Is It Better To Turn Your Air Conditioner Off or Leave it Running All Day?

An air conditioner can be a life saver in the blistering summer. But it is also one of the largest users of energy in our home. One of the most common questions I receive when I give lectures on saving money is whether it is better to turn the air conditioner off when you leave the house, or leave it running.

Photo by David Law on Unsplash

It’s a hot summer day. The house will be empty for 8-10 hours while everyone is at work or school. If you turn off the A/C before you leave, when you get home it will be hot and the unit will have to work hard to lower the temperature when you return. But if you leave it running all day, you will be paying to cool an empty house. So which is better?

Is It Better To Turn the Air Conditioner Off?

After searching the internet high and low, it was difficult to find hard data on this area. But according to the Department of Energy, you can save 10% a year on cooling costs by setting the temperature 7 to 10◦F degrees higher for 8 hours a day than one would typically have it. (The same is true for saving on heating costs in the winter.)

According to the Department of Energy, it’s true that the closer the inside temperature is to the outside temperature, the less work your unit has to do (hence the less energy it consumes) to cool your home.

However, it’s a myth that keeping a unit running all day when no one is home is better than restarting it as needed.

For this reason, programable thermostats have become quite popular. With a programable thermostat, one can set the desired temperature to be 10◦F higher during the hours you are away. Then, program the central A/C to come on again (i.e., set the desired temperature to be lower) 30 minutes before you arrive home.

Setting the A/C 10◦F higher for 8 hours per day can save up to 10% on your cooling costs.

What If you Don’t have a Programable Thermostat?

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If you do not have a programmable thermostat, you can manually set your desired temperature to 10 higher when you leave. Then return it to your usual setting when you return.

Your A/C only runs at one speed. So don’t set it colder to cool your house faster as you will only waste money by overcooling your house.

Optimal Temperature to Keep Cool and Reduce Energy Bill

Consumer Reports cites Energy Start recommendations that you should keep your home no cooler than 78◦F when at home. Once you are comfortable at 78◦F, try increasing the temperature by 1◦ at a time to see how it affects you (and your electricity bill). For every degree above 78◦ during the summer months, you can save 3% or more on monthly cooling costs.

  • 78◦ F or higher when you are at home*
  • 85◦ F when away
  • 82◦ F when asleep**

*For those of us who live in very hot climates, the 70s is sweater weather. 78◦ is also quite far off from the outside temperature. When it is in the 90s outside, I set my thermostat to 83◦ F when at home, which is still more than 10◦ cooler than it is outside.

**For those of us who need to sleep in a cold house, try lowering the temperature a degree or two at night, then raising it back up during the day.

For every degree above 78◦ F, you can save 3% or more on your monthly cooling costs in the summer.

Other Ways to Keep Our Home Cool

Photo by Lorenzo Mitil on Unsplash

In addition to your A/C and fan settings, there are other things we can all do to help keep our house cool.

  • Set ceiling fans to turn counterclockwise in summer & clockwise in the winter.
  • Turn off fans when leaving the room. Fans cool people, not rooms.
  • Cook outside on the grill.
  • Use electric pressure cooker rather than cooking on the stove.
  • Try a convection oven or microwave rather than the oven.
  • Run dishwasher either while you are away or at night.
  • Put weather stripping on doors and windows.
  • Make sure your house is properly insulated.
  • Consider an energy audit from your electric company.
  • Keep anything that puts off heat away from the thermostat.
  • Change the air filter on your A/C every 3 months, and use a good quality filter.
  • Clean your register (i.e., the grate that covers the air filter).
  • Keep South & West facing blinds and curtains closed (to keep heat out).

Related Article: 20 Best Electricity Saving Tips


One thought on “Is It Better To Turn Your Air Conditioner Off or Leave it Running All Day?”

  1. While everything you said is true and useful, some modern AC and heat pumps do actually utilize variable speed compressors so that they can run continuously and control the temperature by only running as fast as they need to based on the load. (I’m a chemical engineer but I only know this because I placed an order for a new $6,000 AC/heat pump for my house last week, and it is a variable speed unit.) However as you said turning the thermostat down way low does not speed up how fast they will cool your house down no matter what kind of compressor they have. That’s a very well explained post busting a pretty common modern myth!

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