TL;DR: I can’t stand high heat network devices 
It’s a standard PC case 14cm X 14cm fan.(low rotation speed but high flow capacity) to blow the heat from the buttom of the router.
Yes, my MV1000(W) is always on and hot, no matter what the loading is, that’s why I need to find a way to cool it down.
MV1000(W) should be tested in high heat environment before it’s out of factory, but cooler temperature will keep it work better and prolong the life of electronic components inside I guess.