What’s The Difference Between Energy Efficiency and Efficacy?

April 3, 2015

OK, class. Open your books. It’s time to get confused.

Today’s question is: What’s the difference between energy efficiency and energy efficacy? We at Capitol Machine will attempt to explain the difference between the two.

For starters, efficiency is the output of energy divided by the input of energy. You may calculate this with long-hand division or by using your calculator. The larger the number the more value you’re getting on your investment.

Efficacy is a little more complicated. And its definition is similar to efficiency, but, alas, it is different.  Efficacy is when you put energy into something with the expectation of getting something completely different out. For instance, electrical energy goes into one of our insulation blowers; a different type of power – air flow – comes out.

Another example: The principle applies also to electric lights. By plugging a light into the wall outlet, electricity (watts) enters the lamp, but light – in Lumens – come out.



Capitol Machine: Now Open Your Math Book

Here’s some more arithmetic – and hopefully some additional clarification. (Get it? “Additional clarification”?) The efficiency rating is calculated as a ratio with numeric values on both sides of the fraction. The answer is also a number, which equates to a measurement of energy.

Here’s how efficiency works for a heater, for example. Efficiency is measured as Annual Fuel Utilization Efficiency (AFUE), which is the BTU of heat for a certain-sized room divided by the BTUs required to burn the fuel. BTU stands for British Thermal Unit.

Efficacy is useful in referring to what’s called the output quantity of a mechanism or unit requiring energy use. However, when gauging energy output in cases involving heating and cooling, it makes better mathematical sense to consider efficiency which helps us determine total energy output.

Are you still with us?


Capitol Machine: Let’s Open Our Language Book

Linguistically, efficacy refers to effectiveness, which is the ability of a machine or appliance to produce a specific result.

Efficiency refers to the ability to perform well without wasting time, money or energy.

We at Capitol Machine certainly understand that grasping technical concepts involving saving money and using machinery efficiently and efficaciously can be a challenge. But we urge you not to fret. The exam is not scheduled until next week. Did you find this classroom discussion helpful? Do you have tips of your own or any questions?

We at Capitol Machine offer a wide variety of insulation machines, insulation blowers and insulation removal vacuums. We also have the experience and knowhow to make your work effective, productive and safe. We also have a pretty grasp on what efficiency and efficacy mean? Contact us with questions or for more information.