Well, I've had my 600w hps running for a month now with the glass in place without venting. I have my 8in wind tunnel pushing 700cfm's out of the grow room constantly and the room is less than 700 so that could be why I can hold my hand on the glass without getting burned. I have two 1yr old bulbs so im not too scared about blowing a bulb. Maybe someone can convince me to pull the glass out with their past experiences but so far no problems!