Let’s settle the heated debate over your AC, once and for all.
Jul 3, 2024, 8:00 PM UTC
Setting your thermostat just a single digit higher can help you save 6 percent on your cooling costs, according to the EPA. Getty Images
The Vox guide to extreme heatAdam Clark Estes is a senior technology correspondent at Vox. He’s spent 15 years covering the intersection of technology, culture, and politics at places like Gizmodo, Vice, and the Atlantic.
Micah Pollak had no idea the trouble he was getting himself into when he shared his preferred thermostat settings on social media. “I just discovered most of our friends set their AC at 68-73F during the summer,” Micah, who is an economist at Indiana University, posted on Threads in late June. “We keep ours at 77-78F. Are we monsters!?” Nearly a thousand replies later, the consensus was that, yes, Micah’s family are monsters, probably some type of lizard.
Although he didn’t realize it, Micah has been following a set of numbers from the Environmental Protection Agency that tends to spark an internet freakout every summer, often after a local news station does a segment on how to reduce your energy consumption and lower your utility bills. The recommendations include keeping your thermostat at 78º when you’re at home during the day, 82º at night, and 85º when you’re away during the warm months.
To many people, sleeping in 82º heat is simply outrageous. (Not to mention terrible for your sleep, according to experts.) But energy prices are crazy too, and they’re only expected to rise as utility companies spend more and more to make the grid more resilient to the effects of climate change. Extreme weather events are becoming more common, and heat waves in particular can strain the power grid, especially when thousands of people are running their ACs at full tilt.
So maybe cranking up your thermostat isn’t such a bad deal. Typically, I’m inclined to set my AC to 72 on a really hot day. If I could get used to a balmy 78º inside, I’d not only save money, I’d be doing my part to keep the grid running smoothly so that everyone can enjoy a little bit of air conditioning, too. And the savings are real. The EPA says that for every degree warmer you set your AC, you can save 6 percent on your cooling costs, although you get diminishing returns as you go higher and higher. Put simply, if your cooling bill is usually $170, setting your thermostat a single digit higher will save you over $10 a month.
There’s one big problem, though. That 78º baseline isn’t a real federal government recommendation. The EPA’s Energy Star program does have a guide for programmable thermostat settings, but it doesn’t recommend a specific number to set your thermostat to in the summer. The numbers that show up in the news actually come from a table in a 2009 document that offered examples of what energy-saving settings could look like.
“Your household temperatures are very much a personal choice, and ultimately people should do what makes them comfortable,” Leslie Jones, a public affairs specialist from Energy Star, told me.
The agency’s official position is that you can save “up to 10 percent on heating and cooling settings by simply turning your thermostat 7°-10°F for 8 hours a day from its normal setting.” In other words, if you keep it at 71 while you’re home, go ahead and set it to 78 if you leave for the day.
Then again, setting your thermostat at 78º at all times is not a monstrous idea. And setting it at 72º probably means you’re wasting some energy.
Nobody wants the government telling them to suffer more in the summer heat. A lot of our assumptions, though, about how air conditioning works, how to optimize the effectiveness of this century-old technology, and how to save energy in the process are just that: assumptions. To clear up the outrage over where we set out thermostats, I talked to experts in thermal comfort, HVAC technology, and the built environment.
It turns out, some of the most effective ways to stay cool are both simple and cheap.
It’s a time-honored American tradition to fight over the thermostat. Winter, summer, spring, and fall, any given home will be too hot or too cold for someone in the family.
This is for good reason, too. Physiologically, we each have our own optimal thermal comfort level. It comes down to a few key factors, according to Boris Kingma, a human thermal performance researcher at the Netherlands Institute of Applied Technology (TNO). The environment, including temperature, humidity, wind, and solar radiation, is obviously the big one. If it’s hot outside, you’ll feel hot. But a person’s metabolic rate and general physiology, including age and overall health, also play a big role — as does the clothing you’re wearing.
Metabolism is what’s at play when you talk to people who say they “run hot.” They might literally do that if they have a high metabolism, which causes your body to produce more heat. People with more muscle mass, for instance, tend to have higher metabolisms, retain heat, and prefer cooler temperatures. The opposite goes for people with lower metabolisms, who lose heat and might need to wear a sweater in their over-air-conditioned office. Our metabolisms decrease with age, which might be why you think your grandparents keep their house too warm.
It is therefore difficult, if not impossible, to find a single thermostat setting that will make all of America happy. Heck, it’s hard enough to agree on anything in a single family. But the good news is that our bodies are very good at acclimating to new environments. Kingma told me that it only takes about 14 days for your body to adjust to a new baseline temperature. So if you’re used to New York City’s relatively mild summer average of 80°F and then move to Miami, where it’s closer to 90°, you’ll probably get used to it.
