I own 2 NBG6817 and several Netgear R7800. The Zyxel devices runs very hot with 80C° compared to Netgear that are all at 60C°. I used an infrared camera to check the sensor reading and they are right.
Is this normal? All devices runs without any problems but the difference in the temperature with the same chipset looks strange for me.
The nbg6817 is running hot, hotter than the r7800. ZyXEL hasn't made that great decisions when it came to its thermal design, the heat sink is relatively small and the airflow inside the case is rather bad - so around +10°C is to be expected. With ipq8065 as a SOC already being on the hotter side, 70-75°C is within the expected range for the nbg6817 (especially on hot summer days), >=80°C feels a tad much though.
Many modern wifi routers opt for a vertical design, improving the thermal design and its tendency to facilitate natural convection with a chimney effect that way, if they don't use active cooling to begin with. The flat and horizontal design of the nbg6817 really is the complete opposite to this, it might make sense checking how it behaves when hanged on a wall - opening the top case (over the heat sinks) a bit more might be a next step.
perhaps the netgear r7800 are taller or with more ventilation holes or have put some aluminum to dissipate the heat, if you own both notice the differences on the outside or inside
The difference is both visible with inbuild sensors and IR cam. I but the nbg6817 on the wall and the temperature is going down 3-4 points. Thats rights, so it is not a faulty device or something simply bad design of the hardware. More or less good to know.
Would such temperature lower lifetime so I should open the case a little?
Mine has done five years heavy duty in 24/7 operations, under a black tiled roof and during hot summers - it's still working fine, but I needed to switch to something with faster routing capabilities in early 2022 (relegating it to standby- and experimental uses).