Our summers are getting hotter, but electric fans are not always the answer—even if they make you feel cooler.
Electric fans work by blowing cooler air across our skin and enhancing the evaporation of our sweat. Cheap and convenient, they often sell out in heatwaves.
But on really hot days, a fan can flip from saviour to sauna—more convection oven than a breath of fresh air.
So where is that threshold? Public health bodies have advised that older people—who sweat less, and are more vulnerable to heat—shouldn’t rely on fans when it’s hotter than 35 degrees Celsius. Modelling by one group of scientists suggests the limit is 33 degrees, while another model spat out 38 degrees—a pretty significant divergence.
Fergus O’Connor, an Australian environmental physiologist at Queensland’s Griffith University, and his colleagues decided to test this question in the lab. They convinced 18 people aged between 65 and 85 to swelter in a 36-degree room for eight hours under three conditions—no fan, a fan on low, and a fan on high. The fan was placed a metre away, blowing directly on their skin (too ruffly to read a newspaper or magazine, but the volunteers were allowed Netflix and e-readers).
During all of the tests, the subjects’ body temperatures spiked to a mean of 38.3 degrees. “The fan had no benefit whatsoever,” says O’Connor—though it didn’t make things worse, either. Under the highest setting, blowing at four metres per second, subjects reported feeling slightly cooler, but their body heated up regardless.
O’Connor’s team haven’t yet tested the fans under other temperatures. But he advises that when the mercury rises past 33 degrees or so, you’re better to find an air-conditioned public space—perhaps your local library—rather than rely on a fan.