The U.S. Department of Energy’s answer is 78°F when you’re home, higher when you’re not. That’s the anchor. But the setpoint you hold while you’re awake isn’t where the savings live; they live in the setbacks: the 8 hours you’re at work and the 8 hours you’re asleep. Done right, DOE estimates a roughly 10% annual cut to heating and cooling from setting back 7 to 10°F for 8 hours a day.
Here’s the full cooling-season playbook.
The summer setpoint schedule (start here)
| When | Setpoint | Why |
|---|---|---|
| Home & awake | 78°F | DOE comfort/efficiency anchor |
| Asleep | 78°F (or 75-76°F with a fan on Auto) | Body cools at night; a fan lets you sit higher |
| Away (work/errands) | 85-88°F | Biggest single saver: don’t cool an empty house |
| Vacation (days away) | 85°F max, don’t turn it off | Keeps humidity in check; see below |
If 78°F feels warm at first, step down 1°F a week. Most people acclimate, and every degree you hold costs you on the bill.
Don’t power it off when you leave: set it back
The instinct on a long day out is to kill the AC. Don’t. In a humid climate a fully-off system lets indoor humidity climb past 60%, which invites mold and means the system has to wring all that moisture back out when you return, often costing more than the modest setback would have saved. Set back to 85-88°F; don’t switch to Off. A smart thermostat’s geofencing or schedule handles this automatically.
Use the schedule, not your willpower
The old “it’s cheaper to leave it at one temperature” line is a myth for cooling, too. A programmable or smart thermostat captures the away- and sleep-setbacks without you remembering to touch it. Set four periods (wake, day, evening, sleep) and let it run. If your thermostat learns or geofences, even better: it pre-empts your arrival so the house is comfortable when you walk in without holding 78°F all afternoon.
Fan: Auto, not On
Set the fan to Auto in summer. On “On,” the blower runs after the cooling cycle ends and re-evaporates moisture off the wet coil back into your rooms, leaving clammy air at the same thermostat reading. Full reasoning and the “Circulate” middle ground are in Fan On or Auto in Summer.
Watch humidity, not just temperature
If 78°F feels sticky, the problem is moisture, not heat. Target under 60% RH (40 to 50% is ideal). A thermostat with a humidity readout (or a cheap hygrometer) tells you which lever to pull. Sometimes the fix is a dehumidifier rather than colder air, which is cheaper and more comfortable than dropping the setpoint.
Advanced: pre-cool for time-of-use rates and heat waves
If your utility charges more during a peak window (often around 3 to 7 p.m.), pre-cool the house to about 74-75°F just before peak, then let it drift up to 80°F during the expensive hours. You bank the cooling at the cheap rate and coast through the costly one. The same move blunts a heat wave: get ahead of the heat in the morning instead of chasing it at 4 p.m. Full walkthrough in Pre-Cooling for Peak Rates & Heat Waves.
When the setpoint won’t hold
If the room won’t reach the number no matter how low you set it, that’s not a settings problem. Start with Why Your AC Isn’t Cooling: A Thermostat-First Checklist before you keep nudging the dial.
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The cost side of the decision
Thinking about a more efficient system rather than just better settings? Cooling upgrades, payback math, and the 2026 tax credits live on our sister site. See HomeEnergyPlanner’s HVAC tax credits & rebates and the real cost of running central air. Come back here for how to actually program whatever you install.
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The summer series: Best Temperature for AC (Day/Night/Away) · Fan On vs Auto · AC Short-Cycling · AC vs Dehumidifier · Ceiling Fan + AC · Vacation Settings
