In our research, CFD analysis of existing panel radiators were made with a commercial CFD code of STAR-CCM+ with variable connection methods. Numerical thermal performance values were obtained and were compared with given catalogue values. Panel-convector-convector-panel, Type-22-600x500 steel panel radiator was used in numerical study. For TBOE connection, mass flow rate distribution is greater than exact flow at first two and last three vertical ducts. In the middle of the vertical ducts towards inlet boundary values of mass flow rate corresponds to about zero. For TBSE connection, mass flow rate distribution is greater than exact flow at first four vertical ducts. In the last part of the vertical ducts mass flow rate distribution corresponds to about zero. Numerical results and commercial catalog values are very close each other for TBOE and TBSE connection, as a result two basic connection methods can be used for this panel radiator.