Best AC Temperature for Summer: Settings That Balance Comfort and Cost
The best AC temperature for summer is 78°F (25.5°C) when you’re home and awake, according to the U.S. Department of Energy. Higher when you’re out, and adjusted to preference while sleeping.
That number surprises people who keep their homes at 72°F. It’s worth knowing where it comes from and why the exact figure matters less than the habits around it.
Each degree you raise your setpoint reduces cooling costs, and the savings compound over a long season. But comfort matters too, and there’s a more useful way to think about this than chasing a single number.
Recommended Settings at a Glance
| Situation | Recommended Setting |
|---|---|
| Home and awake | 78°F / 25.5°C |
| Away for the day | 85°F / 29.5°C |
| Sleeping | 65 – 72°F / 18 – 22°C |
| Away for a week or more | 85°F / 29.5°C, don’t turn off |
| Humid climate | 76 – 78°F with dehumidification |
Note: these are starting points, not rules. The right setting is the highest temperature at which you’re comfortable, and that varies by person, humidity and what you’re doing.
Where 78°F Comes From
The Department of Energy recommends 78°F as a balance point between comfort and energy use for a typical home with a typical occupant.
It’s not a magic number. It’s a reasonable compromise, and it assumes moderate humidity and normal indoor clothing. Someone in a humid climate might need 76°F to feel equally comfortable, while someone in a dry climate might be fine at 80°F.
The useful principle behind it: the smaller the difference between indoor and outdoor temperature, the less your system runs and the less it costs. Every degree closer to outdoor temperature reduces the work your AC does.
What Each Degree Actually Saves
This is where the practical value is.
As a general rule, each degree you raise your thermostat in summer reduces cooling energy use by roughly 3 to 5 percent. The exact figure varies with climate, insulation and system efficiency, but the direction is consistent.
Worked Example
A household spending $200 a month on cooling, currently set at 72°F:
| New Setting | Approximate Monthly Saving |
|---|---|
| 74°F | $12 – $20 |
| 76°F | $24 – $40 |
| 78°F | $36 – $60 |
Over a four-month cooling season, moving from 72°F to 78°F could save somewhere between $144 and $240 in this example.
Important caveat: these are estimates based on typical percentages. Your actual savings depend on your climate, your home’s insulation, your system’s efficiency and your utility rate. The way to know your real numbers is to change the setting and compare bills across similar weather.
Settings by Situation
When You’re Home
Start at 78°F and adjust downward only if you’re genuinely uncomfortable. Many people find they adapt within a few days, especially with a fan running.
Ceiling fans change the math significantly. Moving air makes a room feel roughly 4°F cooler than it is, which means you can set the thermostat higher for the same comfort. A fan costs a fraction of what an air conditioner does to run.
The key point about fans: they cool people, not rooms. Turn them off when you leave, since a fan running in an empty room is purely wasted electricity.
When You’re Away
Raise the setting to about 85°F rather than turning the system off entirely.
Why not off? In humid climates, a house with no cooling for hours accumulates moisture, which can encourage mold growth and makes the space harder to cool down when you return. Keeping some cooling maintains reasonable humidity.
Does it cost more to cool a warm house back down? This is a persistent myth. Your system doesn’t work harder to recover than it would have to maintain the lower temperature all day. The energy required to cool the house back down is less than the energy saved by not cooling an empty house for eight hours.
A programmable or smart thermostat handles this automatically, raising the temperature when you leave and starting recovery before you return.
While Sleeping
Here the guidance diverges from pure energy efficiency, because sleep quality matters.
Sleep research generally supports a cooler bedroom, in the range of 65 to 72°F, because core body temperature drops during sleep and a cool room supports that.
That’s lower than the daytime recommendation, which means it costs more. Options that reduce the cost:
- Cool only the bedroom with a ductless unit or window AC rather than the whole house
- Use a fan to allow a higher setpoint with equivalent comfort
- Program a gradual rise in the early morning hours
There’s a real tradeoff here between energy savings and sleep quality, and sleep usually wins that argument.
On Vacation
For absences of several days or more, 85°F with the system still running is the standard recommendation.
Turning the system off entirely in a humid climate risks moisture problems, particularly in a closed house with no air movement. In dry climates, the risk is lower but a very hot house is hard on some furnishings and electronics.
Why Humidity Changes Everything
Two homes at the same temperature can feel entirely different depending on humidity.
At 50 percent relative humidity, 78°F feels comfortable to most people. At 70 percent, the same temperature feels warm and sticky, because your body’s evaporative cooling doesn’t work as well.
The practical implication: if 78°F feels uncomfortable in your home, humidity may be the problem rather than temperature. Addressing humidity often lets you raise the thermostat several degrees while feeling equally comfortable, which saves more than lowering the temperature would have cost.
Target humidity in summer is 40 to 50 percent. A hygrometer costs $10 to $25 and tells you where you stand. Our indoor air quality guide covers humidity management in detail.
