I've just experienced same heat probs and I was running 270cfm exhaust with 80cfm at the intake for a 640cfm room. It was not enough, but I was running 3 600w lights. Solution was more construction to set up an in-line airflow through the lights. If this is not an option, I would upgrade my exhaust and place the 100cfm at the intake. If this is not enough just run the intake fan constantly, while the exhaust run intermittently as necessary. And as mentioned earlier, Co2 helps. Play it safe and make changes before plants are in.