Best for: Settling the argument with your spouse about whether it’s worth raising the temperature when nobody’s home.
Everyone has a theory about air conditioning. Most of them are wrong.
One person swears that keeping the house at a constant temperature saves money because the AC doesn’t have to “work as hard” to cool the house back down. The other person insists that raising the temperature when you’re not home obviously saves money because the AC runs less.
They’re both partially right, but one side has physics on their side.
Let’s settle this with math.
The Physics (Simplified)
Your home constantly gains heat from the outside in summer. The bigger the temperature difference between inside and outside, the faster this happens.
This is called heat transfer, and it’s governed by basic thermodynamics. When your house is 72 degrees and it’s 95 degrees outside, heat infiltrates through your walls, windows, and roof. The bigger the temperature gap, the faster you gain heat.
Keeping the house at 72 degrees all day:
Your AC runs frequently to remove the heat constantly infiltrating. The heat gain is continuous because the temperature difference is continuous.
Raising the temperature to 82 degrees when you’re gone:
The house warms up. The temperature difference between inside and outside shrinks. Heat infiltration slows down. Your AC runs less.
Yes, when you return home and lower the thermostat back to 72 degrees, the AC has to run to cool the house back down. But the energy used to cool the house is less than the energy saved during the hours when the temperature was higher and heat gain was slower.
The Numbers
Let’s use a real example. Assume:
– 1,500 sq ft house in Texas or another hot climate
– Summer cooling costs with central AC
– Outdoor temperature: 95 degrees
– Normal indoor temperature: 72 degrees
– Setback temperature: 82 degrees
– You’re gone 8 hours a day (work, errands, etc.)
Scenario 1: Constant 72 Degrees
Your AC maintains a 23-degree temperature difference between inside and outside for 24 hours. Average summer cooling bill: $200/month.
Scenario 2: 82 Degrees for 8 Hours, 72 Degrees for 16 Hours
Your AC maintains a 13-degree difference for 8 hours and a 23-degree difference for 16 hours. The reduced heat gain during those 8 hours lowers your overall energy use.
Average summer cooling bill: $160/month.
Savings: $40/month, or $160 over a typical cooling season.
The exact savings depend on your home’s insulation, outdoor temperature, and how long you set back the temperature. But in almost every scenario, turning up the thermostat when you’re not home saves money.
In hot, humid climates like Houston or Florida, the savings can be even higher because your AC works harder to remove both heat and humidity.
What About “Working Harder” to Cool the House Back Down?
This is the most common misconception. People think the AC uses extra energy to bring the temperature back down, negating the savings.
It doesn’t work that way.
The amount of energy needed to lower the temperature from 82 to 72 degrees is less than the energy saved by not maintaining 72 degrees for those 8 hours.
Think of it this way: if you raise the thermostat (letting the house get warmer), your house gains less heat from the outside because the temperature difference is smaller. When you lower it back down, you’re just removing the heat that infiltrated. You’re not using “extra” energy. You’re using less energy overall because less heat infiltrated in the first place.
The 8-10 Degree Setback Rule
Most experts recommend raising your thermostat 8-10 degrees when you’re away. Going from 72 to 80-82 degrees provides meaningful savings without making your AC system work inefficiently.
Some studies suggest you save about 1% on your cooling costs for every degree you raise the thermostat over an 8-hour period. An 8-10 degree increase for 8 hours a day could save you roughly 8-10% on your bill.
If your summer cooling bill is $200/month, that’s $16-20/month, or $65-80 over a typical cooling season. In extreme climates like Phoenix or Houston where you run AC 6-7 months a year, you could save $100-140 annually.
Humidity: The Complicating Factor
In humid climates, air conditioning does two jobs: it cools the air and removes moisture. When you let your house warm up during the day, humidity can creep up too.
If you let the house get too warm and humid, your AC will have to work extra hard to dehumidify when you return. This is where the “working harder” argument has some validity, but only in very humid climates and only if you raise the temperature too much.
For humid climates:
– Raise the thermostat by 8 degrees instead of 10-12 degrees
– Don’t let indoor temperature exceed 80-82 degrees to avoid excessive humidity buildup
– Consider a dehumidifier if your AC struggles to keep humidity under control
In dry climates (Phoenix, Las Vegas, Denver), humidity isn’t a factor. You can raise the temperature more without worry.
What About Heat Pumps?
Heat pumps work as both heaters and air conditioners. In cooling mode, they’re just regular AC units, so everything above applies.
Unlike heating mode (where heat pumps can struggle with large temperature swings), heat pumps have no problem when you raise the temperature in cooling mode. Set it higher when you leave. No special considerations needed.
What If You Work From Home?
If you’re home all day, there’s no point in raising the temperature. You’d just be uncomfortable.
But you can still save money:
– Set the thermostat 2-3 degrees higher and use fans to stay comfortable
– Use a portable AC or window unit in the room you’re in instead of cooling the whole house
– Close vents in unused rooms to concentrate cooling where you need it
– Block direct sunlight with blinds or curtains during the hottest parts of the day
Even raising the temperature by 2-3 degrees saves 2-3% on your bill, which adds up over time.
