That's ok, a lot of people end up putting everything in the subject line. The site does leave a lot to be desired.
Every model of the NUC has a cooling unit attached to the processor (and chipset). It consists of a heatsink and a blower (not a fan, per se). The blower that will push air over the heatsink, pulling heat from it, and then exhausts this air from the chassis. The inlet openings in the chassis are placed so that the air will travel across the surface of the opposite side of the board, including over the Memory DIMMs and the M.2 SSD (if present), before going to the opposite side of the board and into the blower. This airflow will extract heat from (and thus cooling) these other components. It was found that the M.2 SSDs could still run a bit hot and a piece of heat conducting foam was added to transfer heat from the SSD and dissipate it through the chassis. In the "H" models, there is also a drive bay for a 2.5" HDD/SSD/SSHD. This bay is designed so that the heat from the HDD/SSD/SSHD will be dissipated via the aforementioned airflow and also through the chassis. In my observation, this works fairly well, though temperatures in these drives may be higher.
Whether your particular unit has a drive that is actually suffering from overheating is something that you will have to determine. To check, run a tool that will display its temperature. Most HDD/SSD/SSHD drives can sustain fairly high temperatures without issue. If you are seeing temperatures that stay below 65°C while the system is busy, you have nothing to worry about. The best tool I have worked with for sensor display is FinalWire's AIDA64 (AIDA64 | The Ultimate System Information, Diagnostics and Benchmark Tool), though this is one that (outside of a trial period) will cost you money. Free alternatives (not as good but usually sufficient) include SpeedFan (SpeedFan - Access temperature sensor in your computer), HW Monitor (CPUID.org), HWINFO (HWINFO Diagnostic Software), etc.
Hope this helps,
I forgot to add. There is support in the BIOS for (1) increasing the minimum speed (minimum "duty cycle" (percentage of full speed) they call it) of the "fan" (blower), (2) lowering the minimum temperature (below which the fan is going to run at its minimum duty cycle) and (3) raising the rate at which the fan duty cycle is increased as the temperature rises (above the minimum). There are also modes that automate the handling of these settings (you could make the change from Quiet or Balanced mode to Cool mode to increase the cooling applied, for example).
To access these parameters, click on the Advanced box (top center of main Visual BIOS display) and then select the Cooling tab...
Help this helps,
Some models have a CPU with a TDP (Thermal Design Power) at 28 W
The NUC5PGYH have a TDP at 6 W. So I don't think you should worry too much about the heat.
And thanks to Scott for a trip through the airflow in a NUC - Thanks.