7 min readGrowing up in North Georgia, there was one thing my family never skimped on: air conditioning. My dad has owned and operated a local HVAC company for nearly four decades, and as a licensed technician, he made sure our house stayed refreshingly cool—sometimes even colder than I preferred. Still, during those brutally hot summers, it was hard to argue with his approach.
Even though central air conditioning has been common in American homes for decades, most people know surprisingly little about how it actually works. For many homeowners, it's easy to forget about the system until it stops working, needs to be replaced, or causes utility bills to spike. That's often when myths start to spread. Countless people have grown up believing well-meaning but inaccurate advice about air conditioning, much of it passed down in the name of saving money on energy costs. Unfortunately, many of those tips are outdated—or simply false.
To separate fact from fiction, I asked experts to weigh in on some of the most common air conditioning myths. Keep reading as we debunk the biggest misconceptions you may have been taught about AC.
Lie: It’s Better to Run the Air Conditioning Only at Night
In many parts of the world where temperatures regularly soar, air conditioning is often used sparingly to reduce energy costs. Many households limit AC use to nighttime or only during the hottest parts of the day, believing it's the most efficient way to stay comfortable while keeping utility bills in check.
Truth: It does cost more to run your air conditioning than it does a fan. You pay the utility company for the amperage you use, and an air conditioner draws more amps than a fan does. But that doesn’t mean it’s better to do this. Your air conditioner has to work harder to cool the house when you let the temperature go to extremes.
“If you let your house get hot, everything in it gets hot, even the chairs,” says David Moody of Moody Heating & Air Conditioning. It takes longer to cool all those things down. That can also cause wear and tear to happen more quickly—and replacing an air conditioner is pretty expensive.
Big swings in temperature from hot to cold aren’t great for anything you own—including other appliances, like your fridge, and the structure of your house itself, which is affected by humidity. Moody recommends not letting your home get hotter than 80 degrees Fahrenheit.
Lie: The AC Won’t Help the Humidity
In humid climates, some people believe running the air conditioner isn't worth it because the air will still feel damp regardless. As a result, many households use their AC less often under the assumption that it won't make much of a difference in overall comfort.
Truth: “Air conditioning is actually all about dehumidification,” Moody says. That’s how it works, by pulling the warm moisture out of the air, cooling that air, and then pushing it back out into your house. The condensation that accumulates from this process typically drains into an outgoing pipe or a pan, which is why leaks in attics are more common when it’s super hot outside—more condensation is building up and can overflow. It’s important to get your system checked for clogs in the spring to ensure the water can drain out.
Lie: Air Conditioning Will Make You Sick
There are lots of variations on this one: Going from hot air to cold air is bad for you. Or, it’s bad to sleep near the draft from an air-conditioning vent.
Truth: The draft itself isn’t going to make most people sick—although Moody wouldn’t recommend positioning a baby’s crib right under an air conditioning return. “Clean drains and clean filters are a must,” he says. “This applies to most everything in life. If everything is clean, health should not be an issue.”
He recommends changing your air conditioning filters once a month all year and being especially vigilant about it in the spring and summer when allergens and temperatures peak or if you have pets that shed a lot. In his opinion, there’s no need for most people to buy special and expensive HEPA or similar filters—the most important thing is changing them regularly.
Lie: The Lower the Thermostat, the Faster It'll Cool Down
You might have heard your parents arguing about this one—for instance, if your dad felt hot and cranked the dial down to 60 instead of the 70 your mom preferred.
Truth: “Turning down the temperature from, say, 70 to 60 when it’s 80 degrees in the house will not help it cool down faster,” Moody says. The only exception might be if your system has a two-stage or variable-speed compressor—and you’ll likely crank up your energy costs since it takes more BTUs to get that going.
Lie: Live by the 20-Degree Rule
You may have grown up hearing some version of this household mandate: The thermostat should never be set to a temperature more than 20 degrees hotter or colder than the outside temperature.
