active intake no exhaust?

Ok so right now i have a 4x2x5 flower room I have a 600 watt hps about to be vented up into the cieling with an aircooled hood leaving one side opennow I wanna completley seel off my light from my room and start using a co2 bag called exhale now my question is I still may need an intake for the room itselfe to bring in cool air since uts going to be summer soon but I don't want to have an exhaust in the room because I don't want the co2 from the bag to be immediatly sucked from the room has anyone used an active intake with no exhaust will this work and would it help the room stay cool as well as keep the co2 in it? I know when using co2 temps should be 80-90 but I got a feeling with no having any intake for the cool air from my ac it might spike over 90 in there during summer