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A convection oven (or fan-assist oven, fan oven) is an oven that has fans to circulate air around food. Conventional ovens, which do not have fans, rely primarily on radiation from the oven walls, and to a lesser extent, on natural convection caused by temperature differences within the oven, to transfer heat to food. In contrast, the fans in convection ovens allow more heat to be transferred via convective heat transfer.  Fans help distribute heat evenly around the food, removing the blanket of cool air that surrounds food in an oven, allowing food to cook more evenly in less time and at a lower temperature than in a conventional oven.
Convection ovens may include radiant heat sources at the top and bottom of the oven, which improves heat transfer and speeds cooking from initial cold start. On the other hand, some ovens have all the heating elements placed in an outside enclosure and hidden from the food. This reduces the effect of radiant heat on the food. (Note, however, that the walls of the oven will also be heated by the circulating hot air; and, though the resulting temperature is much lower than that of a radiant heat source, it is still hot enough to provide some heating of the food by means of radiation from the walls.)
A fan-assist oven will have a reduction in cooking temperature, compared to a conventional oven. This comparison will vary, depending on factors including, for example, how much food is being cooked at once or if airflow is being restricted by using an oversized baking tray. This difference in cooking temperature is offset by the fact that circulating air transfers heat more quickly than still air of the same temperature; in order to transfer the same amount of heat in the same time, then, one must lower the temperature to reduce the rate of heat transfer to compensate.
Another form of a fan-assist oven is the commercial impingement oven. This type of oven is often used to cook pizzas in restaurants. Impingement ovens have a high flow rate of hot air from both above and below the food. The air flow is directed onto food that usually passes through the oven on a conveyor belt. Impingement ovens can achieve a much higher heat transfer than a conventional oven.
- McGee, Harold. On Food and Cooking: The Science and Lore of the Kitchen, revised 2004
- Ojakangas, Beatrice. Cooking with Convection, Everything You Need to Know to Get the Most from Your Convection Oven, 2009.