Electric fans reduce core temperature and cardiovascular strain and improve thermal comfort in hot, humid conditions but are detrimental for all measures in very hot, dry conditions, according to a research letter published online Aug. 6 in the Annals of Internal Medicine.

Nathan B. Morris, Ph.D., from the Thermal Ergonomics Laboratory at the University of Sydney, and colleagues examined the effect of electric fan use on thermal strain, cardiovascular strain, risk for dehydration, and thermal comfort during a two-hour exposure to simulated peak conditions of a heat wave with hot and dry conditions versus cooler and more humid conditions with a higher heat index. Twelve male participants sat in a climatic chamber that simulated the conditions. Within each heat wave condition, the two-hour changes from baseline were compared between fan and control (without fan).

The researchers found that in very hot, dry conditions, fan use worsened rectal temperature, rate pressure product, heart rate, whole-body sweat rate, and whole-body thermal comfort. In hot, humid conditions, fan use improved each of these, except for whole-body sweat rate, which was worsened. There was no difference in systolic blood pressure with fan use in either heat wave condition.

"Fans could be encouraged as a cheaper and accessible alternative to air conditioning that also limits net electricity demand and carbon pollution," the authors write.

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