A body heat source can be assigned in any load case.
In the name.iB file, a vector is first defined using a VV set:
VV set number T 6 V $\dot w$
and the set thus defined is then assigned to the selected elements:
AS load case number /$\dots$ /V set number E element number list /$\dots$
where $\dot w~[\text{W}/\text{m}^3]$ is the power of the heat source.
Note
The components of the vector can depend on the global coordinates $x,y,z$, using any of the available functional dependencies, see the Reference Manual.