2 FANS on 1 WYE DUCT, what happens?

If I were to put 2 x 8" cans fan onto a 8 x 8 x 12" wye forcing air out the 12" side, how much static pressure would i be dealing with?

Would this setup be inefficient? I need 1 fan to cool my lights and the other will be used to create negative pressure (outside of the grow room).

I wont be as efficient as running 2 separate exit's for the fans. I just did something similar in my room but I am switching to a sealed room and just air cooling the lights. You might want to think about a backdraft damper on the lighing duct to prevent air from back flowing when the lighting fan is off and your exhaust fan is still running.

Each 8" round is 50 sq inches, the 12" is 113 sq inches. You should have no pressure build up problems. Use rigid pipe with minimal turns from the "Y" out for best results.

What if from the 12" duct the exit hole is only 8"? How much wg inches would i possibly be looking at?