A/C Off or On When You’re Away?

By: Brian Schutt  |  June 7, 2010

Since the invention of air conditioning this question’s been around.  What will save me more, to leave my air conditioning on when I’m away, turn up the thermostat, or turn it off completely?

A conundrum indeed.  And, one you’ve likely heard different people give different answers to.  Here are some of the variables and factors that make this not a black and white issues, but rather a custom answer for your home.

One, is the size of your home.  Smaller homes will draw less energy and take less time to cool down.

Another factor is the size, efficiency, and insulation of your system and home.  This was likely determined by whomever built your home and installed your system.  In the linked article, Bob Vila gives a thorough analysis of the impact of HVAC system size and proper insulation can have to your home energy costs.

Another, and probably the most important variable, is the outside temperature.  This is pretty basic, but if the weatherman tells you it’s going to be a high of 75 vs. a high of 85, your decision becomes easier.  If it’s 75 outside, it’s not going to get hotter inside, and thus cooling your place when you get home will not take as much time and not take as much energy.

However on those muggy 85 degree days that we face in Central Indiana, the choice may not be clear.  So, we suggest doing a little experiment.  Requirements: pen, paper, ability to read electric meter.  On two three like days do the following:

  1. Note the reading on your meter before leaving work
  2. Day 1: leave A/C at your preferred temperature (for my wife and I it’s 72 degrees)  Day 2: Turn your A/C up to a higher temperature like 80 degrees  Day 3: Turn off A/C completely.
  3. For days 2 and 3, return your thermostat to comfortable temperature on your return home.
  4. After thermostat returns to your desired temperature, or a few hours after your return home, go back to meter and note its reading.

At this point, just do the addition to see how much electricity you’ve used to get back to comfortable.  Whichever uses less energy, saves you the most money, and is the customized answer to the age old question.

* A side note and helpful hint is that for every degree above 80, you save roughly 3% on energy.  Ergo, and move from 80 to 85, should save roughly 15%.

Brian Schutt

About 

is the co-owner of Homesense Heating | Cooling. Born and raised in Indianapolis, he loves the city and its people, and is committed to bringing a servants mindset into the heating and cooling industry. One of the ways he does that is to translate the technical language of HVAC into the manageable and understandable for homeowners.

Have a question? Tweet him and you'll get an answer promptly.

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