They are different, not only in size, but also in how they cook. While different ovens can cook in slightly different ways, the general idea is to get them to a particular temperature, and then let the food cook at that temperature. But the hot air is relatively stagnant. An air fryer, heats up as well, but it forces the air to move quickly around the food, cooking it in half the time, and often giving the food a crispy outside texture. Air fryers work more like a convection oven. So the movement of the hot air is really what cooks the food.