Almost every recipe that uses an oven instructs you to heat the oven ahead of time. But how long does it take to heat? We’ve always allowed at least 20 to 30 minutes for an oven to get good and hot. So we were a bit surprised when our new electronically controlled ovens were beeping to indicate they were done heating in as little as 10 minutes. Could that be true? The answer is “not quite,” and here’s why:

When you turn on an oven, say to 350ºF, the oven doesn’t just shoot up to 350° and stay there. It’s impossible, because oven heating elements are either on or off, and they can’t really maintain a constant temperature. Instead, oven thermostats are designed to strive for an average temperature (the one you set). When the oven is first turned on and starts aiming for the target temperature, it actually exceeds that temperature by as much as 50° to 75°F before the heating element shuts off. The temperature then drops well below the target before the heat kicks in again. In subsequent heating cycles, the range around the target temperature becomes smaller, about 25°F on either side.

Our ovens claim to be heated after the first temperature cycle, but we always ignore the beep and let them go for at least 20 minutes (or about three cycles), before we bake. The extra time means that all parts of the oven, not just the area around the sensor, are fully heated, and that the temperature swings within the oven cavity aren’t as drastic.