Ceiling fans make a room feel 3-4 degrees cooler without actually lowering the temperature. Run fans in occupied rooms and you can keep the thermostat higher.
Programmable and Smart Thermostats
This is where technology actually helps.
A programmable thermostat lets you set a schedule: higher temperature during work hours, comfortable temperature when you’re home, slightly higher when you’re asleep.
A smart thermostat (Nest, Ecobee, Honeywell) does the same thing but learns your schedule, adjusts automatically, and can be controlled remotely.
The upfront cost is $50-250 depending on the model, but the energy savings usually pay for the thermostat within 1-2 years.
If you’re still manually adjusting your thermostat every day, you’re working harder than you need to. Set it once and forget it.
The Overnight Question
Should you raise the temperature at night?
This depends on personal preference more than heating does.
Some people sleep fine in a warmer house (75-78 degrees). If you’re comfortable sleeping warmer, raising the temperature at night saves energy.
But most people struggle to sleep when it’s too hot. Sleep quality matters more than a few dollars on your electric bill. If you need the house at 70 degrees to sleep well, keep it there.
One compromise: use a bedroom-only window unit or portable AC and let the rest of the house warm up overnight. You stay cool, but you’re not air conditioning empty rooms.
Common Objections (And Why They’re Wrong)
“My house takes forever to cool back down.”
That’s an insulation problem, not a thermostat problem. If your house gains heat quickly, you need better insulation, window treatments, and air sealing. But even with poor insulation, setting back the temperature still saves money.
“The AC runs constantly when it’s trying to catch up.”
Yes, but it runs less overall. The total runtime is still lower than maintaining a constant temperature all day.
“I don’t want to come home to a hot house.”
Program the thermostat to start cooling the house 30-60 minutes before you get home. Problem solved.
Many smart thermostats have geofencing that detects when you’re heading home and starts cooling automatically.
“It’s bad for the AC system.”
No, it’s not. AC systems are designed to cycle on and off. Running less frequently actually extends the lifespan of the equipment.
“The humidity gets unbearable.”
Only in very humid climates when you raise the temperature too much. Keep the increase to 8 degrees and indoor temperature below 82 degrees, and humidity won’t be a problem.
What About Pets?
If you have pets at home, you can’t let the house get too hot.
Dogs and cats handle heat differently. Dogs overheat faster, especially larger breeds and breeds with thick coats. Cats tolerate heat better but still have limits.
Safe temperature ranges for pets:
– Dogs: Keep the house below 80-82 degrees
– Cats: Can handle up to 85-90 degrees, but 80-82 is safer
– Elderly or sick animals: Keep it cooler, around 75-78 degrees
If you’re leaving pets home alone, raising the temperature 8 degrees (72 to 80 degrees) is usually fine. Anything more risks their health.
Make sure they have plenty of water, access to cool tile floors, and shaded areas.
The Bottom Line
Raising your thermostat when you’re not home always saves money. The physics are clear: the less you cool your home, the less energy you use.
The amount you save depends on:
– How long you’re gone
– How much you raise the temperature
– Your local climate and humidity
– How well your home is insulated
Here’s what to do:
– Raise the temperature 8-10 degrees when you’re gone for 8+ hours
– Use 8 degrees in humid climates to avoid excessive humidity buildup
– Keep the house below 82 degrees if you have pets
– Raise the temperature 2-3 degrees at night if you can sleep comfortably warmer
– Buy a programmable or smart thermostat if you don’t have one
– Fix insulation and air leaks if your house can’t hold temperature
– Use ceiling fans to feel cooler without lowering the thermostat
The “constant temperature” theory sounds logical but it’s wrong. You’re not saving money. You’re just wasting energy to keep an empty house comfortable.
Raise the thermostat. Your AC will be fine. Your wallet will thank you.
Summer-Specific Tips to Maximize Savings
Beyond the thermostat, here are other ways to reduce cooling costs:
Block the sun:
– Close blinds and curtains during the hottest part of the day (2 PM – 6 PM)
– Consider blackout curtains or reflective window film for west-facing windows
– Plant shade trees on the south and west sides of your house (long-term solution)
Reduce internal heat gain:
– Don’t use the oven during the hottest part of the day (grill outside or use the microwave instead)
– Run the dishwasher and dryer at night or early morning
– Turn off lights in empty rooms (incandescent bulbs generate significant heat)
– Unplug electronics that generate heat when not in use
Improve airflow:
– Use ceiling fans (counterclockwise in summer to push air down)
– Keep vents unblocked by furniture or curtains
– Change AC filters monthly during heavy use
– Have your AC serviced annually to maintain efficiency
Seal air leaks:
– Check weatherstripping around doors and windows
– Seal gaps around pipes, vents, and electrical outlets
– Make sure attic insulation is adequate (R-30 to R-60 depending on climate)
These changes compound with thermostat setbacks to maximize savings.
The single most effective thing you can do is turn up the thermostat when you’re not home. Everything else is supplementary.