Is it recommended to install two fans for a sealed enclosure?

[curious aardvark]

I and family members have been feeling sick for abut three days after printing PETG in a toilet for about 7 hours. I guess even with the ventilation on, printing for so many hours created a large concentration of fume that were released when I opened the door. There are also scientific studies to show that even PLA emits invisible toxic nanoparticles that can enter the bloodstream.

Fair enough :-)

Although there has yet to be any conclusive toxicity studies - pretty sure I've read everything over the last 10 years or so.

But if you're going to concentrate any fumes in a small space without ventilation for 7 hours and then breath them all in at once - I can see where you might get issues :-)

So you basically want an in fan at the top of an enclosure facing the room and an out going through some dryer ducting and out the window.
You can print a nice adaptor for the window.

Try and avoid any direct airflow at the level of the build plate.

you could probably get away without an active exhaust as the hot air will create it's own draft - like a chmney does. But that can be an issue if it gets windy utside, so keeping up the negative pressure inside the enclosure doesn't hurt.