Extremely hot and humid environments are common in numerous occupational settings. Construction work is tough and physically demanding, and the difficulty is exacerbated by the hot and humid weather of tropical and subtropical regions. Having established heat stress models through different environmental indicators, this study aims to ascertain which environmental indicator would be better able to predict the effects of heat stress on construction workers. Field studies were conducted during the summer in Hong Kong from July 2011 to August 2011. Physiological, work-related, environmental, and personal parameters were measured to validate the established heat stress models on the basis of 411 sets of synchronized meteorological and physiological data collected from construction workers on two different construction sites. The mean absolute percentage error (MAPE) and Theil's U inequality coefficient were used to assess these models in terms of predictive accuracy. The wet bulb globe temperature (WBGT) was found to have the highest validity (MAPE=6.5%; Theil's U inequality coefficient=0.05) and practicality in predicting the effects of heat stress on construction workers. Specific heat stress guidelines can be formulated based on the WBGT, which can protect the health and safety of site personnel working in hot and humid weather conditions.