Is It Cheaper to Leave AC on All Day or Turn It On and Off?

This question comes up every summer, and the answer matters because the difference can add up to a significant amount on your electricity bill. The short answer: for most households, turning the AC off or raising the temperature when you leave saves money. Here is the full explanation.

The Physics of Home Cooling

A home loses cool air to the outside at a rate proportional to the temperature difference between inside and outside. The cooler you keep the house, the faster it loses that coolness — and the harder the AC works to maintain it.

When you turn the AC off and let the house warm up while you are away, the rate of heat gain slows as the indoor temperature rises toward outdoor temperature. When you turn the AC back on, you pay a one-time cool-down cost. In most cases, this one-time cost is less than the continuous cost of maintaining a cool temperature in an empty house for 8 hours.

What the Research Shows

The US Department of Energy and most energy agencies consistently recommend turning the thermostat up (or the AC off) when leaving for more than an hour. Their guidance: raising the set temperature by 7°C to 8°C (about 10°F–15°F) for 8 hours a day can save approximately 10 percent on annual cooling costs.

Turn Off vs Raise Temperature: Which Is Better?

When Leaving It On All Day Makes Sense

• Pets at home that cannot tolerate heat — set to 26°C–28°C, not your personal comfort setting
• Extreme outdoor heat above 40°C (104°F) where the home heats up very rapidly
• Very high humidity climates where turning off allows moisture buildup and potential mold
• Short absences under 1 hour where the cool-down cost on return approaches the maintenance cost
• Heat-sensitive items like musical instruments, artwork, or electronics that should not be exposed to high temperatures

The Smartest Approach: Pre-Cool With a Timer

Rather than choosing between all-day on or all-day off, use a timer or smart plug to turn the AC on 30 minutes before you arrive home. You get a cool room on arrival without paying for 8 hours of cooling an empty house. This is the approach recommended by most energy efficiency experts.

👉 GHome Smart Plug – Works with Alexa and Google Home

Measure It for Your Specific Home

Home insulation, climate, AC size, and usage patterns all affect the answer. If you want a definitive answer for your situation, use an energy monitor to measure actual electricity use on an all-day-on day versus a turn-off-and-pre-cool day. The data will tell you exactly which approach costs less.

👉 PN2000 Plug-in Kilowatt Electricity Usage Monitor

Final Thoughts

For most households, turning the AC off or raising the set temperature significantly when leaving for more than an hour saves electricity compared to leaving it running all day. The best practical solution is a timer or smart plug that pre-cools the home 30 minutes before you return — giving you comfort on arrival without the cost of cooling an empty house.