Your Air Conditioner Is Lying to You

My electric bill last month was disgusting. I’ve kept my window air-conditioning units on for hours every day, and now I have to pay the price: the most expensive month of cooling that I’ve ever had. If there ever was a time to press my AC’s MONEY SAVER button, it would be now. But I don’t think I will, not this summer and not ever—because money-saver mode has always struck me as a sham.

In the murky world of home air-conditioning, “money saver” may go by different names. Some models have an ECO button, to signal that it’s more economically—or ecologically—sound. Others go with ENERGY SAVER . However it’s described, the benefit this setting claims to offer—a cheaper way to reach and hold your set-point temperature—seems too good to be true. If it were really possible to keep my living room at 72 degrees in money-saver mode, just like I do with normal cooling, then why should any other AC modes exist? (Wouldn’t they be a MONEY WASTER , by definition?) But if there is, in fact, some hidden trade-off here—if, for instance, using money-saver mode doesn’t really bring my living room all the way to 72 degrees, or keep it at that temperature—then the whole thing feels like misdirection. Why not just turn up the thermostat a few degrees myself? Wouldn’t that be like putting it in money-saver mode the old-fashioned way?

These were just my idle speculations, though, based on summers past. I had no idea how money-saver mode really worked. I had only my personal experience, on those days when I’d left my ACs on that setting by accident or aspiration, and made my family endure a trial afternoon of more “efficient” cooling. The outcomes of these experiments were never very good: By all accounts, rates of sweating and complaining in the home were markedly increased. With the MONEY SAVER button pressed, our living room felt somewhat HOTTER than we’d hoped—which made us CRANKY and UNCOMFORTABLE . So this summer, I set out to learn the secrets of the mode. What I’ve found has only made me more suspicious than I was before.

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Eco-friendly modes for air conditioners were not always ubiquitous. I know the brown, faux-wood-paneled Fedders unit in my parents’ bedroom didn’t have one; you could turn its dial only toward “high cool” or “low cool,” and adjust the speed of the fan. The key moment in the MONEY SAVER –ing of America’s ACs seems to have arrived in the fall of 2013, when manufacturers had to meet new criteria for their room air conditioners to receive an Energy Star certification. (You may see that program’s rectangular logo, a selling point that signals higher efficiency and lower bills, on some of your appliances.) Each new Energy Star–certified AC would have to include an extra-efficient operating mode, according to the updated rules, and that mode would have to be engaged automatically whenever the appliance was switched on. This latter point was important: An energy-saver mode wouldn’t just be present in all Energy-Star ACs—it would be the default .

The point here was to cut back on ACs’ energy consumption, but the rules themselves went only so far. They said that when an air-conditioner was operating in energy-saver mode, its fan would have to be shut off, for the most part, unless its compressor was also active. (In a unit’s normal cooling mode, the fan might be left on even when it isn’t doing anything to cool the room.) This may save a bit of money, but it’s pretty small potatoes, because the fan accounts for just a small proportion of an AC unit’s energy consumption. Beyond that, manufacturers had leeway to determine other details of how a money-saver mode might work. “We tried to build in a little bit of flexibility,” Amanda Stevens, who was then the EPA’s product manager for Energy Star home appliances, told me. (She’s now at Eversource, an energy provider in New England.) I asked Stevens why, if money-saver mode really did improve efficiency at little or no cost to thermal comfort, she and the EPA hadn’t pushed harder, so that it would be the only mode available on air-conditioners. “It’s a valid question,” she said.

AC manufacturers didn’t seem that eager to provide me with more detail. I reached out to a few of the bigger ones. After a couple of weeks’ delay, GE told me that in its units’ eco mode, the fan turns off when the compressor is offline, in keeping with the Energy Star specifications. In response to multiple requests for information, Electrolux, which owns the Frigidaire brand, finally sent me a similar explanation and a link to an Energy Star fact sheet. But the Frigidaire website gives a different explanation to appliance owners: An AC in energy-saver mode turns off when the set-point temperature is reached, it says, then tests the air every 10 minutes to determine whether it should turn on again. (Presumably an AC will also cycle on and off in normal mode, to maintain the set-point temperature.) Midea never responded to my inquiries.

