The amount of electricity (and hence the cost) that it takes to cook a meal is the power draw (watts) MULTIPLIED BY the time it takes to cook the meal.
A saucepan has a high power draw for a short time while it is heating up, followed by a moderate power while it is cooking.
A pressure cooker uses less energy because it has a high power draw for a short time while it is heating up, followed by a moderate power for a shorter cooking time.
A slow cooker has a low power draw for a very long time while it is cooking. It could conceivably cost much more to cook a meal in a slow cooker than in a saucepan.
Choice has repeatedly fudged this issue with waffly statements such as that slow cookers “Use less energy than having the oven or cooktop on for the same amount of time.” (https://www.choice.com.au/home-and-living/kitchen/benchtop-cooking/articles/slow-cookers-vs-multicookers-vs-pressure-cookers)
It is possible, but it is likely Choice (@AliceRichard) is correct.
Slow cookers work by a thermostat where heating only occurs when the temperature of the basin containing the food is below the preset level. So, energy used isn’t a simple calculation of time x rated consumption in watts. There will be a factor which needs to be considered for thermostat switching on and off.
A cooktop works differently. There isn’t a thermostat which switches heating on or off. The only regulation is how hot the heating source is. A cooktop will have a energy consumption similar to time x rated consumption in watts. As a cook top element consumption is likely to be more or less than 1500W when the heating element is heated (noting consumption may be higher until the heating source achieves the set temperature). A slow cooker uses a fraction of that of a cooktop.
Even with considering the period of time a cooktop/slow cooker is used, they still are more cost effective to run. Choice isn’t the only one with this view…
But, if you flash cook food quickly on a cooktop, then it is possible that a cooktop may be cheaper to run. Flash cooking isn’t a equivalent a cooking method to a slow cooker, so whether arguing this type of cooking is cheaper isn’t representative for comparison purposes.
The Sydney Morning Herald estimates that a slow cooker is a cheaper way to cook than an oven.
The Centre for Sustainable Energy says, “a slow cooker is a peak demand reduction device” (Less is More in Weston and Easton | Centre for Sustainable Energy), but that addresses only its peak power demand.
But is a slow cooker as cheap as cooking in an ordinary saucepan, and is it as cheap as a cooking in a pressure cooker that produces results similar to those of a slow cooker?
And has anyone actually measured the energy consumed in slow cooking, compared with the energy consumed in conventional stovetop cooking or in pressure cooking?
All the followings links look at the time and cost of cooking and comparing slow cookers vs other ways. Over all the slow cooker comes out the cheapest. While the costs are in OS currency, the energy difference saved is quite marked even for a slow vs a 1 hour oven cook.
The articles that you reference tend to confuse power (kW) and energy (kWh), and to wrongly assume that stovetop cooking always has the burner at full heat. They also provide widely different estimates of the power used by slow cookers - one says, “A slow-cooking pot only uses 0.7kWH – 1.3kWH of energy per hour” (i.e. 700 to 1,300 W) while another says, “slow cooker power consumption in the UK is typically between 100W and 160W.”
Does a Slow Cooker Use a Lot of Electricity? Quick ANSWER implies that a pressure cooker uses less than 10% of the electricity of a slow cooker.
It says, “A pressure cooker or instant pot roughly needs 0.8kWh of energy per hour.” That implies 0.4 kWh for 30 minutes of cooking time (including time to bring the cooker up to pressure.
In contrast, it says, “A slow-cooking pot only uses 0.7kWH – 1.3kWH of energy per hour.” That implies 4.2 to 7.8 kWh for a six hour cooking time.
It also says, “a ceramic electric hob uses 1200 watts to 3000 watts, depending on the size.” With the lid on a saucepan, you can simmer it on much less than 1200 watts. Even if you ran a stovetop burner at maximum heat for an hour, you would use only 1.2 kWh to 3 kWh of electricity.
