Can we please, please get our terminology correct!

Efficiency is not the same as Effectiveness. And for heat transfer systems the two, admittedly similar sounding, words refer to VERY different properties.

Any resistive electrical to thermal energy conversion system is intrinsically 100% efficient at turning electricity into heat energy. However, that 100% Efficient system could actually be 0% EFFECTIVE. For example, consider a coil of wire, heated by current passing through it. Now put that coil of wire in a vacuum effectively stopping convection and conduction, what happens to the wire? The answer is, it probably melts! If you put 100W of electrical energy in, the resistance of that wire turns that into 100 watts of heat, and if that heat cannot escape as fast as it is being put in, the temperature of the wire will climb, eventually till it melts. This is because thermal transfer is driven by the thermal impedance AND the difference in temperature. This should be obvious!

So, for a system to say heat a house, what actually matters?

Well we do want the greatest efficiency possible, ie for every watt we put in (in whatever form) we get a watt of heat out. Well, hurrah, resistive electrical heaters are 100% efficient, so happy days, that one is solved

And Effectiveness? This governs is the maximum heat flux (heating power) that can be driven out of the heater into it's environment for any given temperature difference. Given that we don't want our heater to have to run at say the temperature of the sun (which manages to drive heat across millions of miles of space to burn your nose as you sit on a beach in summer....), or our heater to be larger than a car, high effectiveness is useful, but it DOES not change the efficiency of the system at all!

So please, can we stop saying "efficient" when we mean "effective"......