Should You Turn Off the AC When You Leave the House? What Actually Saves Energy

Adjusting home thermostat

 If you are heading to work, running errands, or leaving for the weekend, you may wonder whether it makes more sense to turn the air conditioner off completely or leave it running.

The simple answer: You usually do not need to keep your home as cool when nobody is there. Raising the thermostat while you are away can reduce unnecessary cooling, while completely shutting off the AC may not always be the best choice for every home.

The right approach depends on how long you will be gone, the weather, humidity, pets, and your cooling system.

Here is a practical way to decide.

Is It Cheaper to Turn Off the AC When You Leave?

Your air conditioner works against the heat entering your home from outside. The greater the difference between the indoor and outdoor temperatures, the more cooling your home generally requires.

That means maintaining a very cool house all afternoon while nobody is home can waste energy.

The U.S. Department of Energy recommends setting the thermostat as high as comfortably possible when you are home in summer and raising the temperature when you are sleeping or away.

So if your main goal is reducing energy use, there is usually little reason to maintain your normal occupied temperature in an empty house.

However, that does not automatically mean switching the entire system off is always the best strategy.

Turning the AC Off vs. Turning the Thermostat Up

There are two basic options when you leave home.

AC off vs thermostat up

Option 1: Turn the AC off completely

With the system off, you are not using electricity to actively cool the home while you are away.

The downside is that the indoor temperature can climb significantly on a very hot day. Humidity may also become a concern in humid climates, and the home may take time to become comfortable again after you return.

This approach may make more sense in mild weather or under circumstances where indoor heat and humidity are unlikely to become a problem.

Option 2: Raise the thermostat

Instead of turning the system off, you can set the thermostat several degrees higher than your normal comfortable temperature.

The AC will run less often but can still prevent the house from becoming excessively hot.

For many households, this is the more practical approach because it reduces cooling while maintaining some temperature control.

ENERGY STAR also recommends using thermostat settings that save energy during long periods when nobody is home.

What If You're Only Leaving for an Hour or Two?

You do not need to obsess over the thermostat every time you walk out the door.

If you are making a quick trip to the grocery store or picking someone up, constantly making large temperature changes may be more trouble than it is worth.

A small adjustment—or simply following an automatic thermostat schedule—can be easier.

For example, imagine that you normally keep your home at a comfortable setting while working from home. On a day when you will be at the office from morning until late afternoon, maintaining that same temperature in an empty house is unnecessary.

That is exactly the kind of situation where an away schedule can be useful.

What If You're Gone All Day?

A full workday gives you a much longer period in which the house does not need to be cooled for your immediate comfort.

Instead of maintaining your normal occupied setting, raise the thermostat while you are gone and schedule it to return to your preferred temperature around the time you come home.

A programmable or smart thermostat makes this much easier.

Many smart thermostats can automatically adjust cooling when the home is empty. Some also offer geofencing, which can detect when you leave and begin restoring your preferred temperature as you return.

This is one of those small household changes that is easy to overlook. It is surprisingly common to focus on turning off lights while leaving one of the home's biggest energy users operating exactly as if everyone were still home.

Should You Turn Off the AC When Leaving for Vacation?

A vacation is different from a normal workday.

If you will be gone for several days, there is no reason to cool the house for your personal comfort. However, completely shutting down cooling during very hot weather deserves more thought.

Consider:

• Outdoor temperatures
• Indoor humidity
• Pets remaining in the home
• Houseplants that may be sensitive to extreme heat
• Electronics or other belongings affected by excessive temperatures
• Recommendations for your particular HVAC system
• Any other temperature-sensitive items in the home

A thermostat's vacation or away mode can be useful here. ENERGY STAR notes that vacation modes can manage temperatures during longer absences while helping protect the home from extreme conditions.

If someone or a pet will remain in the house, energy savings should never take priority over safe indoor temperatures.

Does Turning the AC Back On Use More Energy Than Leaving It Running?

A common argument goes like this:

"If I turn the temperature up, the AC will have to work extra hard when I get home, so I might as well leave it running all day."

That reasoning can be misleading.

Your home continuously gains heat from outside during hot weather. Keeping it at a lower temperature for hours requires the AC to keep removing that heat.

Allowing the indoor temperature to rise while the house is empty reduces the temperature difference between indoors and outdoors, which can reduce the cooling required during that period.

The system may run for a while when you return, but that does not mean maintaining your normal comfort temperature all day would necessarily have used less energy.

There is also no need to set the thermostat unusually low when you get home. The Department of Energy advises against setting an air conditioner colder than normal in an attempt to cool the house faster. It does not make the home cool faster and can result in unnecessary cooling.

Don't Forget About Humidity

Temperature is not the only consideration.

In humid climates, air conditioning also helps remove moisture from indoor air. Turning the system completely off for a long period can therefore have consequences beyond coming home to a hot living room.