Are Slow Cookers Energy Efficient? says, “halogen ovens [what Australians call “air fryers”] are typically around the 1200W mark.” An hour of baking in a halogen oven would use about 1.2 kWh. It also says, “slow cooker power consumption in the UK is typically between 100W and 160W.” So 6 hours in a slow cooker would use between 0.6 and 1 kWh.
Most slow cookers use around 75 and 150 watts of electricity on low and between 150 and 210 watts on high. For the whole of the cooking cycle (such as starting on high and then low to finish the cooking cycle, a slow cooker will use around 700W or possibly more if the high setting is used for the whole of the time it is on. What you say here is correct…
and the upper usage would be based on high setting being used longer in the cooking cycle.
Choice and other reputable sources compare slow cooked foods in an oven or cooktop with that prepared in a slow cooker. Slow cooked foods such as a tender/pull type roast or a soup where the meat falls apart. As outlined above, it isn’t comparing fast cooked foods with slow cooked foods. Using this comparison isn’t comparing apples with apples.
An example of equivalent recipes would be cooking a roast in a slow cooker for 8 hours. In a slow cooker that is rated to 75 up to 210 watts (total usage of around 0.7W to 1.3kW) this would compare to a slow cooked roast in the oven for 3 hours where the oven at low temperature would use around 1500 watts (total usage if around 2 to 3kW).
Likewise with cooktops, slow cooking on a cooktop takes about 2-4 hours on low. The energy usage of a cooktop is many multiples of a slow cooker (your example of a ceramic cooktop looks about right being around 1200 watts). The ceramic cooktop uses about 10 times the energy of a slow cooker which shows that slow cooking on a ceramic cooktop will use significantly more energy than a slow cooker.
When equivalent recipes are cooked in a slow cooker, it is far cheaper and uses less electricity than in a oven or on a cooktop
To do the job accurately I would skip all these calculations (and miscalculations) that draw conclusions about the energy used to cook something and instead measure the energy actually used while doing the job as described.
This measurement does not seem to be have been done by any of the reports. So rather than compare reports that use the computation method, some of which are hard to follow if not wrong, my answer is we don’t know for sure.
Slow cookers and other devices do not do well on all kinds of cooking so their outcomes are not comparable in some cases. Unless the outcome is set to something ovens, stoves and slow cookers can all do (like a stew) energy measurement is not very useful.
To me the outcome and the convenience are more important than the small difference in cost of running. I am going to pick the equipment based on what I want for dinner not the energy cost as the difference in cost will be swallowed by the difference in cost of ingredients. You will make your saving by choosing blade instead of fillet not the pot you cook it in.
The dispute about the claim that “A slow-cooking pot only uses 0.7kWH – 1.3kWH of energy per hour” (i.e. 700 to 1,300 watts) indicates that there is significant misinformation on this topic. The label on my large Ronson slow cooker says 255 to 280 watts. So in 6 hours it could not use more than 1.7 kWh.
I accept that a slow cooker uses less electricity than an oven, for the same result.
I am yet to see an article that clearly demonstrates that a slow cooker needs less electricity than a pressure cooker, or even a stovetop saucepan - to produce a meal “such as a tender/pull type roast or a soup where the meat falls apart.”
Let us take this as a given.
We are as one it seems.
Where we may disagree however is; does it actually matter?
It matters to people like me who want to minimise their energy bills, to people like me who want to minimise their greenhouse emissions, and to pedants like me who abhor misinformation 
Part of the equation not mentioned is the food and possibly the convenience. Is the product of a slow cooker the same as one made on a cooktop or in an oven? Unless the food and recipe and outcome are the same the power consumed seems a side issue unless the weekly menu is made based on power consumption for cooking.
I doesn’t use it per hour. The number will be the likely total energy consumption when using a slow cooker, not the rate of use. The authors in the article appear to have made an error in relation to the units used.
