NOTE: The green areas show the temperature and relative humidity conditions in which the use of fans provides more cooling to the human body of a standard subject than still air. In the dark green region, while the use of fans is still beneficial, people are most likely suffering from heat strain. The red area demarcates the region in which fans should not be used.

These results were calculated using the Gagge et al. (1971) heat balance model with modifications as described in the paper. The model is applicable to healthy adults. We assumed that dry-bulb air temperature is equal to the mean radiant temperature. Our tool does not provide medical advice. The WHO suggests to use fans only when temperatures are below 40°C (104°F).