I rendered a short animation using Eevee engine, but my cpu was used 100% of the time. The temperature and fan of the cpu went crazy. How is that possible? Eevee is supposed to use OpenGL and has nothing to do with the settings in preferences, correct me if I'm wrong. I do have Cycles on GPU Compute and Cuda selected in Preferences with no CPU, but that shouldn't matter anyway. I have my both monitors plugged in the GPU display ports. It's a RTX 2070. I rendered the animation 3 times and checked the hardware with CAM and Task Manager. Why is Eevee using my CPU instead of GPU???
If anybody runs into the same problem in Eevee where the cpu is overloaded while rendering check your Compositing mode and make sure you don't have a Denoise filter on. It doesn't create a problem when you render in Cycles but it does put stress on the cpu when rendering with Eevee.
From the Blender Manual:
Being a rasterization engine, Eevee only uses the power of the GPU to render. There is no plan to support CPU (software) rendering as it would be very inefficient. CPU power is still needed to handle high scene complexity as the geometry must be prepared by the CPU before rendering each frame.
In short: CPU is still needed to prep the scene, GPU is used to render it.