I've had several HPs over the years, including ZBooks, and every single one got very hot and blasts the fans all the feckin time :/
They were all company machines, but it's put me off ever buying one myself.
The 840 G3 was similar in this respect (that's how I discovered the Elitebook, the lab had an agreement with HP at the time), except I had to turn off the secondary HDD I chose to take when tweaking the configuration with hdparm -Y.
Though the ZBook seems more focused on performance than the Elitebook, so maybe the Elitebook will not cut it if you expect similar performance.
The ThinkPad actually spins its fans more easily than the HP I think, but it is also more powerful. The HP's noise when the fan do spin is also less annoying than the ThinkPad, it's a soft blow.