If high indoor humidity is a recurring problem in your home, a moderate away setting may be more sensible than shutting the cooling system down completely.

Humidity problems can also indicate issues with equipment operation, sizing, or ductwork, so persistent problems may deserve professional attention.

What About Pets?

If a dog, cat, or another pet stays home, do not choose an away temperature based only on your electric bill.

Pets vary considerably in their ability to tolerate heat. Age, breed, health, humidity, ventilation, access to water, and the actual indoor temperature all matter.

Instead of using a universal temperature recommendation, choose an indoor environment that is safe for your specific pet. If you are unsure, ask your veterinarian.

The same principle applies when children, older adults, or people with health conditions are at home: comfort and safety come before energy savings.

A Smart Thermostat Can Make This Almost Automatic

You do not need a smart thermostat to save energy, but one can make away settings easier.

Smart thermostat away mode

Depending on the model, smart thermostats may offer:

• Automatic home and away schedules
• Remote temperature control
• Geofencing
• Vacation modes
• Occupancy sensing
• Energy-use information

If your daily schedule changes frequently, these features can be especially convenient because you do not have to remember to adjust the thermostat every time you leave.

A basic programmable thermostat can also work well if your schedule is predictable.

Other Ways to Keep the House Cooler While You're Away

Your thermostat is only part of the equation.

Before leaving on a hot day, you can also reduce the amount of heat entering or being generated inside your home.

Close blinds or curtains on sunny windows

Direct sunlight can add significant heat to a room. Window coverings can help block some of that solar heat, especially on windows receiving strong sun.

Turn off unnecessary lights

Lights generate heat as well as use electricity. There is little reason to leave them on throughout an empty house.

Avoid leaving heat-producing devices running unnecessarily

Electronics and appliances can contribute heat indoors. Turning off equipment you do not need can reduce both direct electricity use and unwanted heat.

Maintain your cooling system

A neglected air conditioner may operate less efficiently. Filters should be checked and replaced or cleaned according to the system and manufacturer's recommendations.

ENERGY STAR also recommends regular HVAC maintenance to help equipment perform properly.

Use ceiling fans only when someone is there

This one is easy to get wrong.

Ceiling fans make people feel cooler by moving air across the skin; they do not meaningfully cool an empty room. Turn them off when you leave the room instead of running them all day for an empty house.

A Simple Example

Suppose you normally keep your home at a comfortable temperature in the evening, but everyone leaves around 8 a.m. and returns at 6 p.m.

You have three choices:

1. Maintain the same comfortable temperature for all 10 hours.
2. Turn the cooling system completely off.
3. Raise the thermostat while the house is empty and have it return toward your preferred setting before you arrive home.

For many households, the third option provides a practical balance between energy use and comfort.

The exact setting will depend on the home, climate, humidity, occupants, pets, and HVAC system, so there is no single temperature that is ideal for everyone.

Common Mistakes to Avoid

Keeping an empty house at your normal comfort temperature: You are paying to maintain comfort for people who are not there.

Turning the thermostat extremely low when you return: A lower setting does not make a typical AC cool the home faster.

Leaving ceiling fans running in empty rooms: Fans cool people through air movement, not the room itself.

Ignoring humidity: In humid regions, completely shutting off cooling for long periods may create problems.

Using the same strategy in every situation: Leaving for 30 minutes, working away from home for 10 hours, and taking a two-week vacation are different situations.

The Bottom Line

You generally do not need to cool an empty house to the same temperature you prefer when you are home.

For a normal workday or several hours away, raising the thermostat is often a practical strategy. It reduces unnecessary cooling without giving up all control over indoor temperature and humidity.

For longer trips, you can use a larger setback or vacation mode, but consider climate, humidity, pets, plants, and anything else in the home that may be affected by excessive heat.

And when you return, resist the temptation to crank the thermostat far below your normal setting. Set it where you actually want it and let the system do its job.

FAQ

Should I turn my AC off every time I leave the house?

Not necessarily. For short trips, making a major adjustment may provide little practical benefit. For longer absences, raising the thermostat can reduce unnecessary cooling.

Is it better to turn the AC off or leave it on while at work?

For many homes, raising the thermostat while you are at work is a practical middle ground. The system cools less while the house is empty but can still manage indoor temperature.

Will setting my AC colder cool the house faster when I get home?

No. Setting a typical air conditioner lower than your desired temperature does not make it cool the home faster. It can instead cause the system to keep cooling longer than necessary.

Should I leave ceiling fans on while I'm away?

No. Ceiling fans primarily make people feel cooler through moving air. ENERGY STAR recommends turning them off when the room is unoccupied.

What should I set my AC to when I go on vacation?

There is no universal setting that works for every home. Consider your climate, humidity, pets, plants, HVAC system, and anything temperature-sensitive in the house. A vacation or away mode can make managing longer absences easier.