Insufficient partial heating based on the actual thermal demand of people or spaces becomes a revolutionary approach to reducing energy consumption. However, current research on local heating is case-specific and lacks standardized and unified guidelines for describing the formation of non-uniform indoor environments. In this paper, the local temperature imbalance rate and Part-Air Diffusion Performance Index (P-ADPI) parameters are proposed for multidimensional evaluation of indoor non-uniform environment characteristics. On the basis of the characteristic parameters, a unified indoor environment characterization partition was performed in the study. The results indicate that an increase in air supply temperature and air supply velocity could enlarge the characteristic core area and transition area. The intervention of background radiation conditions could intensify the inhomogeneity of the indoor environment, but it would have a minimal impact on the classification of the environment. The background radiation condition was incorporated into the characteristic boundary function model as a correction factor, and the correction factors for determining the background radiation temperature, position and the area fall within the ranges of 0.97–1.44, 0.82–1.01 and 0.98–1.10. This study has provided the groundwork for future studies on the local convection heating and the creation of a non-uniform indoor environment.