Indoor Climate
Ideal AC Temperature: Best Thermostat Settings for Summer
The US Department of Energy suggests 78 °F when you are home and awake in summer, with a higher setting when you are away. Many people sleep better a few degrees cooler, and keeping indoor humidity near 40 to 50% lets a warmer setting feel comfortable. The best setting is the highest one you are comfortable at.
Recommended settings at a glance
| Situation | Suggested setting | Why |
|---|---|---|
| Home and awake | About 78 °F | DOE guidance; a good balance of comfort and cost for most homes |
| Sleeping | About 70–75 °F, or as cool as you need | Many people sleep better slightly cooler; use fans to stay higher |
| Away for the workday | 4–7 °F above your home setting | Saves energy without a long recovery |
| Away for days | About 85 °F | Keeps humidity and heat stress on contents in check |
| Pets at home | No higher than about 80–82 °F | Depends on the animal; flat-faced dogs and older pets need cooler |
These are starting points. Health, age, clothing and humidity all change what feels comfortable.
Why 78 °F?
Cooling energy depends on the temperature difference between indoors and outdoors. Every degree you raise the setting reduces the heat flowing in through walls, windows and the roof, and the AC runs less to remove it. That is the basis of the DOE's 78 °F recommendation. The DOE also notes that turning the thermostat back 7 to 10 °F for 8 hours a day can save up to around 10% a year on heating and cooling.
The exact savings depend on climate, insulation and equipment. A rough rule many energy programs use is a few percent of cooling cost per degree of setback, but treat that as an estimate. To see what cooling costs you, use the cost to run an air conditioner calculator.
Humidity: the setting that changes how 78 °F feels
At 78 °F and 40% RH most people feel comfortable; at 78 °F and 65% RH the same room feels sticky. Sweat evaporates slowly in humid air, so you feel warmer. Keeping indoor humidity around 40 to 50% often lets you set the thermostat 2 or 3 °F higher with no loss of comfort.
- Set the thermostat fan to Auto so moisture on the coil is not blown back into the house.
- If your system has a dehumidify or humidity setting, use it.
- Check RH with a hygrometer; if it stays above 55 to 60%, see does AC remove humidity and AC not removing humidity.
The dew point calculator gives a single number for how humid the air really is.
Sleeping temperature
Body temperature naturally drops at night, and a cool room helps. Sleep researchers often suggest a bedroom in the mid-60s °F, but in summer few people want to pay to hold that. A practical approach:
- Set the bedroom between about 70 and 75 °F.
- Run a ceiling fan on its summer (counterclockwise) setting; moving air makes the room feel roughly 3 to 4 °F cooler. See ceiling fan direction.
- Use lighter bedding and breathable sheets.
- Program the thermostat to start cooling 30 to 60 minutes before bedtime.
Setbacks without the heat-soak penalty
Raising the thermostat while you are out saves energy, but a very large setback on a hot day lets heat soak into walls, floors and furniture. The AC then needs hours to pull it back out. In hot climates, a setback of about 4 to 7 °F is usually a good compromise, timed to start recovery an hour or so before you get home. A smart or learning thermostat can calculate the start time automatically. See how long it takes to cool a house.
Setting the thermostat to 65 °F does not make the house cool faster. A standard AC has one output; a lower setting only makes it run longer and overshoot.
When the house will not reach your setting
If the AC runs constantly and the house stays several degrees above the setting on an ordinary summer day, check the simple things first: a clogged filter, closed supply or return grilles, a dirty outdoor coil, or a thermostat in direct sun. Our guide to thermostat not reaching temperature walks through the full checklist. Supply air should typically be about 15 to 20 °F cooler than return air; the AC vent temperature page explains how to measure it.
Thermostat location and settings that matter
A thermostat measures the temperature where it sits. If it is on a wall that gets afternoon sun, near a lamp or kitchen, or above a supply register, it reads warm and runs the AC longer than needed. On an exterior wall or near a drafty door it can read cool and leave the rest of the house warm. Interior walls about 5 feet up, away from heat sources, give the most representative reading.
Check two settings in the thermostat menu. The fan should normally be set to Auto. The cycle rate or swing setting controls how far the temperature drifts before the system starts again; a very tight setting causes short cycles, while a wider one gives longer, more efficient runs with slightly bigger temperature swings. If your thermostat has an option for a heat pump or a multi-stage system, make sure it matches the equipment; the thermostat wiring guide covers the terminals.
Frequently asked questions
Is 72 °F too cold for an AC setting?
Not harmful, just more expensive. Holding 72 °F instead of 78 °F means more run time and higher bills, and in very hot weather some systems cannot hold it.
What temperature should I set my AC when I'm on vacation?
About 85 °F works for most homes. Avoid turning the AC off entirely in humid climates, since indoor humidity can climb high enough to encourage mold.
Is it cheaper to leave the AC on all day?
A moderate setback while you are out usually saves energy. Turning it fully off on very hot days can lead to long recovery times and high humidity, which reduces or cancels the savings.
What is the most comfortable AC temperature?
For most people, about 74 to 78 °F with indoor humidity between 40 and 50%.
Last reviewed 2026-10-28