No oven "requires" preheating. The food you cook in it however does require it if you are baking or you are roasting and want to get a sear on the exterior. Those functions require that the food be exposed to heat from the beginning. Most other recipes can be altered to start with a cold oven. Just add on 15-20 minutes for the oven to come up to temperature onto the cooking time. I often do a roast chicken by starting with a cold oven and it comes out just fine.

Ovens that "don't" call for separate preheating may have a built-in preheat function. The old Martha Washington (yes, that's a brand) wall oven in the house my built in 1964 had an automatic preheat that ran both the bake & broil elements until 350F was reached (if the thermostat was set at least that high).

Thanks. I understand what and why preheat is used, it was just that Jenn Air boasted no need for it (that it is ready the instant you turn the oven on at whatever temp you set). Have not heard this so was curious since I have only seen it in Arch. Digest.