Never quite understood why ovens with fans are called convection ovens. Whether it has a fan or not, heating air to cook food is convection cooking. I'll just call it forced air cooking. Forcing air flow is a way to distribute the heat more uniformly. In a typical fan-less oven the temperature sensor (usually a thermocouple) is located at one point and that happens to be away from the food. You may have the temperature set to 350° F, but when empty there will be at least a 50° variation. Add a 10x10x2 cake and the temperature differential will be over 125°. Add some airflow and that temperature differential is reduced. Most residential ovens will still vary by about 75° F. For a little extra credit, when you move the air fast enough to penetrate the boundary layer of air that hugs the top of any surface its considered impingement. Impingement can easily cut the baking time in half over the typical forced air oven, but enough about that. As a result of more uniform air temperature food will cook faster, but that's not always a good thing. So for the residential user the alternative is to reduce temperature. Another thing to consider is what happens when you bake something from batter. Where does the heat really go? Generally about 75% of the heat goes to evaporate the water, and less then 25% actually heats the cake. As the water is evaporating, the air above the center is cooled, or in terms of an oven is "chilled". Meanwhile the air also transfers heat to the container which conducts heat to the batter. That conduction inputs far more heat to the food then the air does. Its all about understanding some of the simple physics of what's going on when food cooks, and from there you'll be better able to predict how to cook with a "convection" oven.

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