Effectiveness of electric resistance space heaters

Electric resistance heaters are 100% efficient. This statement is true but also somewhat confusing. The efficiency of turning electricity into heat is indeed 100% efficient. Often when systems have efficiencies <100% it is because there is some heat generated as an un-intentional byproduct. An electric motor in an EV for example might be 85% efficient, which means that 85% of the electric energy consumed by the motor is moving the car, the other 15% is heat. Since our electric resistance space heaters are only trying to make heat, they are 100% efficient. 

Heat pumps on the other hand can be 300-400% efficient, because they use electricity to transfer heat from outside to inside your home. This efficiency is also called the Coefficient of Performance (COP).

Another way to think about the performance of an electric resistance space heater is to look at how effective it is in warming up a room or a person. UC Berkeley's Center for the Build Environment has done decades of research in personal comfort systems, focussing on cooling or heating a person, instead of a building. For this post I'll focus on the impact of space heaters on heating up a room. 

I have evaluated two space heaters that both rely on radiation and natural convection to transfer the heat from the heater to the room and person. This is in contrast to the space heaters that have a built-in fan that blows warm air, these types of heaters use forced convection by a fan, as opposed to natural convection (buoyancy) of warm air rising up.

I've made a video that shows some of the results.

Below are a couple of graphs from the data that is shown in the video. All the raw data (~23,000 lines) is available as a CSV file here.

 This graph shows the cycling of the wall heater. This cycling happens to prevent the heater from over-heating. The heater is producing heat only about ~69% of the time. The other 31% of the time it is off. The effective output of this 1,000 W heater is only about 663 W.

The graph for the oil filled radiator shows that it only occasionally cycled off, and produced a lot more heat. It is on for 97% of the time, and off for only 3%. The effective output of this 1,500 W heater is 1,319 W.  It produces almost twice as much heat as the wall heater. It consumes more electricity, but it is more effective in heating up the room.