The best thermostat setting for summer, for most US homes, is 78°F (about 26°C) when you’re home and awake, and several degrees warmer when you’re away or asleep. That’s the setting the U.S. Department of Energy points to for balancing comfort and cost, and every degree you can comfortably go above your usual setting trims your cooling bill. Below are the settings, the math behind the savings, and the cases where you should not push the temperature up.

Quick answer: summer thermostat settings

Situation	Suggested setting	Why
Home and awake	78°F	DOE’s suggested target for comfort vs. cost
Away at work (4+ hours)	82–85°F	A higher “setback” while no one is home saves the most
Sleeping	80–82°F, with a fan	Many people sleep fine slightly warmer with moving air
On vacation	85°F (or AC off in mild, dry climates)	Keeps humidity in check without cooling an empty house
Ceiling fan running	Raise your setting ~4°F	Moving air feels cooler, so you can set the AC higher
Elderly, infants, or health concerns at home	Comfort and safety first	Don’t let indoor heat build up for vulnerable people

Key takeaway: the biggest savings come not from one perfect number but from raising the setpoint whenever the house is empty or everyone is asleep.

Why 78°F is the number you keep hearing

The U.S. Department of Energy (energy.gov) suggests setting your thermostat to 78°F when you’re at home and need cooling. A widely shared ENERGY STAR heating and cooling guide went further, suggesting 78°F at home, around 85°F when away, and about 82°F while sleeping.

Those numbers aren’t magic. They reflect a simple fact: your air conditioner works harder the bigger the gap between the indoor temperature you want and the heat outside. Shrinking that gap even a little reduces how long the compressor runs, and run time is what you pay for.

If 78°F feels too warm at first, don’t jump straight there. Move up one degree every few days and let your body adjust. Plenty of people who started at 72°F end up comfortable at 76–78°F with a fan running.

How much money each degree saves

According to the DOE, you can save as much as 10% a year on heating and cooling by turning your thermostat back 7–10°F for eight hours a day from its normal setting. Many utilities and HVAC companies also use a rougher rule of thumb: each degree warmer saves a few percent on cooling costs. Treat that as a ballpark, not a promise. Real savings depend on your climate, insulation, AC efficiency and rates.

Worked example: a typical central AC

Let’s put real numbers on it. According to the U.S. EIA, the average US residential electricity price was about 18.3¢ per kWh in July 2026 (your own rate may be quite a bit higher or lower).

Assume a 3-ton central air conditioner that draws about 3 kW while running:

• Hot summer day, set at 72°F: the AC runs about 10 hours
  3 kW × 10 h = 30 kWh × $0.183 = $5.49 per day
• Same day, set at 78°F: run time drops to roughly 8 hours (an illustrative estimate)
  3 kW × 8 h = 24 kWh × $0.183 = $4.39 per day

That’s about $1.10 a day, or roughly $33 over a 30-day hot spell, from six degrees. Over a three-month cooling season, that adds up to around $100. In hotter, longer summers (think Texas, Arizona or Florida) the figure can be considerably higher.

Worked example: a daytime setback

Now say nobody is home from 8 a.m. to 5 p.m. If you let the house drift up to 85°F during that window instead of holding 78°F, the AC might run, say, two or three fewer hours on a hot day:

• 3 kW × 2.5 h = 7.5 kWh × $0.183 = about $1.37 saved per workday
• × 22 workdays = about $30 a month

Again, these are estimates to show the scale, not guarantees. The point is that setbacks while you’re out often save as much as, or more than, the at-home setting itself.

Does turning the AC up while you’re away really save money?

Yes, in almost every case. A common myth says it’s cheaper to keep the house at one temperature all day because the AC “works harder” to cool it back down. The DOE says the opposite: a warmer house gains heat from outdoors more slowly, because the temperature gap is smaller, so your AC uses less energy in total even counting the cool-down.

A few practical points:

• Time the cool-down. Set the thermostat to start cooling 30–60 minutes before you get home, so you walk into a comfortable house.
• Don’t set it lower to cool faster. Setting 65°F won’t make most systems cool any faster than 78°F; it just means the AC keeps running past the temperature you actually wanted. The DOE warns against this too.
• Very hot, humid climates: a smaller setback (around 4–7°F) may make more sense, because letting humidity build up all day can make the house feel clammy when you return.

If you’re doing this by hand every morning, a programmable or smart thermostat makes it automatic. See our guide to smart thermostat savings to decide whether one is worth it for you.

