Hi SimonSaysSmoke,
18 hours on 6 hours a day off will keep your babies in veg, the 6 hours off will give them a rest from the heat,
It has already been said because you are drawing the warm air form the grow space into your room which is simply making your grow space warmer, you need fresh air flowing into the grow space that should cool it down a bit, it will also give your babies oxygen, they dont survive to well without it dont you know.