The Physics of....Saving Energy with an Air-fryer

I was very resistant to the idea of air-fryers when I first heard of them. I thought they were a fad and that we would one day look back at them like soda streams from the 1970s and wonder why we ever thought we needed such a thing.

And I also thought that frying is something you do with oil, and pretending to do it with air wasn't going to fool anybody for long.

But now I think differently!

If they'd only marketed them as 'small ovens' to begin with, I wouldn't have taken so long to come around to the idea. Because that is all they are - but I have come to realise that small ovens are a very, very good idea. And because I have a lot of important end-of-year things to be done, I put them all aside to look at the maths of this instead,...

My air fryer has internal dimensions of (19 x 19 x 10) cm. And when I do the maths (remembering to convert to metres early in the process like a well-drilled Leaving Cert student), I find that that creates a volume of 0.00361 square metres. And completing the maths as shown here, that means that it takes just over 650 J to heat the internal space to 170 degrees, which is hot enough to cook most things pretty quickly.

And if we do the same maths for the (much larger) conventional oven in my kitchen, we see that to heat that up to the same temperature requires over 12,000 J.

That's nearly 19 times more energy! Looking at it another way, the use of an air-fryer saves 95 % of the energy we use to cook the same meal with a conventional oven!!! That's a pretty extraordinary saving.

It only applies if you don't need all the space in the big oven for your meal, but for my family, we only need that space on Christmas day, and the odd time we do a big roast dinner. You certainly don't need it to cook a few chicken goujons.

And of course because its smaller, it's also much, much quicker. which presumably creates an even bigger saving.

But I still don't know why they're called air-fryers when they're just small ovens!