The cost to get enough CO2 to ventilate the room properly would far outweigh the heat issue and not have any real effect on the heat. The lights/power supplies generate the heat. The above ground plant can take temps well into the 100's, but not if the roots get above 80-85 degrees F. In the summer I put my pots directly on an uninsulated concrete floor to keep them cooler, that being about the best I am willing to work for.

So in summary, control the root temp and keep air moving for transpiration and you will be fine.