The article deals with correlation analysis of district heating (DH) processes using temperature domain (TD) method based on investigation of outside temperature, Tout, as regressor and DH supply water temperature, TS, as regresent scatter plots more in details. In this regard, the Tout&TS-scatter plots being investigated were overlapped with the Tout&TS temperature field which consists of 1x2-degree Tout&TS-cell structure. In such way structured temperature field allows to create different size temperature domains, TD, depending on specific properties of the scatter plots, e.g., depending on particularities of supposed regression line or (Tout'I; TS'i)-points density. Thus, the TD-method allows distributing the complete Tout&TS-scatter plot, containing in this case 4608 (Tout'I; TS'i)-points, in to several specific sub-TD. These sub-TD's, containing corresponding subsets less than 4608 (Tout'I; TS'i)-points of the complete heating season TD (HS-TD), have been investigated as separate statistical objects and corresponding regression models within TD have been developed.