Guidelines for Thermal Boundary Conditions
When defining thermal boundary conditions, be aware of the following:
The software considers locations at which you have not created prescribed temperatures, convection conditions, radiation conditions or heat loads to be insulated.
The software determines the temperature at every location of your model for which you have not prescribed a temperature.
You do not have to select a boundary condition set to run a transient thermal analysis. However, if no set is selected, you must select at least one load set for the analysis to be valid.