In Facebook groups I see many people using a sous vide stick in a pot or in a container without a cover or insulation. This made me wonder how much difference it actually makes for your electricity bill and your carbon footprint. And so I decided to do an experiment.
For this experiment I heated up 8 litres (8.5 quarts) of water with a sous vide stick to 74C/165F and then switched off the heating but continued the circulation, by setting the target temperature to a very low value. After an hour I noted the temperature that the water had cooled off to in that hour. This is a good indication of how much power would have been needed to keep the water at 74C/165F during that hour.
With a polycarbonate container without cover or insulation, after an hour the water had cooled off to 48.7C/119.7F. Because water has a heat capacity of 4186 joules per litre per degree centigrade, we can calculate that .24 kWh of heat was lost during that hour. (So if you cook something for 24 hours at 74C/165F, in a container without cover or insulation, approximately 6 kWh of power will be lost and need to be added back to the water by the sous vide stick to keep the water at the right temperature.)
Furthermore, from the original 8 litres of water…
…about 1/4 litre (1 cup) of water had evaporated. So for longer cooks the water level will become too low, and the sous vide stick will stop.
Then I repeated the experiment with a cover. Now the temperature dropped quite a bit less, so 34% of the heat loss was prevented by adding the cover.
The water level also stayed at 8 litres, as most of the water that evaporated condensed against the cover and then dripped back into the container. So a cover does not only prevent heat loss, it will also ensure that you can do long cooks without having to check the water level.
Next I added a neoprene sleeve to insulate the container.
The insulation and cover together reduced the heat loss to 51%.
Putting a layer of neoprene on the cover caused a further improvement to 62%.
As a final step I added sous vide balls, that float on top of the water. This produced a minor additional improvement to 66%. So two thirds of the heat loss, and therefore the power usage of sous vide cooking, can be prevented by adding a cover and insulation.
As a reference I also tried the sous vide balls by themselves, without a cover and insulation. The result of this was slightly better than the lid only, but close.
Personally I don’t like to use the sous vide balls, because when you empty the container they tend to bounce all over the place. And as you can see from the results of my experiments, they do not add significant value if you already use a cover.
I also tried a sous vide stick in an 8 litre stainless steel pot. The heat loss was 15% smaller than the polycarbonate container. This can be explained because on the one hand the stainless steel pot has a surface area that is 32% smaller than that of the polycarbonate container. On the other hand, the polycarbonate container insulates better than the stainless steel.
Finally I also tried my SousVide Supreme, which has insulation and a cover. The result was very similar to that of the fully insulated polycarbonate container.
I monitored the ambient temperature and relative humidity during all of the experiments, which stayed constant at 18C/64F and 55%.
This table shows the results of all the experiments. If you care about your electricity bill and/or your carbon footprint, you should at least use a cover, but it also pays off to invest in insulation. A cover and insulation together can save about two thirds of the energy needed for sous vide cooking. For the cooking result you will not notice any difference — unless you ruin the cook because the stick stops halfway through due to too much evaporation.
Stefan's Gourmet Blog 
Interesting experiment.
I use an 11″ circular neoprene cover notched for the machine when I sous vide in a stainless steel pot, and I fashion one out of aluminum foil when I use a brining container. I’ve never bothered to insulate the body of either. I could likely find an insulated quilt or other suitable material I could fashion a wrap out of that would fold up for easy storage. My motivation to reduce wear on the machine would be equal to my desire to conserve energy.
That difference in the stainless steel container might to some extent be because (I assume) the s.s. retains more heat than the polycarbonate. Of course, it takes more energy to fully heat the s.s. up in the first place.
Love your blog. I’ve really enjoyed this method of cooking. I did a “locally raised” sirloin for New Year’s Eve dinner. And I now have a hard time eating chicken breast cooked any way other…just so tender, moist & flavorful when done “low & slow.”
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Hi Bill, that’s a good point about the heat retention in the stainless steel. I am not certain though which effect is stronger: the higher heat retention or the higher heat conduction to the surrounding air.
Thanks for stopping by and taking the time to comment!
Stefan
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Since I got my sous vide six years ago I’ve always loved your experiments. The amount of time and diligence you put into making empirical research is admirable, to say the least. You made the start of using sous vide easier for me, as there at the time wasn’t a whole lot of articles about it back then, and I’ve always been very grateful.
So now that I see that you’ve touched a subject that I’m a bit familiar with myself (but by no means an expert), being a mechanical engineer, I can’t but ask how you came to your conclusions on the energy matter? As I see it, your heat flow will be even bigger than what you calculated in the first instance, since the rate of heat flow is proportional to the difference in temperature between your water and the surroundings.
In short, the heat flow is bigger at 74 degrees than that of 48.7 degrees. So, when you start the experiment you might emit something like 0.5 kW and in the end only 0.1 kW, averaging at 0.24 kW. This only adds to your conclusion that insulation is critical, mind you! It is, however, a complicated matter and is easily avoided if you buy a power consumption meter (here in Denmark they are something like 20€).
I did a very, very simple and unreliable experiment myself once. I measured the time between the clicks of the relay switching the heater on and off and estimated my Steba sous vide to consume around 50 W at 55 degrees, if I remember correctly.
Anyway, thanks again for this wonderful blog!
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Hi Mikkel, thanks for your nice message. I did realize the second order effect you mention, but decided to leave it out of the article to keep it simple (I will edit the text a bit though to make clear the calculation is simplified). As you said, it doesn’t change the conclusion. I didn’t use a power consumption meter because I didn’t want to buy one just for this, and because I wanted to focus on the good of insulation rather than the bad of the power consumption of sous vide cooking. Great to hear you like my blog!
Stefan
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Saving the planet 1 sous vide at a time.
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About 2 years ago, I custom built a water bath that can accommodate 120 bags of protein. During the second trial loaded with chicken breasts, the electricity supply was interrupted. That was just after the halfway mark of the cooking period. During the rest of the cooking period, the temperature dropped just over 1 degree Celcius.
This was only possible due to the superb insulation of the water bath that was completed insulated with the ceramic fibre of 25 mm, and finally with a cosmetic layer of neoprene and this setup allowed the temperature to remain very stable for almost one hour to the end of the cycle.
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That is a thorough experiment, one that JT would love. Happy New Year!
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Where did you source the neoprene sleeve from?
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https://www.sousvidekenner.nl/sv/sous-vide-waterbakken/energiebesparing/kenners-isolerende-hoes-voor-12-liter-waterbak/
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