I don't think you understand their point. Typically, heat is the only undesirable byproduct of electrical devices, so the less heat it produces, the more "efficient" it is. However, if what you want is heat, then all devices are 100% "efficient." (Minus any EM or kinetic energy that leaves the area as anything but heat)

A 100W incandescent light bulb and a 10W LED+90W heater are exactly the same in terms of how much heat they produce for how much energy they use, with the bonus that when you don't want that heat, you can turn off the 90W heater and have the same light for 10% of the energy expenditure