Common joke says that heaters are 100% effient because all they make is heat. How much energy is actually lost?
In: Physics
A machine is a tool designed to take energy in one form and convert it to other forms in order to do something useful with it – whether this is an electrical device or purely mechanical. A bike takes kinetic energy from your leg movements and converts it to rotational energy in a wheel. A fan takes electric energy and converts it to rotational kinetic energy for the fan blade to push air. A heater takes electric energy and converts it to heat using a heating element.
No machine is 100% efficient, because of **resistance**. When electricity passes through a wire, the wire naturally resists this somewhat, and heats up. When a machine part vibrates, it pushes against the air, experiencing air resistance and creating sound. When moving machine parts make contact with each other, **friction** (another type of resistance) causes some kinetic energy to be lost to heat and sound. Some machines emit light, either on purpose for some display indicator, or as a waste by-product of other events such as friction (eg. sparks from a collision, or metal glowing as it heats up).
So a machine will always produce waste heat, light, and sound. But, what happens to sound as it travels? It causes friction in the air, which gradually converts that energy to heat. When it hits a wall, some of it bounces off (echo) and some gets absorbed as heat. The same thing happens to light. Eventually, all forms of energy become heat.
So an electric heater, which is designed to output heat, “wastes” some of its energy into light or sound which will also eventually turn into heat, so yes it is technically 100% efficient *eventually*. That doesn’t mean all heaters are equal though, because another important factor is where that heat ends up. While it’s true that any waste sound or light will eventually become heat, that’s not useful if the waste sound is absorbed by the walls and radiated externally, or waste light literally goes out the window and heats up your back fence.
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