Fresh air needed?

I have a sealed room with a CO2 burner holding the co2 at 1200ppm do i have to have fresh air? I do have fans circulation the Co2 but i don't know if i need to pump fresh air in there or no.

anyone ? everytime i ask a question on Co2 i get no answers =/

You definitely need fresh air.

just make a small hole for air to come in, if you get any heat problems you might also need a vent fan to take out hot air.

what kind of lights are you running?

I am running 2 1000 hps vented out of the room. I don't under stand why i need fresh air if plants only use co2 and im giving them all the co2 they need and circulating it why fresh air can someone explain