Factors that affect thermal sensations of comfort including the role of radiative energy exchanges between various surfaces in the room are discussed. It is shown that limitations in the uniformity of conditions influencing comfort may be imposed by the nature of the room and its occupancy, by the system capability and controllability, and by the air distribution in the room. Systems can be designed for increasingly refined performance at increased cost, subject always to the limitations inherent in the characteristics of the space and its occupancy.