A system that short cycles won’t dehumidify well, since moisture removal requires sustained runtime. If your house is cool but clammy, see our guide on AC short cycling.
Common Mistakes
Setting the thermostat very low to cool faster. Your AC cools at one rate regardless of the setpoint. Setting it to 65°F when you want 75°F doesn’t accelerate anything, it just means the system runs past your target and wastes energy.
Turning the system off completely when leaving. Discussed above; in humid climates this creates moisture problems and doesn’t save as much as raising the setpoint does.
Closing vents in unused rooms. This raises static pressure in the duct system, reduces airflow across the coil, and can cause freezing and short cycling. Modern systems are designed for the full duct network to be open.
Leaving fans running in empty rooms. Fans cool people through air movement across skin. In an empty room they add a small amount of heat from the motor and accomplish nothing.
Ignoring the thermostat’s location. A thermostat in direct sun, above a lamp, or near a supply vent reads incorrectly and makes the whole system respond to bad information.
Beyond the Thermostat
Several things let you stay comfortable at a higher setting.
Block direct sun. Closing blinds or curtains on sun-facing windows during the hottest hours reduces heat gain substantially. West-facing windows in the afternoon are the biggest contributor in most homes.
Use exhaust fans while cooking and showering. Both add heat and moisture directly.
Run heat-generating appliances in the evening. Ovens, dryers and dishwashers add heat that your AC then has to remove.
Keep your system maintained. A dirty filter or fouled coil means your system delivers less cooling for the same electricity, which affects what setting feels comfortable. Our AC maintenance guide covers the schedule.
Address air leaks and insulation. These determine how hard your system has to work to hold any setting.
Our guide on how to cool a room without AC covers more of these approaches.
Programmable and Smart Thermostats
The savings from adjusting your setting only materialize if the adjustments actually happen.
A programmable thermostat automates the pattern: higher while you’re out, comfortable when you’re home, adjusted overnight. Smart thermostats add geofencing, learning, and remote control.
What to look for: the ability to set different schedules for weekdays and weekends, a recovery feature that starts cooling before your scheduled arrival rather than at it, and compatibility with your system, which matters particularly for heat pumps and multi-stage equipment.
A note on savings claims: manufacturers cite substantial percentage savings, but those assume you weren’t already adjusting your thermostat manually. If you already turn it up when leaving, the incremental benefit is smaller. Our thermostat settings guide covers this in more detail.
Frequently Asked Questions
What is the best AC temperature for summer?
The Department of Energy recommends 78°F (25.5°C) when you’re home and awake, 85°F when away, and a cooler setting for sleeping. The practical principle is to set it as high as you find comfortable, since every degree closer to outdoor temperature reduces cooling costs.
How much does each degree save on AC?
Roughly 3 to 5 percent of cooling energy per degree, though this varies with climate, insulation and system efficiency. On a $200 monthly cooling bill, raising the setting from 72°F to 78°F might save $36 to $60 per month.
Is 72 degrees too cold for AC in summer?
Not unsafe, but it’s expensive. At 72°F your system works considerably harder than at 78°F, and the difference across a full cooling season is substantial. If 78°F feels uncomfortable, humidity is often the actual problem rather than temperature.
Should I turn my AC off when I leave the house?
For normal daily absences, raise the setting to about 85°F rather than turning it off. In humid climates, an unconditioned house accumulates moisture that can encourage mold and makes recovery harder. The energy saved by turning it off completely is minimal compared with simply raising the setpoint.
What temperature should I set my AC at night?
Sleep research supports 65 to 72°F for sleep quality, which is cooler than the daytime energy recommendation. This is a genuine tradeoff. Cooling only the bedroom, or using a fan to allow a higher setting, reduces the cost.
Does setting the thermostat lower cool the house faster?
No. Your air conditioner cools at a fixed rate regardless of the setpoint. Setting it to 65°F when you want 75°F doesn’t speed anything up; it just means the system keeps running past your actual target.
Why does 78 degrees feel hot in my house?
Usually humidity. At 70 percent relative humidity, 78°F feels considerably warmer than the same temperature at 45 percent, because evaporative cooling from your skin is less effective. Measuring humidity with a hygrometer and addressing it often lets you raise the thermostat comfortably.
What temperature should I set my AC when on vacation?
About 85°F with the system still running. This maintains reasonable humidity without cooling an empty house, and avoids the moisture problems that come from shutting the system off entirely for days in a humid climate.
Bottom Line
Start at 78°F when you’re home, 85°F when you’re out, and whatever supports your sleep at night. Each degree higher saves roughly 3 to 5 percent on cooling.
If 78°F feels uncomfortable, check humidity before lowering the temperature. Getting humidity into the 40 to 50 percent range often makes a higher setting feel fine, and costs less than cooling further.
And use ceiling fans in rooms you’re actually in. They let you set the thermostat several degrees higher for the same comfort, at a fraction of the running cost.