Why is an electric heater the only appliance that is 100 percent efficient?

Answer 1

It is difficult to believe that anything has a 100% efficiency rating, even an electric heater. Electricity is very good at producing heat. Any loss of efficiency would be in how much heat is lost to the surrounding equipment and building structure in the immediate vicinity of the heater, which may be in the basement, as opposed to heating the air in living or working areas which is probably what you want.

Electricity is very expensive when compared to other forms of heat, such as natural gas.