A convection oven has a fan and an exhaust system. This is what makes it stand out from regular ovens. An ordinary oven will cook the food by heating the outside of the food with hot air. The outer parts of a dish are continuously exposed to the higher heat and the food is kept in the oven until this heat has reached the inner parts and cooked them.
A convection oven uses a fan to blow around the air more evenly. Not only does it make the air hotter because the force on the air produces more heat, but it also distributes it more evenly.
Convection ovens can produce up to 30 percent more energy. However, this will depend on the power of the fan. So a convection oven cooks your food faster and is hotter, even without preheating!