Fan oven or conventional? How to convert oven temperatures

With conventional heat, elements at the top and bottom heat the oven while the air stays still. In a fan oven, called a convection oven in the US, a fan moves the hot air around, so the heat reaches the food faster. That is why you set a fan oven about 20 °C lower than conventional heat and keep the time the same.

The same works the other way round: if a recipe gives a fan temperature and you bake with conventional heat, add 20 °C.

An air fryer is essentially a small, powerful fan oven. The hot air has only a short way to go and moves fast, so it cooks even quicker. As a rule, set it 20 °C below a fan oven, so 40 °C below conventional, and expect about a fifth less time.

An example: a bake that needs 30 minutes at 200 °C conventional cooks in the air fryer at 160 °C in about 24 minutes. Many air fryers only go up to 200 °C, so for very hot recipes the oven can be the better choice.

Frozen food follows its own rule, and many packages now print it: about 20 °C less than in the oven and just under two thirds of the time. Fries that take 16 to 17 minutes at 220 °C in the oven are done in the air fryer at 200 °C after a little over 10 minutes. Shake the basket once halfway, so everything browns evenly.

Every oven heats a little differently, and the dial doesn't always match the temperature inside. So the first time, check about five minutes early, especially with cakes and pastries.

To convert Celsius to Fahrenheit, multiply by 9/5 and add 32: 180 °C is 356 °F and 200 °C is 392 °F. The other way round, subtract 32 and multiply by 5/9: 350 °F is just under 180 °C.