But nowhere near as efficiently as a dedicated electric heater, because the oven doesn't actually push air into the other room. Instead, it has to operate at a higher temperature, in order to create the temperature gradient down which heat conducts. That's vastly less efficient than having a heater with a fan. See my first example in reply to GB.
If you have a computer which keeps all the heat inside it, then you're going to have overheating problems...
This is already established by overwhelming scientific consensus.
Yes - allowing for the points that this only applies when you'd want the heating on, and also acknowledging the difference between gas and electric, if you have gas.
You think that the basic laws of physics don't apply to toasters?
I already said that a computer's fan moves air from inside the case to outside the case.
What I've been saying is that the amount of useful work done by a heater+fan combination is not simply the total amount of heat pumped out, but also in pushing the air around the room to facilitate convection. The heater+fan clearly does more useful work than just the heating element by itself, and not because the fan also produces heat, but because it facilitates convection. I've also looked at it from the other way: a heater that just heats one single molecule and doesn't let that molecule go anywhere is not doing any useful work, even though it outputs a great deal of heat. And, most recently, I've looked at it from a third way: if you need a 1,000w heating element to create a sufficient temperature gradient to heat a room (i.e. replace heat lost from windows/doors after at equilibrium, which in a previous example escaped at a rate of a), but you only need a 500w heating element and a 100w fan to heat the same room, then the fan has done more useful work than the extra 500w pumped out by the first heater.
Heh, now who's switching arguments. I'm not saying it doesn't reduce the heating required, because that would amount to saying that it doesn't produce any heat at all. What I'm saying is that they're not as efficient as electric fan heaters (or, put another way, that an electric fan heater drawing the same amount of power would reduce heating required more). If you operate under the naive belief that any heat out is useful heat, or the rather baffling belief that there's no utility in forced convection, then of course you will find that all electrical devices are as efficient as each other. But efficiency is about useful output, not just heat that lingers around the ceiling or at the back of a fridge or around a toaster.
Which then heats up the room as well as any radiator.
Do you at least concede that a computer is just as useful as a radiator of equal power - even if you're arguing that a fan powered heater of equal power is better?
How does it not let the molecule go anywhere? Heat rises. The heat out of a computer (or by a radiator) spreads through the room by convection.
So you agree that electric fans are no better than a computer, as neither's fans are to do with spreading heat around?
I'm not sure I've ever argued only using your computer to heat the house.
Which is wrong, by the basic laws of physics. Possibly you mean something other than efficiency, but I'm still not sure what you mean. A fan heater is good if you've just come in from the cold and you need something to heat you up really quick - but that's irrelevant anyway, when it comes to the normal way in which people heat their homes. I want my whole house to be warm, and any heat added to that by a computer is done so with 100% efficiency. My computer isn't on when I've just come into the house - but it's on during the hours when I've also got radiators on, maintaining a warm temperature throughout the house.
You have your computer stuck on a ceiling? If so, I guess that explains why your computer isn't as good as heating the room
Most people have them on floor level.My computer is next to the window, and my radiators aren't - so my computer is more efficient then?
Of course it has, as that's how most people heat their homes. Even for electric heaters, it's only the smaller ones that tend to have fans, not all of them do. Is all of the heating in your home fan powered?
How?
If your radiator is under the window, it doesn't have to create as large a temperature gradient in order to replace heat lost at the window as a radiator placed at the other end of the room, say. The reason is just that the cold air from the window falls and the hot air from the radiator rises; if the radiator is on the opposite wall, the hot air will just sit at the top of the room, like a lightbulb, before being pushed to the window and cooled, meaning that you'd have to have a much hotter radiator in order to heat the room. I'm much less confident about the actual temp required for a radiator under a window, though; I can't remember what reason I had for saying "just over room temp" specifically, since I suppose it depends on the strength of the convection current created by the window. The point, though, is that the heat from the radiator rising counteracts the cold air at the window falling, meaning you get a "virtuous" convection cycle, rather than the vicious one that happens with a radiator at the other end of the room. I was probably overzealous saying it was "MUCH" more efficient than other options; it might not be, since a fan might be better than the "natural" current created by the window at reducing the radiator temp required.
Even if this does make a difference, as I say it's irrelevant to the computer versus radiator discussion, since you can have radiators that aren't under windows, and computers that are.
Yes, if you spend all your time sat in one location of your house, it's cheaper to just blast hot air at you rather than using a non-fan radiator or computer. But it's still true that a computer is no less efficient that a non-fan radiator.
The position matters only in the sense that most people don't live on their ceilings. And since heat rises, a heater stuck at the ceiling might be a problem, because some heat will immediately be lost. The point is it doesn't matter if having a heater on the ceiling is less useful - if it's true, then it's irrelevant because computers aren't stuck on the ceiling. If it's not true, then the argument is irrelevant anyway.
) doesn't get made up or destroyed out of nowhere. 
As I said, the natural convection current in the room may or may not mean that a fan is unnecessary. See above for how the placement of the radiator is important in exploiting the natural convection currents created by the radiator and window, and conversely how bad radiator placement creates a vicious circle where a room never gets heated properly.
I know it has a specific meaning in thermodynamics, but I can't think of a better way of describing, say, "heat that just lingers in places you don't want to heat" using common English words. The key word is "useful", which is why I bolded it, rather than "work".
Yeah, there's no such thing as perfect isolation, but as you said, it was a thought experiment. It's a reductio ad absurdum of heat that lingers at the ceiling or inside a toaster. The point is, heat that doesn't actually get to the place where you want it (e.g. person-level in a room) isn't useful.
Yes, you're right, I shouldn't have mentioned equilibrium at all. What I meant by that was just that the person-level temperature was at the required level to begin with, so ignoring how long it takes to heat the room up, not that the whole room was actually in thermodynamic equilibrium. In fact, what I'm saying kinda rests on the room not necessarily being in thermodynamic equilibrium during the time in which the heating is actually on, so using the word "equilibrium" was even more misleading...
"Efficiency" just means "useful output" / "useful input". It doesn't matter whether the context is engineering or economics, it's all the same. I studied neither engineering nor economics, but the principle is the same: if some heat produced isn't actually doing something useful, it can't go on the numerator of that equation.It's not a naive belief, it's reality. It's the first law of thermodynamics. Energy (unlike money
And, continuing with the comparison to money, in thermodynamics (unlike economics) "efficiency" is not a magic word which can be used to justify that creation or destruction of energy out of nowhere. It shouldn't be abused in economics either, but that's not a science so they get away with anything.