Truth: “I never heard of that one,” Moody says. Still, he says, it’s the temperature inside your house that matters, not outside. “A typical air-conditioning system will change the intake temperature”—aka the temperature of the air it’s pulling in from the rooms in your house—“by 20 degrees,” he adds. If you don’t run the air consistently, it’s actually pretty easy for it to get hotter inside than it is outside.
Lie: Turn Off the AC When You Go Out of Town
This money-saving move appears on many a family’s vacation prep list, along with unplugging the TV and turning off the water supply.
Truth: “We don’t recommend turning the AC off,” Moody says. “Quickly accumulating a lot of humidity isn’t good for a house.” As a family with indoor dogs and cats, we’d personally never do this. Pets need to stay cool too. (My parents also leave on Animal Planet for their dogs, but that’s strictly optional.) It also goes without saying that you should never leave a pet in a hot house, car, or yard.
What you can do if you want to reduce your electric usage while you’re away is turn the thermostat up to 78 degrees, Moody suggests. That’s enough to keep the humidity in control and the house relatively comfortable.
Lie: You Should Close the AC Vents in an Empty Room
You might’ve seen your mom or dad use the little dial on the register in the guest room to close it as soon as your aunt or grandma went home from a visit, the idea being that it would keep overall costs down and/or make other rooms cool faster.
Truth: “Closing vents is not good for an AC system,” Moody says. “If it has been installed properly, the air is sized accordingly for the entire house.” A closed vent can throw off the balance. You also don’t want to close the door and let humidity build up in just one room. It’s bad for paint, furniture, windows—you name it.
Lie: A Ceiling Fan Is Just as Good as AC
This one is for all the New Englanders who grew up without central air.
Truth: It’s objectively false to say a fan does the same thing as air conditioning. It simply does not. “Having the fan on only helps move the air around,” Moody explains. “It has nothing to do with dehumidification, so it’s no help with cooling or humidity.”
What a ceiling fan can do is help distribute cold air. Pro tip: In the summer, set your ceiling fan to reverse so it runs counterclockwise. (You may not have noticed before, but most ceiling fans have this feature.) “Cool air molecules are heavier than hot ones, so running your ceiling fan counterclockwise will help move some of the cool air around the room.”
Lie: You Don’t Need AC If You Have a Cross Breeze
In homes that get plenty of natural airflow, many people assume opening a few windows is enough to stay cool. While a cross breeze can certainly make a space feel more comfortable on mild days, it's often believed to be a complete substitute for air conditioning—even during periods of intense heat.
Truth: This one is a partial truth that depends on your tolerance for heat and humidity. Homes and apartment buildings built before air conditioning (or even electricity) were designed to help them stay cool in the summer and warm in the winter. Windows were sized and positioned strategically to allow cross breezes to flow through. Moving air helps dissipate humidity and feels nicer than hot, stagnant air. If you live near water, the breeze may be cool too. Moody points out that transom windows served a similar purpose. “They’re actually an old-school way to try to cool houses and buildings,” he says. “Hot air rises, and any cross ventilation pushes the hot air from front to back.”
But there’s only so much a cross breeze can do, and the heat simply wasn’t as extreme or extended back then as it is now. Modern weather patterns make air conditioning essential now, especially in many urban environments.
Lie: You Should Never Use Your Stove During a Heat Wave
It’s the best excuse to order takeout—turning on the stove will make it even hotter in the house—but is there anything to it? How much can turning on one burner really affect the overall temperature?
Truth: Generally, and this depends on the exact stove you have and the burner you might use, but “one stove burner of heat is roughly equal to one ton of AC cooling: 12,000 BTUs,” Moody says. “So cook quickly or little to none on very hot days.” (The exception is an induction stove, which heats only the pot you’re cooking in, not the surrounding air.) You could also opt to do as he does and take some burgers or steaks out to the grill and hang out with the dog while you do your cooking there.
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