eli5: If most electronic appliances’ efficiency losses are through heat, does that mean that electric heaters are 100% efficient?



Many thanks for your input everyone!

Just to clarify, I don’t want to take into account the method of generating electricity or shipping it to the home, or the relative costs of gas and electricity. I just want to look at the heater itself! i.e. does 1500W of input into a heater produce 1500W of heat, for example? Or are there other losses I haven’t thought of. Heat pumps are off-topic.

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22 Answers

Anonymous 0 Comments

Yes, electric heaters convert 100% of the power that they consume into heat. So they have an efficiency of 100%.

Heat pumps move heat from one area (outside your house) to another area (inside your house) The amount of heat they move is typically about 3 times more than the power they consume. So the in terms of energy-to-heat efficiency, they are 300%+ efficient.

But thermodynamically they are not “creating” heat from nothing. So heat pumps are not perpetual motion machines, they don’t break any of the laws of thermodynamics.

Anonymous 0 Comments

In terms of converting electricity to heat, yes nearly 100% minus the power for the circuit board and loses through traveling the wire. But heat doesnt necessarily mean heat towards heating up your room. It could be heat that’s generated internal to the heater and dissipated before it makes any impact to your room.

Anonymous 0 Comments


Funny thing is, there are heating devices (heat pumps) that are more than 100% efficient. They steal heat from their cold source, using less energy than they give off on the side of their hot source.

Anonymous 0 Comments

Pretty much. There’s negligible energy lost to other sources – sound, for example if it makes any noise, but basically 100% efficient.

In a similar vein – the old incandescent light bulbs were about 98% efficient, if you used them for heating…

This doesn’t mean electric heaters are necessarily the best way to heat a house using electricity. Provided the temperature difference to outside isn’t too much (outside isn’t much below freezing) heat pumps are much more efficient at heating a space because they use thermodynamic wizardry to *move* rather than *create* heat and can move more heat into your house than an electric heater of the same power could produce.

Anonymous 0 Comments


Anonymous 0 Comments

Yes, and it goes even further. Almost any device in your home is a almost 100% efficient heater. All of the energy that does not directly get converted into heat will eventually be too, once the emmited light & sound are absorbed and any motion dissipates its energy by friction into heat.

Anonymous 0 Comments

To add to it… Technically it’s not losses through heat..
Electricity traveling through wires meets resistance.. and the resistance to electricity flow causes heat..

An analogy is when you work hard you get warmer.. the more resistance you have the more “work” electricity has to do and you lose energy due ti resistance and that causes heat..

that in it self is the loss.. ideally there’d be no resistance but we haven’t figured out how to make superconductors at room temperature yet.

There’s no such thing as 100% conversion.. that’s be a perpetual motion machine

Anonymous 0 Comments

Sure are! Even the energy that doesn’t reach the heating element turn into heat. It’s paltry by comparison, but the heat in the cord delivering power escapes into the room it’s plugged into also. This actually leads to a protip: when you’re shopping for heaters, as long as they are the same wattage, the real big expensive ones work exactly the same as the smaller cheaper ones. The expensive ones with fans might actually heat the room faster because of the forced convection, but the cheaper one is consuming the same amount of power and will eventually heat the room to same temperature.

Anonymous 0 Comments

Yes. This is a great rant on space heater misleading advertisement (and a great YouTube channel in general):

Anonymous 0 Comments

All forms of energy end up 100% heat. If your goal is to heat the only way you get less than 100% efficient is if you need an exhaust (like a chimney) to get rid of bad hot gasses. Hot means above absolute zero. In physics this is from the 2nd law of thermodynamics or entropy.