[RobsGreen]

Its probably best to leave the co2 especially if you don't want to waste money case that would probably do it. I've been wanting to do this as well but it has to be done properly to get the results you'll expect from it. The only way is to have the cab 100% sealed with no venting at all, have a fan cooling the light and then pump cold air into the box to keep the cab temp down. It would cost quite a bit to setup and an air conditioner would likely be needed and we know those are cheap to have plugged into the wall. The best advise I got was forget about it and concentrate on getting the environment perfect through the entire grow, that will likely give you better results then messing around with co2 when you need to vent. Good venting will keep the co2 level in the box the same as it is all around you which is plenty for plants. I also have my fan run all the time when the light is on, it would be fine to only have the fan trigger when the temp rises, I did that for a while but was worried my glass would break from the heat, its not tempered glass just regular.