Boundary layer in thermal analysis

Hello expert,

I have a question about modelling for CFD analysis.

As my understanding, for flow simulation, we need to create boundary layer meshing based on velocity, material viscosity, length scale,..

But what if the simulation only have thermal conduction, no flow at all, no Fluid, do we need to mesh boundary layers?
If yes, how can we calculate the BL mesh size (first layer thickness)?

In OptiStruct, they don't create BL mesh for thermal analysis.

Thank you!