In order to understand convection ovens, there are a few principles you need to understand first:
1) Ovens don’t make things hot. They add heat to whatever you put into them.
2) Heat will always flow from something of a higher temperature to something of a lower temperature. The farther apart the temperatures are, the faster the heat flow.
3) Heat will continue to flow from one object to another until the temperatures of the two objects are equal.
4) Air is really a poor conductor of heat. It is actually a pretty good insulator.
Lets talk about chill factor for a minute. Chill factor? Isn’t that weather stuff? In an oven manual? Yeah, because the concepts are the same. Stick with me here.
If the weather outside is freezing, this may sound funny, but it does not make you cold. What it does is to remove heat from your body, and heat flowing from your body into the air around you is what makes you feel cold.
If the wind is not blowing, your body transfers heat to the cold air around it. The temperature of the air closest to your skin starts to rise. Soon you have a little “blanket” of relatively warm air around you. As the air temperature of this “blanket” rises, the heat flow from your body slows down. When the heat flow slows down, you don’t feel as cold.
If the wind is blowing, the air touching your skin does not have a chance to warm. The wind is constantly blowing away the warm layer of air and replacing it with cold air. The heat flow does not slow down, and you feel colder, even though the outside air temperature is the same as before. We humans refer to this as the chill factor.
The same thing happens inside an oven. If the air is still, the heat does not flow from the air to the food as fast, and cooking is slower. If the air is moving, heat gets transferred faster and cooking occurs faster.
All ovens have some air moving around inside, due to natural convection (warm air rises, cooler air falls.) In a convection oven, a fan is used to force the air to move around inside the oven, speeding up the cooking process.
The fan also has two other functions in the oven. Oven temperatures are pretty extreme conditions in which to operate an electric motor. If the oven is also self-cleaning the temperatures are even higher. So the fan motor actually draws air at room-temperature over itself to keep itself cool.
In a gas oven, air is also needed for combustion. The fan pushes air through the burner. In this system there will also be something called a “sail” switch. This is a switch with a little metal “sail” that activates it. Air from the fan closes the switch contacts when the fan is operating. The sail switch is wired in series with the heating system of a convection oven. If the blower fan is not operating, it is not cooling itself, so you do not want the heating system on. In addition, in a gas convection oven, proper combustion will not occur without proper airflow.