How to Set Air Conditioner Thermostat? | The 78°F Rule

Set your air conditioner thermostat to 78°F when home, and raise it 7–10 degrees when away to cut cooling costs.

The most widely cited target for summer cooling is 78°F while you’re home and awake. Bump that to around 85°F when the house is empty, and you’ll trim your energy bill without turning your living room into a sauna. The practical rule: set the thermostat as high as you’re comfortable, then let ceiling fans do the rest. Here’s how to dial it in correctly and avoid the mistakes that waste power.

What Temperature Should You Actually Use?

For a typical US home with central air, 78°F is the standard recommendation for occupied hours. Consumer Reports backs this figure as the best balance of comfort and efficiency for most households. When you leave for work or a trip, raising the setpoint by 7–10°F—landing near 85°F—keeps the house from becoming an oven while your AC runs far less.

Sleeping targets run a bit warmer, with 80–82°F commonly suggested for summer nights. That range works because your body cools down naturally during sleep, and a lighter sheet does the rest. The exact number that feels right depends on your insulation, local humidity, and how well your system keeps up.

How to Change the Setpoint on Your Thermostat

Most thermostats use the same basic controls. On a digital model, press the mode button until it reads COOL, then use the up and down arrows to set your target temperature. The display will show the new setpoint, and your AC will run until the room hits that number.

For a programmable thermostat, the sequence matters:

• Set the correct date and time first—a wrong clock throws off every scheduled period.
• Program each period (wake, leave, return, sleep) with its own temperature.
• Save the schedule and switch to the RUN or AUTO mode so it follows your plan.

Honeywell’s Focus Pro documentation notes that some models hide configuration options behind an installer setup menu, so if you don’t see the settings you expect, check your manual for model-specific steps. Trane’s installation literature makes the same point: options differ by thermostat type, and the manual is the final word for your unit.

Common Mistakes That Waste Energy

The most expensive error is cranking the thermostat way down to “cool faster.” Your AC produces cold air at the same rate regardless of the setpoint—dropping it to 70°F doesn’t speed anything up, it just makes the system run longer and burn more electricity. Set it where you want the room to end up and wait.

Other frequent misses include:

• Forgetting to raise the setpoint when you leave for the day.
• Confusing heating and cooling guidance—the 68°F home / 60°F away numbers are for winter, not summer.
• Ignoring humidity, which makes 78°F feel sticky in a damp climate; a dehumidifier often helps more than a lower setpoint.
• Programming a schedule without setting the clock, so the “away” period fires at the wrong hours.

Ceiling fans also deserve a mention: they make a room feel several degrees cooler by moving air across your skin, but they don’t lower the actual temperature. That’s fine—running a fan at 80°F setpoint is cheaper than running the AC at 76°F.

When the Thermostat Isn’t the Problem

If your home never reaches the setpoint, the thermostat isn’t always the culprit. A system that runs constantly without catching up may be undersized for the house, low on refrigerant, or due for a filter change. Dirty coils and clogged filters reduce airflow, which hurts both cooling and efficiency. If the unit can’t keep up, no setting will fix it—that’s a maintenance or capacity issue, not a configuration one.

These recommendations are general summer guidance, not a universal setting. Comfort, insulation, and HVAC performance all shift the ideal number. Start at 78°F and adjust one degree at a time until you find the sweet spot between your electric bill and your comfort.

If you’re in the market for a smarter unit that handles these schedules automatically, our roundup of the best air conditioner thermostats breaks down which models make programming easiest.