Best settings at night

Sleep is where personal comfort matters most, so there’s no single rule. Many people sleep well at 80–82°F with a ceiling fan or bedside fan running. Others need it cooler. Two tips:

1. Use a fan instead of a lower setpoint. The DOE notes that a ceiling fan lets you raise the thermostat about 4°F with no loss of comfort. A ceiling fan typically uses far less power than central AC, often under 100 watts.
2. Switch off fans in empty rooms. Fans cool people, not rooms. A fan blowing in an empty bedroom just adds a little heat and cost.

Settings for heat pumps, window units and mini-splits

The same logic applies to every type of air conditioner, with a few twists:

• Heat pumps in cooling mode: setbacks work fine in summer. (In winter, large setbacks can trigger backup electric resistance heat on some systems, but that’s a heating-season issue.)
• Window AC units: use the built-in thermostat or “eco” mode rather than running on max, and close the door to the room you’re cooling.
• Ductless mini-splits: these are designed to run steadily at low speed, so moderate, gradual setpoint changes usually work better than big swings. Our window AC vs mini-split guide covers the trade-offs.

On time-of-use rates? Pre-cool before the peak

If your utility charges more in the late afternoon and evening (often around 4–9 p.m.), the timing of your cooling matters as much as the temperature. A simple strategy:

• Pre-cool the house to about 75–76°F in the early afternoon, while power is cheaper.
• Let it drift up to 79–80°F during peak hours, when every kWh costs more.
• Close blinds on sun-facing windows so the house holds its coolness longer.

How much this saves depends entirely on the gap between your peak and off-peak prices. Our explainer on time-of-use electricity rates shows how to read your rate plan.

When not to push the thermostat higher

Saving money should never come at the expense of safety. Be cautious about high indoor temperatures if your household includes:

• Older adults, infants or young children, who are more vulnerable to heat
• Anyone with a health condition that’s affected by heat (ask a doctor what’s safe)
• Pets left alone during the day, especially in very hot climates

Also watch humidity. If your home feels sticky at 78°F, the problem may be humidity rather than temperature. Indoor relative humidity is generally best kept below about 60%. A dehumidifier, or an AC that’s properly sized and maintained, can make a warmer setpoint feel much more comfortable.

Other ways to make 78°F feel cooler

Your thermostat setting works best alongside a few low-cost habits:

• Block the sun: close curtains and blinds on south- and west-facing windows during the day.
• Change the AC filter every one to three months in summer; a clogged filter makes the system work harder.
• Avoid heat-producing chores at peak heat: run the oven, dryer and dishwasher in the evening.
• Seal obvious air leaks around doors and windows so cool air stays inside.
• Keep the outdoor unit clear of leaves, plants and debris.

For more no-AC tricks, see how to keep your house cool without AC.

Frequently Asked Questions

Is 78°F too hot for a thermostat in summer?

For many people, 78°F feels comfortable with a fan running and humidity under control. If it feels too warm, try 76–77°F. Each degree still saves you something, so pick the warmest setting you’re genuinely comfortable with.

What’s a good thermostat setting when nobody is home?

Around 82–85°F is a common choice for a workday. On vacation you can go to about 85°F. In mild, dry climates some people turn the AC off entirely, but in humid areas keeping it at a high setting helps control moisture.

Is it cheaper to leave the AC on all day?

Generally no. According to the DOE, raising the thermostat while you’re out saves energy overall, even after the AC cools the house back down. A programmable or smart thermostat makes the cool-down happen before you get home.

Does the “auto” or “on” fan setting save more?

“Auto” usually saves more energy, because the blower only runs while the AC is cooling. Leaving the fan “on” all the time uses extra electricity and can put moisture back into the air in humid climates.

How much will raising my thermostat save?

It depends on your climate, home and rates. The DOE says setbacks of 7–10°F for eight hours a day can save up to 10% a year on heating and cooling. In our example, going from 72°F to 78°F saved about $1 a day on hot days.

The bottom line

The best summer thermostat setting is the warmest one you’re comfortable with. For most homes that’s about 78°F when you’re home, 82–85°F when you’re out, and a little warmer at night with a fan. The real savings come from automating those changes and pairing them with simple habits like closing blinds and changing filters. Start by raising your setting a degree or two next summer, then check your bill to see what it did for you.

Sources: U.S. Energy Information Administration, Electric Power Monthly (average residential price, July 2026); U.S. Department of Energy, energy.gov guidance on programmable thermostats and fans for cooling; ENERGY STAR heating and cooling guidance.

Figures in this guide are estimates based on typical US prices at the time of writing. Savings vary by home, climate and utility rates — check your own bill before making a purchase.

Written by The Daily Economy editorial team with AI assistance and checked against the sources above. Read our editorial policy.