You are correct that electric heating is 100% energy efficient in the sense that all the incoming electric energy is converted to heat. However, most electricity is produced from coal, gas, or oil generators that convert only about 30% of the fuel's energy into electricity. Because of generation and transmission losses, electric heat is more expensive than natural gas, propane, and oil. If the electric source is hydro-electric, then what you really have is solar energy. Don't forget hydro-electric starts with the sun evaporating water.