Although the word convection is usually used to describe the natural circulation of gas or liquid caused by temperature differences, the convection in "convection oven" has a more general definition: the transfer of heat via movement of gas or liquid. In a regular oven, convection occurs due to the temperature difference between air near the heating element and the cooler air near the food being warmed. A regular oven relies on a combination of radiation from the walls and, to a lesser extent, air convection to heat the food. Convection ovens impart more convective heat than regular ovens by using fans to force air movement.
By moving fast hot air past the food, convection ovens can operate at a lower temperature than a standard conventional oven and yet cook food more quickly. The air circulation, or convection, tends to eliminate "hot spots" and thus food may bake more evenly.
An impingement pizza oven at a Hungry Howie's store in Auburn, Alabama A convection 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 over sized 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.
Many convection ovens also include a proofing capability using the same fan but at a much lower temperature. A residential double oven will often include the fan capability in only one of the two ovens.
Convection microwave ovens combine a convection oven with a microwave oven to cook food with the speed of a microwave oven and the browning ability of a convection oven.
Another form of a convection 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. Air flow rates can range between 1 and 5 m³/s. Impingement ovens can achieve a much higher heat transfer than a conventional oven.
Like the "impingement oven", a convection oven usually has the radiant elements in view of the food, which improves heat transfer and speeds cooking from initial cold start. Some ovens have the heating elements placed in an outside enclosure and hidden from the food. This eliminates radiant heat from direct contact with the food.