> It's not hard to understand

Please don't patronise!

My oven, on full power, draws 2KW (at least, that's what the labels on my fuze-box suggest). If only 12% of that energy is used to heat the food, then the oven amounts to a 200W food cooker, combined with an 1800W electric heater (I rounded down to 10% to make the reckoning easier).

I live in a studio flat; my oven is in my living room. How come I can survive without A/C? But I seem to be able to roast and bake without my home warming up.

My microwave is an old cheap one, with a max. power of 700W. Assuming that's 100% efficient, then it should cook food about 3.5 times faster than the inefficient oven, I guess; and it does. So it does seem that the oven is inefficient. But why? Where is the lost energy going?

Most of the energy created by the oven doesn't actually go into the food, it heats up the air which heats up your food (and also the walls of the oven). While a microwave pretty much only heats the water molecules in your food.

To roast a chicken to 165f you'll probably set your oven to 400f. And then when it's done, the air and interior of your oven are still very hot. When you microwave food, you can touch the side-walls of your microwave right away and they won't be hot. The only excess heat in a microwave comes from the food steaming and contact with the platter.