But you are clueless how these heaters are designed and engineered which makes your MSEE worthless.
Do you know how to recognize an ignorant person in thirty seconds or less? Read your own posts.
Unfortunately for science and me, this forum has only teachers of languages and poets - neither activity depending on physics, math, and logic - so I am not able to send you to them for a quick course on what happens to the energy once it's drawn from the wall socket.
So, here is the shortest course for the ignorant: ALL ENERGY DRAWN FROM THE WALL SOCKET TURNS INTO HEAT - 100%, ALL THE TIME.
Some of it escapes the house through the walls, ceiling and the windows as radiation and convection. A completely insulated, lossless room would burst into flames as the process of drawing energy from wall - with none able to escape - would cause the temperature to rise to infinity.
In that sense, EVERY single device you plug into the wall socket is a 100% energy efficient. No exceptions. If you know of a device that can take in X and put out Y, Y being less than X, name it. After that, please, explain what happens to the difference X-Y. Like where does it go.
Can you confirm that (1) you read the above and (2) that you at least understand the words, if not the concepts.
Is there anyone here with an engineering degree? Are you all in liberal arts?