Is It Cheaper to Leave the AC On or Turn It Off When You're Out?
Last updated: October 18, 2026 · 5 min read
Almost everyone has stood at the thermostat on the way out the door and wondered the same thing: is it smarter to leave it running so the house stays cool, or shut it off to save money while nobody is home? The instinct to switch it off is understandable — but the honest answer is a little more interesting than either extreme, especially in the Texas heat.
The short answer
The winner is usually neither extreme — it is a setback. Letting the temperature rise about 4-7°F while you are out for hours, then cooling back down when you return, generally uses less energy than holding a cold setpoint all day. But in a Texas summer, do not switch the AC fully off for long stretches — our humidity climbs and the system then has to remove heat and moisture on recovery. A setback beats off.
The Myth: Cooling a Hot House Back Down
The worry that keeps people from touching the thermostat goes like this: if I let the house get hot, the AC will have to work so hard to cool it back down that I will spend more than if I had just held it steady. It sounds reasonable, and for the most part it is simply not true. The physics runs the other way, and understanding why makes the right choice obvious.
Why a Setback Actually Saves Energy
Heat moves from hot to cold, and the bigger the temperature difference, the faster it moves. When you hold your house at a chilly setpoint on a 100-degree afternoon, you are maintaining a huge gap, and heat pours in through the walls, windows, and roof the entire time — so the AC keeps running to push it back out. Let the indoor temperature drift up a few degrees while you are away and that gap shrinks, so the house gains heat more slowly and the system runs far less. The energy you save during those hours comfortably outweighs the extra cooling it takes to bring the house back down when you return. That is why a setback of roughly 4 to 7 degrees during a workday nets out cheaper than holding cold all day, and it is exactly what the Department of Energy recommends. Because each of those saved kilowatt-hours is billed at your effective rate, the setback shows up directly on the bill.
The Texas exception: do not switch it fully off
A setback is not the same as OFF. In our humid summers, a house left with the AC completely off for a long stretch takes on moisture as well as heat, and the system then has to wring out both when you return — a slow, energy-hungry recovery, with mold and comfort suffering in the meantime. Raise the setpoint, do not kill the system.
What to Set It To for a Workday
For a normal day at work, aim for a setback of about 4 to 7 degrees above your usual comfort setting. If you keep the house around 76 when you are home, letting it drift to roughly 80 to 82 while everyone is out captures most of the available savings without letting humidity build up. The easiest way to get this right every day is to stop relying on memory: a programmable or smart thermostat raises the temperature after you leave and cools the house back down shortly before you return, so you walk into comfort and still bank the savings. Pair it with a sensible home setpoint from our guide on the best AC temperature for a Texas summer and the whole thing runs itself.
What to Do for a Multi-Day Trip
Leaving town changes the math a little. With nobody home for days, there is no reason to hold your everyday temperature — but there is still good reason not to switch the system off in a Texas summer. Set a higher hold, commonly in the mid-80s, so the AC still keeps humidity in check and protects your home and belongings while sipping far less energy than usual. You come back to a house that is warm but dry and quick to cool, instead of a muggy box that takes hours and a pile of kilowatt-hours to recover. It also keeps your cooling from being the runaway line on your bill, the way we describe in our look at what it costs to run AC in Texas.
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Is it cheaper to leave the AC on or turn it off?
For a normal workday, the cheapest option is usually neither extreme — it is a setback. Letting the thermostat rise several degrees while you are out, then cooling back down when you return, generally uses less energy than holding a cold setpoint all day. In a humid Texas summer, though, do not switch the system fully off for long stretches, because the house takes on moisture that the AC then has to work hard to remove on recovery.
Does it cost more to cool a hot house back down?
This is the common worry, and for the most part it is a myth. A warm house loses heat to the outdoors more slowly than a cold one, so while you are away the AC is not fighting to hold a big temperature gap. The energy saved during those hours of a higher setting more than covers the extra cooling needed to bring the house back down when you get home. The net result is lower usage, not higher.
What should I set the AC to when I'm at work?
A setback of about 4 to 7 degrees Fahrenheit above your normal comfort setting is the sweet spot for a workday. If you are comfortable at 76 when home, letting it drift to around 80 to 82 while the house is empty captures real savings without letting humidity get out of hand. A programmable or smart thermostat can raise it after you leave and cool the house shortly before you return.
Should I turn the AC off when I go on vacation?
For a multi-day trip you do not need to hold your everyday temperature, but do not switch it off entirely in a Texas summer. Set a higher hold — the mid-80s is a common choice — so the system still keeps humidity in check and protects the house, while using far less energy than normal. That beats returning to a hot, muggy home that takes hours and a lot of energy to recover.