“There’s not a standardized definition of this eco mode or energy-saver mode,” Jordan Clark, an HVAC-systems expert at Ohio State University, told me when I reached out to him in desperation. He confirmed my hunch that the details vary from manufacturer to manufacturer. Some models might merely switch off the fan as required and leave it at that. He suspects that others also slow down the rate at which they cool a room. That could make an air conditioner more efficient, he told me, while limiting the total amount of heat it can remove. Given 2024’s particularly frequent and intense heat waves, your window unit may end up struggling to reach the set point that you want, he said: “This is probably not the time when you would want to put it into that eco mode.”

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Elliott Gall, a building-sustainability expert at Portland State University, told me that he’s been curious about the high-efficiency setting on his own central-AC system. As far as he can tell, when the system is in normal mode, it calculates the average temperature inside his house, as measured across three sensors located in different rooms. Then the system turns on or off as needed, to keep the average at his chosen set point. In eco mode, however, he’s found that the system seems to focus on the sensor in his den, which tends to be several degrees cooler than his children’s bedroom upstairs. As soon as the den reaches the target temperature, the whole system shuts down. “It really seemed like it was just kind of playing games with multiple readings,” Gall told me.

These were just the one-off explanations, though. Almost everyone I spoke with for this story, including Clark and Gall, brought up a different—and slightly more insidious—idea. Some AC models, they told me, might go about money-saving by running on a wider, warmer range of temperatures. In this scenario, your AC unit would be engaged in a gentle sleight of hand. When a unit runs in normal cooling mode with a set point of 72 degrees, it might allow the air inside the room to fluctuate between, say, 71 and 73. The AC’s compressor would cycle on and off in order to maintain a temperature within that range; in engineering terms, this is known as a “dead-band control.” With money-saver mode engaged, the dead band might be stretched up a bit, perhaps to 74. “It’s a little bit sneaky,” Clark told me. “It ends up being a little bit hotter in your room for more of the time, but hopefully you don’t notice that because it’s only one degree and not all the time.”

Sneakiness aside, these controller shenanigans will provide some modest energy savings, Stefano Schiavon, a professor at the Berkeley College of Environmental Design, told me. And in his view, they would not have ill effects on people’s comfort. Schiavon told me that he’s not even sure anyone would notice temporary bumps in indoor air temperature from 73 to 74 degrees. (In a study done in Singapore, Schiavon showed that you can get away with raising the set-point temperature in an office by 5 degrees, and save a huge amount of energy, so long as workers also had control of nearby ceiling fans, which are far less energy-intensive than air conditioners.) Other experts, however, seemed to find the whole idea a bit distasteful. “There is no net gain from this. You save some energy by accepting less comfort,” Reinhard Radermacher, the director of the University of Maryland’s Center for Environmental Energy Engineering, told me. In this scenario, an AC in money-saver mode isn’t operating with more efficiency so much as providing less cooling . “The expectation is that maybe you don’t notice it, or it’s not bad enough that you do something about it,” Radermacher said.

The ACs that I have at home may not employ any of these tricks. It’s possible that their money-saver modes work only and exactly as required by the Energy Star specifications. (I can certainly hear their fans switch off between each cooling cycle.) But either way, the effects of running them this way are unmistakable: It’s hotter in the house. And the fact that money saver goes on by default is irksome of its own accord. I want to save money on my air-conditioning, but I can accomplish that by turning up the number on my thermostat. That’s not only more transparent; it’s more precise and economical, and better for the planet too. It’s more “eco,” if you will.

“Playing with the dead band may provide some savings, but not major, I would say,” Schiavon told me when I asked whether money saver might allow a drift in temperature around 72 degrees. Why not suck it up and leave your room a little warmer to begin with? Earlier, Schiavon had paused to give me some advice: “A side note, 72 is very low. You can keep your room at a much higher temperature than that.”