Fan oven temperatures I have had installed two new Neff top of the range ovens. My question is : if you cook cakes in a fan oven at 20 degrees less than you would in a conventional oven ie 170 instead of 190 (as instructed in recipes) does the temperature in the oven rise to 190 even though you have it set 170 fan? 
Thank you
Anne Edgley
No, the temperature remains at 170C, fan ovens heat faster because the air is kept moving. It's the opposite to wind chill, where it feels colder because the wind is blowing more cold air molecules over you than if it was calm. In an oven the fan is blowing hot air over the food, making more hot air molecules touching the food per second than without the fan.