Should You Turn Your AC Up When You're Not Home?

woman going to yoga class — The best thing to do when leaving home for a few hours is to turn up the thermostat. The Good Brigade/Getty Images

Key Takeaways

It's more energy-efficient to keep your AC on but set a few degrees higher when you're away from home for the day. Completely turning it off doesn't necessarily save energy as the unit will have to run longer to cool down a hot house upon your return.
In hot and humid climates, keeping the AC on but at a higher temperature is also important for reducing humidity levels inside the home, which can prevent mold growth and protect electronic items and wood from damage.
Turning the AC temperature down to a very low setting upon returning home won't cool the house faster but will increase your energy bill, so it's best to maintain a moderate setting.

In these times of ridiculous inflation and over-the-top gas prices, many consumers are looking to save a buck or two wherever they can. Energy costs money, and the more you use it the higher the bill is going to be. In fact, air conditioners account for 6 percent of U.S. electricity costs per year, which is about $29 billion, according to the U.S. Dept. of Energy (DOE).

We know running the air conditioning unit all the time is expensive, but will you save money and energy by keeping it at the same temperature continuously, or by raising it higher when you're out of the house?

A lot depends on how long you'll be gone. Let's find out the best strategies with the help of Logan Kureczka, lead communications consultant at Duke Energy in North Carolina.

Contents

If You're Leaving Home for the Day or Weekend ...
If You're Leaving Home for a Longer Period ...
While You're in the Home...

If You're Leaving Home for the Day or Weekend ...

Don't turn off the unit entirely if you're simply going to work. "If you're just leaving home for the day, it's more energy efficient to keep your air conditioning turned on – but turn it a few degrees higher than you might set it for comfort if you were at home," Kureczka says via email.

The same directions apply if the house is going to be unoccupied for only a day or two. "It's more energy efficient to keep the unit on but turn the temperature setting up," she advises.

Turning off the AC unit during the day is not necessarily a bad thing — it is a myth that the AC unit has to work extra-hard to cool off a hot house. It runs at the same speed either way — it just will have to stay on longer to cool off a hot dwelling. In fact, the unit may use more energy if it is left on all day at the normal temperature than if you turned it off and turned it on in the evening.

That said, if you live in a hot climate, it could take several hours to cool off your house by which time you may be ready for bed. Also, central air conditioning is not just about cooling your space. It also drastically reduces humidity levels. When the system is shut off for more than a few hours, the humidity level will start to rise, which can result in mold growth, damage to electronic items and the warping of wood and paper. Any pets left in the house could also be at risk of overheating and discomfort. This is especially likely in hot, humid climates, like Florida's.

This is why it's recommended to keep the AC on but raised to a higher temperature. The DOE points out that a higher interior temperature actually slows the flow of heat into your house, thus saving energy and money.

When you get back home, don't turn the AC super-low to "speed up" the cooling process. Your home won't cool any faster and you'll just add to your energy bill.

If You're Leaving Home for a Longer Period ...

If the entire household (pets included) are vacating the premises for more than two days, it's an option to go ahead and turn everything off. "You'll save the most energy — and save on your bill — by turning your unit off," says Kureczka.

That said, the internal temperature might not be pretty when you get back. Avoid coming home to a sweltering abode by installing a smart thermostat. "Investing in a programmable or smart thermostat is a great way to monitor and control your home's energy efficiency even when you're not there – you can turn the thermostat up before leaving and then begin to cool it down when you're on your way home," she explains.

She also suggests closing the curtains if you're gone for more than a few hours. This will effectively block out the afternoon sun, so that your air conditioning unit doesn't have to work so hard to stay ahead of the heat. In areas that see extreme temperatures, this makes an enormous difference.

While You're in the Home...

EnergyStar (a program run by the DOE and Environmental Protection Agency) recommends keeping your thermostat at 78 degrees Fahrenheit (28 degrees Celsius) or higher in the day, 82 F (28 C) for sleeping and 85 F (29 C) when you're away from home. Do these temps seem too high to you? Cooling your home to 78 degrees rather than 72 could cut your electricity bill by 25 percent.

Kureczka has a slightly different take on the thermostat issue: "Raise it as high as you can while still remaining comfortable – this will vary by individual. As a rule, raising the temperature by just 2 degrees will help reduce cooling costs by 5 percent," she says.

A few other measures can make a big difference in overall climate-related comfort, particularly if you've decided to raise the thermostat higher than you're used to. One is to make use of ceiling fans. "Remember, though, that fans cool people; they don't change the temperature," Kureczka explains. "So, turn them off when you leave the room." Otherwise, you'll be paying to power that appliance unnecessarily.

Anyone who has trouble sleeping in 80 degree-plus temps can also use lighter bedding and sleep clothes and invest in "cooling" sheets to adjust to the difference.

Finally make sure your home is properly insulated so cold air is not escaping out and warm air is not creeping in.

Frequently Asked Questions

What are the benefits of using a programmable thermostat with your AC system?

A programmable thermostat can automatically adjust the temperature based on your schedule, ensuring energy efficiency without manual adjustments.

How can I maintain a comfortable temperature for pets at home while saving energy?

Keeping the AC on at a slightly higher temperature while you're away can ensure a comfortable environment for pets without significantly increasing energy costs.