Abstract The ability to operate factory buildings as free running will be very useful in the context of saving energy needed for providing adequate thermal comfort for workers in warm humid tropical climatic conditions. The upper limits of thermally comfortable temperatures were established with comfort surveys carried out in three factory buildings without much ventilation. The surveys were then repeated to determine the effects of ventilation as well. The comfort surveys indicated that workers acclimatized to warm humid climatic condition could tolerate up to 30 °C without much ventilation when engaged in light factory work. This comfort temperature limit can be increased up to 34 °C when indoor air velocities are maintained as high as 0.6 m s −1 . It is also shown that these studies validate the earlier predictions of adaptive models for warm humid climates. The ability of workers to tolerate elevated temperatures could be used to highlight some concepts that can be considered in the planning of large-scale industrial parks, so that factories could be operated with minimum energy allocated for providing thermal comfort.