Should You Leave Air Conditioner On All Day?

It's one of the most common AC debates: is it cheaper to leave the AC running all day at a moderate temperature, or turn it off when you leave and blast it when you get home? The answer depends on your situation — but the science is clear.

The Short Answer

No — for most homes, turning the AC off (or raising the setpoint significantly) when you're away saves money. But "turning it off" doesn't mean switching it off completely. It means raising the temperature to 85°F (29°C) while you're out, not letting the house bake at 95°F+.

The Argument for Leaving It On

Some people believe it takes more energy to cool a hot house back down than to maintain a cool temperature all day. This is a myth for most situations. Here's why:

• The rate of heat gain in a house is proportional to the temperature difference between inside and outside. A cooler house gains heat faster than a warmer one.
• Keeping the house at 72°F all day means the AC is constantly fighting a large temperature differential with the hot outside air.
• Letting the house warm to 85°F while you're away reduces that differential, so less heat enters — and the AC does less total work.

When Leaving It On Makes Sense

There are situations where running the AC continuously is justified:

• Pets at home: Dogs and cats can't tolerate extreme heat. If pets are home, keep the AC running at a pet-safe temperature (around 78°F / 26°C).
• High humidity climates: In very humid regions, turning off the AC can allow humidity to spike, leading to mold growth, wood warping, and damage to electronics. Running the AC in dry mode or at a higher setpoint maintains humidity control.
• Short absences: If you're only out for 1–2 hours, the energy savings from raising the temperature may not offset the cost of cooling back down quickly.
• Extreme outdoor heat (110°F+): In extreme heat, a house can heat up so rapidly that the AC struggles to recover. In these conditions, maintaining a moderate temperature all day may be more efficient.

The Most Efficient Approach: Smart Scheduling

The best strategy is neither "always on" nor "always off" — it's scheduled cooling:

1. Raise the temperature to 85°F when you leave
2. Schedule the AC to start cooling 30–45 minutes before you return
3. Come home to a comfortable temperature without having cooled an empty house all day

The easiest way to do this is with a smart plug or smart thermostat:

• The GHome Smart Plug lets you set a daily schedule via app — turn off when you leave, turn on 30 minutes before you return.
• The Govee Smart Plug with Energy Monitoring shows you exactly how much electricity you're saving with the new schedule.
• A smart thermostat like the ecobee handles this automatically with geofencing — it detects when you leave and return and adjusts the temperature accordingly.

How Much Can You Save?

The U.S. Department of Energy estimates that raising your thermostat by 7–10°F for 8 hours a day (while at work) can save up to 10% per year on cooling costs. For a typical household spending $300–$500 on summer cooling, that's $30–$50 in savings — just from adjusting the schedule.

Summary

The bottom line: don't leave the AC running at full cool all day in an empty house. Raise the temperature when you leave, schedule it to cool before you return, and you'll save money without sacrificing comfort.