Here's what I have learned: There is no such thing as an energy efficient heater, because they all directly convert electricity to heat. An oil heater takes longer to warm up, but can radiate heat better which makes it better for rooms you will stay in for a longer period of time, like a bedroom. Other typical glowie heaters are quicker to warm up but don't hold the heat very well, which makes them better for rooms you won't spend much time in.