Is there a space heater that is energy efficient?
Define what energy efficient is first. Thermodynamics clearly states you cannot get as much energy out as you put in so if you define energy efficiency in % as (energy out)x100/(energy in) and then claim some % or higher constitutes energy efficiency you then look for such a space heater. If you make the definition as 90% and find none at 90% or more, then the answer to your question is "no" whereas if you make the definition as 80% and find several at 81 - 85% the answer is yes. Now go out and define and search.