system
A chat on subreddit /r/pcmasterrace
human
Is it safe? Technically, yes. Nothing extra will happen. 

BUT. You will be circulating a lot of hot air down there which is overall not good for the PC overtime. If the heater is on obviously. 

I’d move it or turn the heater off.
gpt
Not really, he will pull his air in at the front which will be ambient, exhaust out the back and physics will make the hot air rise and the cold air drop, especially as the desk isn’t above the heater, plenty of space for the hot air to escape. It’ll be fine