The same holds for thermostat settings. If you do try and save some money by moving your thermostat one digit up, your body will adjust in a couple weeks, especially if you use a fan and wear lightweight clothing inside. Fans are especially effective, since they move air around your skin, helping sweat evaporate. Loose clothing has the same effect.
“Many of the solutions to this particular problem don’t need to be high tech,” said Kingma. “Dealing with temperature is about as old as humans.”
The role of evaporation cannot be overstated here. Sweating cools us down because the fluid on our skin evaporates and helps us shed heat. This explains why humidity is so miserable: The air is already so saturated with moisture that your sweat doesn’t evaporate effectively, which means you don’t cool down as easily. On windy days or in dry climates — a dry heat, if you will — sweat evaporates more readily, making it easier to stay cool. Fans can help in either scenario.
Focusing on reducing humidity is actually how we got air conditioning in the first place. In 1902, an engineer named Willis Carrier installed an “apparatus for treating air” at a printing company in Brooklyn that was having problems with magazine pages wrinkling in the summer heat. The machine sent air through coils filled with cold water, which removed humidity from the air and cooled the room. It wasn’t until 1922 that the Carrier Air Conditioning Company of America introduced the first practical centrifugal refrigeration compressor that would become the foundation for modern air conditioners.
Most AC units today do the job with three simple steps. They pull warm air out of the room, cool it down by running it over coils filled with refrigerants, and then pump the cold air back into the room while releasing the heat to the outside world by using a compressor, which is why your AC can sound like a starting car. Heat pumps, which can heat and cool a home, operate using the same principles when cooling — more on that in a minute.
Air conditioning is an energy-intensive process, and the refrigerants used in them present a few problems of their own. The most common refrigerants needed to make these machines work include chlorofluorocarbons (CFCs) and hydrofluorocarbons (HCFCs), commonly known as “freon,” which are greenhouse gasses that deplete the ozone and contribute to climate change. The EPA has been banning many of these chemicals in recent decades to comply with the Montreal Protocol on Substances Depleting the Ozone Layer. However, many modern replacements that do not damage the ozone are still potent greenhouse gasses.
In other words, air conditioning has historically been great for comfort but bad for the climate.
Not only do they require a lot of energy, which may or may not be supplied by fossil fuels, but most air conditioners also pump more greenhouse gasses into the atmosphere. ACs can keep us cool, but they’ll also warm the planet in the process. It’s a real paradox.
Technologies like heat pumps promise a greener future for heating and cooling, but it will take years to update our HVAC infrastructure due to the cost and sheer scale of trading old, inefficient equipment with new systems. And for many, including renters and certain businesses, those upgrades may even be impossible. So for now, the fight over the thermostat continues.
There is no magical thermostat number to make everyone happy and maximize energy savings. For some, like Micah, the economist, 78º during the day is just fine. For others, 68º is perfect. There have been attempts to solve this problem on an institutional level. And if you’ve ever spent a hot summer day in a large office building, you know that some of those attempts have failed.
The big difference between setting a thermostat at work and at home, of course, is that you typically don’t have any control over the office thermostat. A look at how offices attempt to make everyone comfortable does, however, provide some insight into how we make decisions at home.
First formed as the American Society of Heating, Refrigeration, and Air-Conditioning Engineers, ASHRAE sets the industry standards for all things HVAC-related. One specific standard, ANSI/ASHRAE Standard 55, provides guidance on how to optimize thermal comfort in the built environment. That includes adapting temperature, humidity, air movement, and thermal radiation in an occupied space to the activity and clothing of the people occupying it. If you’re building a business and want to figure out how to make everyone inside the office comfortable, this is the guide.
ASHRAE, unlike the EPA, specifies an ideal number to set a building’s thermostat to. It’s a range, actually: around 23°-26°C, or 73.4°-78.8°F, in the summer. According to Bjarne Olesen, a former ASHRAE president, “At least 80 percent of men and women are satisfied in that range.” Some might say that the upper end of that range is a bit too warm for good productivity. That assumption would line up with a 2021 review of scientific studies about temperature and work performance, which found the optimal temperature is between 22°-24°C, or 71.6°-75.2°F. But again, the number on the thermostat is not the only thing to consider.
Even fancy office buildings are not immune to energy costs. While the EPA suggests that a single digit, or setpoint, higher on the thermostat can add up to 6 percent savings on your cooling bill, the savings are magnified if you scale them up to an entire building or even an entire city. A 2023 study of three decades of weather and energy cost data concluded that a single setpoint change coupled with behavioral changes could result in 20 percent energy savings. Behavioral changes, which include everything from using fans in addition to AC and wearing lighter clothing, are especially essential in cities, which are designed to depend on air conditioning.
“The technology of cool air allowed people to design buildings that would not normally be comfortable in our environment,” said Robert Bean, a fellow and lecturer at ASHRAE. “And as this environment changes, it puts us in a tough spot.”
