Co2 and Venting

i will be growing in a cabinet and thinking about doing the co2 thing with either a co2 tank or the yeast method.The thing that im stuck on is if im venting the air in the cabinet to the outside that means the co2 thats supplied by my co2 tank or yeast will be sucked out as well.So the question is how is it possible to use the co2 with out it being vented out?

If your cabinet is well sealed, you can set up a timer that shuts off the exhaust fan while you fill the room with CO2 then turn it on to change the air every hour or so.

You could do like I am going to do and use a cool tube reflector.... that way you can cool your light and not have to change the air as often.

unless your using HID theres no point in co2 supplemetation.

i'm using an active air co2 system. the easy way to sync is to buy matching timers with 15 min increments. you have to do a bit of math to figure out your flow rate. i have the exhaust/intake on 45 min of every hour and the co2 for the last 15 min. my closet is pretty small so my flow rate is small. we shall see how long a 25lb tank last.