Yep, that’s the argument I was referring to. If both heaters have 1500 watts of heating coil, but the forced air heater also has a 10 watt fan motor, both heaters will be rated at a 1500 watt heating capacity, but the forced air model actually consumes 10 watts more. In advertising speak, that’s less efficient.
To the OP, as has been pointed out, electric heat is pretty much 100% efficient, meaning you get exactly as many watts out as heat as you put in as electricity. The only inefficiencies would be in the form of extraneous loads like fans. Now the fan does produce heat as a byproduct of the motor inefficiency. You could also argue that the energy imparted to the air by the fan blades is eventually converted to heat as well, but you’d be hard-pressed to measure it.
I guess the question here comes down to “Does an electric fan motor consuming 500 watts put out 500 watts of heat?” Hopefully someone will come along that knows the answer to that with more certainty than myself, which sets the bar fairly low.
I’m not an expert on thermodynamics, but I think this is true with just about anything you plug into your outlet.
Take your computer & monitor, for example. Let’s say you measure the real power it consumes at the 120 VAC outlet, and it’s 300 watts. Does this mean your computer & monitor pumps 300 joules of energy each second (in the form of heat) into the room? Does this mean your computer & monitor pump the same amount of energy (per second) into the room as a 300 watt electric heater?
I’m pretty sure the answer is yes. All of the energy must eventually end up as heat. Even the light emitted from the monitor gets absorbed by the walls and turned into the heat. I would think the only heat that “escapes” the room would be electromagnetic energy that passes through a window and goes off into space.
If you’re just looking at the motor, then no. Some of the power is turned into kinetic energy of the moving air, and the rest is turned into heat.
However, for a household space heater, the moving air stays in the room, and its kinetic energy eventually gets converted into heat within the room.
Anyway… If you think of a heater as a device for making you feel warm, then you could define “efficiency” in terms of how much power it uses to make you comfortably warm. A whole-house A/C is very inefficient in that respect. A space heater in a small room is better. An electric blanket is even more efficient because very little power is wasted in heating up the room itself (walls, furniture, etc). I imagine a Japanese kotatsu is even better.
However I’m not very sure about oil-filled radiator vs. fan heater. “Radiators,” despite the name, mostly rely on natural convection to distribute heat throughout the room. I would think a fan heater blowing directly at your body would be more efficient. Then again, I guess most people don’t point their heaters directly at themselves.