meter installed at the end of March, and I have to report that in a household of 6 adults, with the heating set to 17℃ and on morning & evening (all day at weekends) and lots of cooking from scratch & baking going on, plus two working online from home, we have rarely exceeded my aimed-for dual-fuel budget of £5 a day on weekdays and only go a little over at weekends - and both weekends have been cold.
Presumably your bill came to under £175 for March? Which I agree per person is ok. My March bill of £65 feels a lot but it is only just me feeling the benefit. I don't cook and I have not had the heating on, and by and large it has been freezing.
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