I read a lot from people that when they start UE4 their hardware is getting hot and so the fans rev up even when starting with some basic samples.
But unfortunately even the most basic demo content in UE4 uses top notch visual technology and all post processing one could imagine which puts a high pressure on the hardware. Additionally there is no frame limiter activated in the Editor by default so most machines that are not water cooled are going crazy after some time or at least more noticeable.
While is all nice to show off… an interested developer could get the impression that UE4 is just too much next gen or just too inefficient to use for real projects on current hardware.