Hi Steve, as has already been mentioned, a convection oven is simply a normal oven with a fan in it. It allows you to cook using a lower temperature setting, and cook faster. It is the reason why which is interesting.
I should probably introduce the concept of dry and wet bulb temperatures. If you place a thermometer in an oven, and it registers (say) 150C (302F), that is the dry bulb temperature. The setting that you have on your oven only controls the dry bulb temperature. However, if you wrap the bulb of the thermometer in wet cloth and put that in the oven, it will register a different temperature. The temperature of the water in the cloth can never exceed its boiling point of 100C (212F), so it will register a much lower temperature. This is the so-called "wet bulb" temperature, and is effectively what temperature your food is exposed to, and is cooking at. Your food will NEVER exceed 100C/212F until all the water is driven off, but I don't recommend cooking food that long
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One thing to note though: the wet bulb temperature will be different if you turn the fan on, as opposed to fan off.
The reason why - a roast in the oven will have a layer of cooler air around it called the boundary layer. This air is cooler because it is cooled by evaporation from the roast. This effectively insulates the roast from heat. The fan removes the boundary layer and increases the wet bulb temperature. This is why food cooks faster in a convection oven.
Incidentally, it is possible to calculate the humidity of the oven if you know the difference between dry and wet bulb temperatures. This is how Kombi ovens (with an adjustable humidity control) work.
As for what time setting to use ... don't use a time setting. Get yourself a probe thermometer like a
Maverick ET-732 and cook to temperature. As for what temp setting to use, you should think of the "delta-T" - the temperature gradient between food and oven. A low delta-T (i.e. lower temp setting on the oven) takes longer to cook your food, but will give you a larger window of opportunity to remove your food before it overcooks. The downside is that a low delta-T does not provide much browning, and is more likely to dehydrate your food if you are cooking something thin.