Convection ovens use a fan built into the back of the oven to circulate warm air around the food during cooking. This feature allows for even heating and better browning of foods. Additionally, foods cook at a lower temperature and over a shorter duration of time compared to conventional ovens.
Convection ovens have been used in professional kitchens since the 1950s and have found their way into the home as either stand-alone countertop ovens or as a setting option on ovens purchased over the last 20 years.
Conventional ovens radiate heat from either a top or bottom heating element. This can result in an oven with hot and cold spots, as identified with an oven thermometer. With a conventional oven, items may not cook or brown as evenly due to temperature fluctuations. Food may need to be rotated to compensate. Convection ovens don't have these hot and cold spots because the internal fan keeps the warm air moving.
For best results with a convection oven, baking dishes should be shallow and have a two-inch clearance around their sides. This allows for even air flow around the food. For the same reason, items made in a convection oven shouldn't be covered with aluminum foil.
Due to the efficiency of convection ovens, the cooking temperature can usually be reduced by 25 degrees and total cooking time reduced by about 25 percent.