Co2 venting question

Im currently running a 10x5 room with 3 600w hps and supplying it with co2. Im wondering if I vent some cold air from outside into the room to help cool some. if it will lower ppm levels and the co2 will kick in more often. other than that its a closed system vent in vent out completely sealed. if so how much if you have any idea thanks

of course .. . .

you cant technically add air, with out something coming out some how. if not your room would pressurize and explode! LOL
so yeah if air comes in, some must come out some how. and it will lower your PPM.

yeah i wounder how much..cost it will run me