If you are preheating cast iron in the oven, you want to set your oven to 500 degrees Fahrenheit and place the pan in the oven. Of course, in addition to having patience when you preheat your cast iron, choosing the right burner for this cookware is equally important. You want to match the size of your skillet, pot, or pan with the size of the burner. If you place a large cast-iron skillet on a smaller burner, you are also going to end up with hot spots. It might not seem like a big deal, but uneven heating can damage your cast iron.