I'm currently sitting in a very cold room, it's cold because heating costs too much darn money (we haven't got central heating:(). Well, this got me thinking over cheap ways to heat a room. The idea of heating air with microwaves struck me being really cheap and effiecient. But it's so obvious, I thought, that it should be common place. Why isn't it? Is there a reason why the technology of microwave ovens can't be turned to heating nitrogen in air, or water in central heating pipes, immersion heaters, or a kettle even? (and yes, I know about the superheating problem, but this seems easy enough to overcome) The only applications I've seen on the net are industrial, but how easy would it be to scale these processes down? I'm left thinking that it's possible, but maybe copyrights are getting in the way of it being used.