Yes, it is possible if you cook a meal on high and the thermostat to maintain constant temperature was faulty causing the slow cooker to operate at maximum power for the whole time the slow cooker was on, the cooker could reasonably be expected to use up to 1.7kWh. If the slow cooker worked correctly (wasn’t faulty) and one follows the user guide in relation to using settings 1, 2 and automatic - the amount of energy used would be significantly less that that. The ratings on an appliance are the maximum draw/power consumption not the average usage when operational.
For a
these usually take 3-4 hours to cook on a cooktop. Smaller roasts will take short time, bigger roasts longer.
A soup with tender meat takes between 2-3 hours (again depending on the side of the meat). This is an example recipe:
As indicated in an earlier post, using a cooktop for 2-3 or 3-4 hours for meals which one could readily cook in a slow cooker will use significantly more energy and cost more. For a cook top heating element that uses 1000-1200W, total energy use would be in the order of 2-4kWh compared to around 0.7kWh for a slow cooker.
It is also worth noting that the comment in the Choice article was:
- Use less energy than having the oven or cooktop on for the same amount of time.
which is correct as the power consumption of a slow cooker is considerably less than for an oven or cooktop. Choice is possibly incorrect as meals cooked on a cooktop/own are likely to take half the time of a slow cooker, which means the comment isn’t realistic in a practical sense. Choice could equally (and possibly more correctly) have said that it uses less energy for similar recipes than those cooked in an oven or on a cooktop.
The Huntington Waterfalls article concludes that “Cooking for 8 hours a slow cooker uses a similar amount of power that a stovetop uses in just 45 minutes,” but is seems to mistakenly assume that both the slow cooker and the hotplate operate at maximum power for the entire cooking time.
A soup with tender meat takes about 30 minutes in a pressure cooker. I find it hard to believe that cooking in a pressure cooker would use as much energy as cooking in a slow cooker.
There appear to be some inconsistencies in the use of units in the preceding posts. It may reduce some of the misunderstanding if we can recheck and if necessary edit or clarify whether the comments are with respect to total energy consumed or the rate of delivery of the energy (power).
Electrical energy used is usually measured in kWh which is also the basis of billing. Although Joules (J or kJ etc) is the more universal SI way to measure energy. Power is measured in Watts (W or kW etc).
In operation of the electrical cooking devices, ovens, cooktops, etc the temperature or power setting is usually supported by a thermostat. There are various comments that it would be more useful in any comparison to directly measure the energy used. A better alternative than to guess at the duty cycle and power controller characteristics, which is not so scientific.
Note:
It’s very evident from our smart meter consumption data when we have been using the microwave or air frier for cooking. The slow cooker impact is less evident, but for longer.
You are correct that a pressure cooker on a cook top will cook quicker than an open saucepan. We find that it takes about third to half the length of time as in a recipe and once pressurised, the cook top can be turned down to maintain the temperature and pressure.
I can’t information on whether a pressure cooker (plug in or stove top) has a higher, lower or similar energy usage as a slow cooker. My own gut feeling is that it would be similar or more, but unless one does it is a controlled way and cook a range of recipes with the same end result, it won’t be able to be substantiated.
In relation to plug in type pressure cookers, Choice doesn’t comment on whether they use more or less energy than a slow cooker, oven or cook top. It is also worth noting that it is likely that most purchased today are pressure cookers which plug in rather than the older cook top models, as the plug in models tend to dominate the retail market.
I believe you have picked up on a misprint. They offer several times that the energy used in one is around 0.7 kWh to 1.3 kWh for an 8 hour cook. The one instance of the hour comment links to further details that explain that “Most of the slow cookers in the UK use 1.3kWh in six to eight hours”.
It is easy to determine that it is a misprint in that a 160 Watt (0.16 kW) device in an hour cannot produce energy usage of even 0.7 kWh of energy. It would use 0.16 kWh of usage over that hour, 8 hours this would be 8 X 0.16 kWh = 1.28 kWh. The low power setting would be less than this figure, high power at 240 Watts (0.24kW) over 8 hours would use 1.92 kWh of power or roughly $0.50 of power.
