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To dispense with a pet peeve of mine at the start, heat is a process of energy transfer, distinct from another process called work. What the meme should say is that the other energy is converted to thermal energy, a form of energy produced during the process of heating something up.

Numerous commenters refused to believe that heaters could be 100% efficient because they had learned that some energy is "lost" when it is converted from one form to another. It was clear what they meant is that a certain amount of energy would disappear, a clear violation of the law of conservation of energy. These commenters remind us that students will cheerfully hold conflicting ideas in their minds until teachers force examination of the conflict, and that describing energy as "lost" is perhaps not the best choice of words.

Some commenters referred to sound or light emitted from the heater as "wasted" energy. I countered that sound is just organized thermal energy, which would disorganize soon enough and warm the room. And that light from the element of a heater, if it did not go out a window, would be absorbed by the air or by surfaces in the room, and converted to thermal energy. Now we had begun to get to the heart of the matter.

There is no law of physics that requires energy to be "lost" or "wasted" during energy transfers. Earth has been orbiting the Sun for over 4 billion years, with continuous transfers of kinetic energy to gravitational potential energy and back. The second law of thermodynamics refers specifically to entropy, the concept that not all of the thermal energy available to a heat engine can be converted to mechanical energy. As a practical matter, devices with moving parts (and that includes electrons moving in a wire) are subject to friction, which produces thermal energy from kinetic energy and reduces the efficiency of the device.

Most of us would agree that the purpose of a heater is to heat the air in a room. If that is our definition of the outcome, it's tough to argue that the heater is significantly less than 100% efficient. Even a vortex heater which emits no light and circulates air across its elements will itself be warmed, and that warmth will eventually dissipate to the room. To find sources of inefficiency, we would need to follow the source of the electrical current being used by the heater until the wires carrying it are not in the room. I suppose one could argue that thermal energy absorbed by objects in the room and not the air inside it constitutes loss. As is often the case in physics, the definition of what is inside the system vs. what is part of the environment outside the system determines the mathematical process and outcome.