There have been some high-profile experiments in thermostat tweaks and energy savings. In 2005, Yuriko Koike, who was Japan’s environment minister at the time, launched an initiative called Cool Biz that pushed government offices to turn their thermostats up to 82ºF from May to September to save energy and reduce greenhouse gas emissions. As an incentive of sorts, workers were allowed to ditch their formal office attire — suits and ties, for instance — in favor of lighter, more casual attire, like aloha shirts and linen pants. There were fashion shows and everything. Big corporations followed the government’s lead, and within a couple years, Cool Biz was a national pastime. By 2023, some 86 percent of workplaces participated in the initiative.
When it comes to energy savings, turning the thermostat up works, too. Estimates vary, but Cool Biz reportedly saves Japan between 1 and 3 million tons of carbon dioxide emissions every year. The program became even more significant in the aftermath of the 2011 Fukushima nuclear disaster, when reactors across the country shut down and the government mandated further energy savings. They called it Super Cool Biz. There’s even an initiative to turn thermostats down during the winter months. And yes, it is called Warm Biz.
“It’s not rocket science,” said Kingma, the Dutch researcher. “As long as you have the ability to adapt, the problem may be solved by actually adapting.”
Not everybody in Japan loves this, of course. And there is research that shows productivity starts to dip once the temperature rises to 77°F. But Japan’s example shows that an entire nation can adapt to different indoor temperatures for the greater good — and they can look good while they do it. Maybe the rest of the world can, too.
Let me make a confession: I like the thermostat set at 72. If it’s 72 or less outside, I’ll open a window and enjoy the breeze. If it’s warmer, I seal myself into my Brooklyn apartment, let the AC do the work, and wait for nightfall.
Or at least, that’s what I used to do. I actually stopped setting my thermostat at 72 while reporting this story. After my conversations with thermal comfort researchers and HVAC professionals, I realized that cranking up the AC unnecessarily isn’t just a waste of energy, it’s not that comfortable either. It’s silly to get goosebumps inside in the middle of a July day because your cooling machine has cooled the room down too much. That’s why I started to heed the advice of the experts. And let me tell you, these experts are fans of fans.
Stefano Schiavon, a professor at the University of California Berkeley and a member of ASHRAE, told me his colleagues stick with a “fans first” strategy to cooling. “If you feel hot,” he said, “the first thing you turn on is a fan.” You can also use fans to supplement your AC, especially if you’re trying to stay comfortable at a high setpoint. Wearing loose clothing will only add to the cool enjoyment of it all.
“There’s been a movement — arguably driven by the air conditioning industry — to say the fan is a technology of the past, we don’t want them,” Schiavon explained. “But fans cost much less to manufacture, they use a small fraction of the energy, and they’re very intuitive to people so people know how to use them.”
There are also less obvious strategies to stay cool and save energy. Running your dishwasher and doing laundry at night cuts down on bringing excess heat into the home. You can also try spending time in the rooms of your house or apartment furthest from the sun, like on the northern side of the building or in a basement.
Maintenance also plays a big role in making sure everything is running at peak efficiency. That means cleaning your air conditioner vents and changing filters regularly. You should also be sure to keep cool air in and hot air out, so be careful about opening windows and doors unless you’re doing so to ventilate the space.
Smart thermostats are another promising solution, although they don’t necessarily work in older homes with radiators or window units. If you have central AC, you can swap out the thermostat on your wall with an internet-connected thermostat that lets you control everything with an app. You set the system up to automatically change settings at certain times of day or optimize their performance to save energy. Good ones cost about $250, but Amazon sells a basic one for $80. If you have a window unit, you can upgrade it with a smart AC controller that adds connectivity. Your utility company may even help you pay for one of these devices.
You also shouldn’t sleep on the heat pump trend. Again, heat pumps operate on the same principle as an air conditioner for cooling: They use electricity and refrigerants to pull humidity and heat out of the air. They tend to be as efficient as ACs, too, so don’t expect your summer bills to drop if you make the switch. But by moving heat from one place to another rather than actually generating it, heat pumps are much more efficient when it comes to heating buildings. The Department of Energy says that heat pumps use up to 65 percent less electricity than old fashioned furnaces or baseboard heaters. You can also get a tax break for installing one in your home.
“There’s no wrong way to save energy,” said Jones from Energy Star. “It’s just a matter of figuring out what is appropriate and right for you given your situation.”
It’s possible that some magical new invention could come along and change the way we stay cool. One promising technology involves installing radiant panels filled with cold water that effectively pull heat off of people as they pass by them without actually cooling the air. Researchers at Princeton showed off a system like this in Singapore in 2019. They called it a Cold Tube, and people who walked through it reported feeling cool, even though the temperature of the air didn’t actually change. This type of technology is decades away from becoming mainstream, but it’s proof that a future without air conditioning is possible.
But for the futuristic AC-free technology to work well, guess what’s required? Fans.
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