It comes down to how the heat is distributed. Both convection and conventional ovens are powered by gas or electricity. But the heat source in a conventional oven is stationary, usually radiating from the bottom, while in a convection oven a fan circulates the hot air around the chamber.
Convection ovens allow for even, fast cooking because the temperature stays more consistent, whereas conventional ovens can have pockets of warmer or colder air. Hot air rises, so when cooking food on both racks, dishes on the bottom rack may undercook while the food on top burns, explains Allison Eckelkamp, media representative at General Electric.