I would expect a slow cooker to use less energy than a conventional oven, but figuring out if they’re more efficient than an air fryer, pressure cooker, or covered saucepan would require some testing.
An oven is larger, with more thermal mass (the steel racks, inner steel body), and operates at a higher temperature of about 180°C. One model of 60cm oven has a listed weight of 33kg. Let’s assume 10kg of that is the the inner steel body.
Slow cookers operate more around 85°C. One 6 litre model weighs 6.1kg. Let’s assume 2kg of that is inner steel.
It takes 0.466 joules of heat energy to raise the temperature of 1 gram of steel by 1°C. Room temperature is conventionally 20°C.
So the slow cooker needs to heat its steel interior by 65°C, using 60 kJ to do so. The oven uses 596 kJ.
(the extra air inside an oven makes a difference too, but it’s pretty minimal. Each litre of air costs 1.2 joules to heat by 1°C (assuming typical humidity). So an empty slow cooker spends 0.47 kJ heating 6L of air, while the oven, with a listed capacity of 72L, spends 14 kJ)
Of course, this assumes perfect insulation. As heat is lost to the environment, the thermostat will intermittently turn on the heating element again. But since heat loss is proportional to the temperature difference, and to surface area, a slow cooker would have to be really badly insulated to perform worse than an oven, even given the longer cooking time.
There’s lots of other factors to consider too, and obviously a back-of-the-envelope calculation is no substitute for actual rigorous testing. But when the calculations suggest an oven uses roughly 10× the energy, that’s a big hurdle to overcome.
Perhaps you could have done some research.
The below Choice article discusses running costs for various cooking methods. Whilst an individual’s usage pattern may differ from that mentioned in the article, an estimate of your annual costs can be easily worked out.
Given that the cooking costs for the methods you have listed are likely to be a small component of the total meal cost, most people are likely to choose the method that gives them the best food outcome.
The July 2022 Choice article is much more informative. It indicates that pressure cookers use the least energy, and that slow cookers use the most.
It says that multi-cookers (which include a pressure cooking function) “use less energy than having the oven or cooktop on for the same amount of time.”
A pressure cooker requires much less cooking time than an oven or saucepan, and so uses much less energy.
It also says that a slow cooker’s “running costs are on par with, or slightly more than, using an oven.”
It provides the following running cost estimates:
Air fryer: $9 to $51 for 78 hours of cooking.
Cooktop: $32 to $56 for 78 hours of cooking
Oven: $31 to $56 for 156 hours of cooking
Slow cooker: $23 to $98 for 1,251 hours of cooking.
It is worth noting that the running costs aren’t comparing like for like meals, but what is considered average running times of the appliances within a household. This is recognised in Choice article by:
Although it’s difficult to compare the same cooking tasks like for like (due to the different methods and styles of cooking for different appliances, plus the fact that same types of cooking appliances vary in efficiency), we’ve laid out the average running costs for each cooking appliance to help you understand any changes and cost savings you could make.
Not quite.
While the cost estimates are relevant to the likely running costs in an average household, it unfortunately doesn’t satisfy the question of what is cheaper or more efficient way of cooking the same meal in difference appliance. Such an answer would provide information on what is the most efficient appliance for different meal types.
Choice touches on like for like meals, without providing any quantification, by the statement…
“Smaller appliances generally use less power than larger ones, so using the microwave instead of the oven and the toaster instead of the grill, for example, will save you money. An air fryer may not be suitable for all cooking tasks, but will use less energy than an oven as it is smaller and quicker to heat up and cook smaller quantities of food.”
One could roughly extrapolate like for like meals, for example, a slow cooker meal taking 8 hours costs $23 to $98. The same meal on a cooktop would take say 3-4 hours with annualised cost of roughly $192 to $336. This gives an indication if why choice made the above statement and shows slow cookers for like for like meals would be significantly cheaper in relation to overall energy costs.
