What is the difference between a convection and a conventional oven?

A conventional oven heats using elements at the top and bottom and relies on natural air movement. A convection oven, often called a fan oven, adds a fan to circulate air actively. Some designs place a heating element around the fan itself, which is why terminology varies between fan oven and fan-assisted.

The circulation produces three practical differences. Temperature is more even, so results vary less with rack position. Heat transfers faster, so food cooks more quickly at the same setting. And moving air removes surface moisture faster, which promotes browning and crisping.

The standard conversion is to reduce the temperature by around twenty degrees Celsius when using a fan, or to shorten the time. Most recipes state conventional temperatures unless specified, and many ovens print both on the dial. Failing to adjust is the single most common reason food browns outside before cooking through.

The fan is genuinely better for some things and worse for others, which is why ovens offer both. It suits roasting, multiple trays at once, pastry and anything where crisping is desirable. It is less suitable for delicate items that a moving airflow can disturb or dry, notably some cakes, custards and soufflés, and for anything where a moist environment matters, such as bread with a soft crust.

Because air circulates, a fan oven can cook on several racks simultaneously with reasonably consistent results, which a conventional oven cannot.

A related but different thing is a countertop air fryer, which is essentially a small convection oven with a powerful fan and short distances. The cooking mechanism is the same; the speed comes from scale rather than a different principle.