To assess the thermal component of human climate, the adequacy of two body-environment energy balance models is tested. Requirements are that these models should include the full range of atmospheric variables using a system which embraces both the attributes of those exposed and the functional attributes of the environment. They should also account for thermal stress on the body as well as the feedback thermophysiological responses as a result of that stress, and produce a unitary thermal index. Based on detailed field assessment, the study provides an interpretation of index values in terms of thermal sensation and pleasantness using standardised verbal scales. Detailed statistical analysis shows that the associations between index values and thermal sensation votes are strong giving correlation coefficients in the order of 0.86 which is considerably larger than those from comparable results reported in the literature. Optimal thermal conditions for sedentary activity appear to be located in the zone of vasomotor regulation against heat, subjectly interpreted as slightly warm, rather than precisely at the point of minimum heat stress. Sensitivity of model output and thermal sensation are greater in the zone of heat stress than in the zone of cold stress.